ISSN 2320 - 9569
International Journal of Emerging Trends in
Electrical and Electronics (IJETEE)
Volume 2, April Issue.
(Online Journal)
Published by
Institute of Research in Engineering & Technology (IRET)
Nagulapalli, Visakhapatnam, Andhrapradesh, India-531001
(www.iieee.co.in)
International Journal of Emerging Trends in Electrical and Electronics
ISSN-2320 – 9569
Editor in Chief
Dr. TAN CHER MING
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Prof. in Nanyang Technological University (NTU) and Director of SIMTech-NTU Reliability Lab.
Editorial Board Members:
Dr. Dhrubes Biswas,
Indian Institute of Technology, Kharagpur, India.
Dr. Kishore Kumar T
National Institute of Technology, Warangal,
India.
Dr. Rajesh Gupta
Indian Institute of Technology Bombay, India.
Dr. Gargi Khanna
National Institute of Technology Hamirpur, India.
Dr. Sumana Gupta
Indian Institute of Technology Kanpur, India.
Dr. K.S.Sandhu,
Ntional Institute of Technology Kurukshetra,
India.
Dr. A.K.Saxena
Indian Institute of Technology, Roorkee, India.
Dr. Vijay Kumar
Indian Institute of Technology Roorkee, India.
Dr. Om Prakash Sahu
National Institute of Technology, Kurukshetra,
India.
Dr. Shaibal Mukherjee
Indian Institute of Technology Indore , India.
Dr. K. P. Ghatak
National Institute of Technology, Agartala, India.
Dr. S.K. Parida
Indian Institute of Technology Patna, India.
Dr. Ajoy Kumar Chakraborty
National Institute of Technology, Agartala, India.
Dr. Manoj Kumar Meshram
Indian Institute of Technology(BHU) India.
Dr. SubhadeepBhattacharjee
Ntional Institute of Technolgy (NIT), Agartala,
India.
Dr. SatyabrataJit
Indian Institute of Technology (BHU), India.
Dr. Rama Komaragiri
National Institute of Technology Calicut, India.
Dr. Surya Shankar Dan
Indian Institute of Technology Hyderabad, India.
Dr. Elizabeth Elias
National Institute of Technology Calicut, India.
Dr. Rajib Kumar Jha
Indian Institute of Technology Ropar.
Dr. S. Arul Daniel
National Institute of Technology,Trichy, India.
Dr. Amit Mishra
Indian Institute of Technology Rajasthan, India.
Dr. BidyadharSubudhi
National Institute of Technology Rourkela, India.
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Nanyang Technological University, Singapoore.
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International Journal of Emerging Trends in Electrical and Electronics
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National Institute of Technology Rourkela, India.
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National Institute of Technology, Durgapur,
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Dr Ajay Somkuwar
Maulana Azad National Institute of Technology
Bhopal, India.
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Andhra University,
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National Institute of Technology, Durgapur,
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Velammal College of Eng. & Tech. Madurai.
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National Institute of Technology, Durgapur,
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SAEC College of Engineering, Chennai, India.
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National Institute of Technology, Silchar, India.
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Thiagarajar college of Engineering, Madurai,
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National Institute of Technology Silchar, India.
Prof. Anoop Arya
M.A.N.I.T(Deemed University),Bhopal, India.
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SV National Institute of Technology, Surat, India.
Mr. Navneet Kumar Singh
MNNIT Allahabad, India.
Dr. SwapnajitPattnaik
Visvesvaraya National Institute of Technology,
India.
of
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M.A.M College of Engineering, Tiruchirapalli,
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National Institute of Technology, Durgapur,
India.
Dr. Deepak Kumar
M.N. National Institute
Allahabad, India
ISSN-2320 – 9569
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NIT Agartala, India
Ms. LaxmiKumre
MANIT, Bhopal, India.
Technology
Miss. Joyashree Das
NIT Agartala, India.
Dr. ShwetaTripathi
MNNIT-Allahabad, India.
Dr. JishanMehedi
National Institute of Technology Silchar, India.
Mr. Santosh Kumar Gupta
Nehru National Institute
(MNNIT), Allahabad, India.
Dr. Balwinder Raj
National Institute of Technology Jalandhar, India.
M r. Mohamed. A. Elbesealy
Assuit University, Egypt.
Dr . S C Gupta
Maulana Azad National Institute of Technology,
Bhopal, India.
Mr. Hadeed Ahmed Sher
King Saud University, Riyadh, Kingdom of Saudi
Arabia.
Dr Ajay Somkuwar
Maulana Azad National Institute of Technology
Bhopal, India.
Mr. Syed Abdhul Rahman Kashif
University of Engineering and Technology,
Lahore.
ii
of
Technology
Mr. N. Peddaiah, Mr. K. Veera Sekhar, Mr. J. Lakshman and Mr. G. Rajashekhar
1
A Revolutionary Idea to Improve Power Quality
by Using Distributed Power Flow Controller
[DPFC]
Mr. N. Peddaiah, Mr. K. Veera Sekhar, Mr. J. Lakshman and Mr. G. Rajashekhar
Abstract: In the last few decades as the more increase in
population occurred so the usage of electric power is increasing
day by day and also the power companies are concentrating not
only on quantity of the power but also the quality of the power.
Here the new FACTS device is used called DPFC reduces the
voltage sag and voltage swell and improves the power quality.
According to growth of electricity demand and the increased
number of non-linear loads in power grids, providing a high
quality electrical power should be considered. In this paper,
voltage sag and swell of the power quality issues are studied and
distributed power flow controller (DPFC) is used to mitigate the
voltage deviation and improve power quality. The DPFC is a
new FACTS device, which its structure is similar to unified
power flow controller (UPFC). In spite of UPFC, in DPFC the
common dc-link between the shunt and series converters is
eliminated and three-phase series converter is divided to several
single-phase series distributed converters through the line.
Keywords: Distributed power flow controller, Power Quality,
Sag and Swell Mitigation.
I. INTRODUCTION
Most serious threats for sensitive equipment in electrical
grids are voltage sags (voltage dip) and swells (over voltage)
[1]. These disturbances occur due to some events, e.g., short
circuit in the grid, inrush currents involved with the starting of
large machines, or switching operations in the grid In this
paper, a distributed power flow controller, introduced in [9]
as a new FACTS device, is used to mitigate voltage and
current waveform deviation and improve power quality in a
matter of seconds. The DPFC Structure is derived from the
UPFC structure that is included one shunt converter and
several small independent series converters, as shown in
Fig.1.1The shunt converter is similar to the STATCOM while
the series converter employs the D-FACTS concept[9]. The
DPFC has same capability as UPFC to balance the line
parameters, i.e., line impedance, transmission angle, and bus
voltage magnitude [10].
The paper is organized as follows: in section II, the DPFC
principle is discussed. The DPFC control is described in
section III. Section IV is Simulation models. Results in
section V.and section VI is conclusion
In the last decade, the electrical power quality issue has
been the main concern of the power companies [1]. Power
quality is defined as the index which both the delivery and
consumption of electric power affect on the performance of
electrical apparatus [2]. From a customer point of view, a
power quality problem can be defined as any problem is
manifested on voltage, current, or frequency deviation that
results in power failure [3]. The power electronics
progressive, especially in flexible alternating-current
transmission system (FACTS) and custom power devices,
affects power quality improvement [4],[5]. Generally, custom
power devices, e.g., dynamic voltage restorer (DVR), are
used in medium-to-low voltage levels to improve customer
power quality [6].
Fig.1.1 DPFC structure
II.
Mr. N. Peddaiah is working as Asst. Professor, Dept of Electrical &
Electronics, KCE, Kurnool, India, Mr. K. Veera Sekhar is PG-Student, Dept
of Electrical and Electronics, SKDEC, Gooty, India, Mr. J. Lakshman is
working as Asst. Professor, Dept of Electrical & Electronics, SSCET,
Kurnool, India. And Mr. G. Rajashekhar is a UG-Student, Dept. of Electrical
and Electronics, KCE, Kurnool, India, Emails: peddaiah.n@gmail.com,
veeru667@gmail.com, lakshman36@gmail.com, rshekhar130@gmail.com.
DPFC PRINCIPLE
In comparison with UPFC, the main advantage offered by
DPFC is eliminating the huge DC-link and instate using
3rd-harmonic current to active power exchange [9]
Theoretically the third, sixth, and ninth harmonic frequency
are all zero sequence and all can be used to exchange active
power in the DPFC, as it is well known the capacity of a
transmission line to deliver power depends on its impedance,
since the transmission line impedance is inductive and
proportional to the frequency, high transmission frequencies
will cause high impedance. Consequently the zero sequence
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr. N. Peddaiah, Mr. K. Veera Sekhar, Mr. J. Lakshman and Mr. G. Rajashekhar
harmonic with the lowest frequency –third harmonic is
selected [9], In the following subsections, the DPFC basic
concepts are explained.
A. Eliminate DC Link and Power Exchange
Within the DPFC, the transmission line is used as a
connection between the DC terminal of shunt converter and
the AC terminal of series converters, instead of direct
connection using DC-link for power exchange between
converters. The method of power exchange in DPFC is based
on power theory of non-sinusoidal components [9]. Based on
Fourier series, a non-sinusoidal voltage or current can be
presented as the sum of sinusoidal components at different
frequencies. The product of voltage and current components
provides the active power. Since the integral of some terms
with different frequencies are zero, so the active power
equation is as follow:
2
The third harmonic current is trapped in trapped in ∆ -winding
of transformer. Hence, no need to use the high-pass filter at
the receiving-end of the system. In other words, by using the
third-harmonic, the high-pass filter can be replaced with a
cable connected between ∆-winding of transformer and
ground. This cable routes the harmonic current to ground.
∞
P= ∑V i I i cos φi
i =1
……………….
(1)
Where Vi and Ii are the voltage and current at the ith harmonic,
respectively, and φi is the angle between the voltage and
current at the same frequency. Equation (1) expresses the
active power at different frequency components is
independent.
The above equation (1) describes that the active power at
different frequencies is isolated from each other and the
voltage and current in one frequency has no influence on the
active power at other frequencies. so by this concept the shunt
converter in DPFC can absorb active power from the grid at
the fundamental frequency and inject the current back into the
grid at a harmonic frequency[9]. Based on this fact, a shunt
converter in DPFC can absorb the active power in one
frequency and generates output power in another frequency,
and also according to the amount of active power required at
the fundamental frequency, the DPFC series converter
generate the voltage at the harmonic frequency there by
absorbing the active power from harmonic components.
Assume a DPFC is placed in a transmission line of a two-bus
system, as shown in Fig.1. While the power supply generates
the active power, the shunt converter has the capability to
absorb power in fundamental frequency of current. In the
three phase system, the third harmonic in each phase is
identical which is referred to as “zero sequence”. The zero
sequence harmonic can be naturally blocked by Y-∆
transformer.
So the third harmonic component is trapped in Y-∆
transformer [9]. Output terminal of the shunt converter injects
the third harmonic current into the neutral of ∆ -Y
transformer. Consequently, the harmonic current flows
through the transmission line. This harmonic current controls
the DC voltage of series capacitors. Fig. 2 illustrates how the
active power is exchanged between the shunt and series
converters in the DPFC. The third-harmonic is selected to
exchange the active power in the DPFC and a high-pass filter
is required to make a closed loop for the harmonic current.
Fig: 2.1: Active power exchange
B. The DPFC Advantages
The DPFC in comparison with UPFC has some
advantages, as follows:
1. High Control Capability
The DPFC similar to UPFC, can control all parameters of
transmission network, such as line impedance, transmission
angle, and bus voltage magnitude.
2. High Reliability
The series converters redundancy increases the DPFC
reliability during converters operation [10]. It means, if one of
series converters fails, the others can continue to work.
3. Low Cost
The single-phase series converters rating are lower than
one three-phase converter.
Furthermore, the series converters do not need any high
voltage isolation in transmission line connecting; single-turn
transformers can be used to hang the series converters.
Reference [9] reported a case study to explore the feasibility
of the DPFC, where a UPFS is replaced with a DPFC in the
Korea electric power corporation[KEPCO].To achieve the
same UPFC control capability, the DPFC construction
requires less material [9].
III.DPFC CONTROL
The DPFC has three control strategies:
A.
Central Control
This controller manages all the series and shunt controllers
and sends reference signals to both of the shunt and series
converters of the DPFC.According to the system
requirements, the central control gives corresponding voltage
reference signals for the series converters and reactive current
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr. N. Peddaiah, Mr. K. Veera Sekhar, Mr. J. Lakshman and Mr. G. Rajashekhar
signal for the shunt converter. All the reference signals are
generated by central control are at the fundamental
frequency.[9]
3
transformer.
Fig: 3.1 Central Control
Fig: 3.3 Shunt Control
B. Series Control
Each single-phase converter has its own series control
through the line. The controller is used to maintain dc voltage
of a capacitor by using third harmonic frequency and to
generate series voltage at a fundamental frequency which is
prescribed by central control. Because of single phase series
converter voltage ripple will occur whose frequency depends
on frequency of current that flows through converter. So
eliminate this ripples there are two possible ways one is
increasing of turns ratio of single phase transformer and the
second is use of dc capacitor of large capacitance. Any series
controller has a low-pass and a 3rd-pass filter to create
fundamental and third harmonic current, respectively. Two
single-phase phase lock loop (PLL) are used to take
frequency and phase information from network [11].The
PWM-Generator block manages switching processes.
IV. SIMULATION MODEL FOR DPFC
Fig: 4.1.Simulated model for DPFC
Within the setup, multiple series converters are controlled by
a central controller. The central controller gives the reference
voltage signals for all series converters. The voltages and
current within the setup are measured by its simulink outputs.
Fig: 3.2 Series control
C.
Shunt Control
The shunt converter includes a three-phase converter
connected back-to-back to a single-phase converter. The
three-phase converter absorbs active power from grid at
fundamental frequency and controls the dc voltage of
capacitor between this converter and single-phase one. Other
task of the shunt converter is to inject constant third-harmonic
current into lines through the neutral cable of ∆-Y
Fig: 4.2.Series Converter SIMULINK Model
The basic function of the shunt converter is to supply or
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr. N. Peddaiah, Mr. K. Veera Sekhar, Mr. J. Lakshman and Mr. G. Rajashekhar
4
absorb the active power demanded by the series converter.
The shunt converter controls the voltage of the DC capacitor
by absorbing or generating active power from the bus,
therefore it acts as a synchronous source in parallel with the
system. To verify the DPFC principle, two situations are
demonstrated: the DPFC behavior in steady state and the step
response. In steady state, the series converter is controlled to
insert a voltage vector with both d- and q-component, which
is Vse,d,ref = 0.3 V and Vse,q,ref = −0.1 V. The voltage
injected by the series converter, the current through the line,
and the voltage and current at the side of the transformer.
Fig: 5.3: Step response of the DPFC: active and reactive
power injected by the Series converter:
Fig: 5.4: Step response of the DPFC: bus voltage and current
Fig: 4.3.Shunt Converter SIMULINK Model
V. RESULTS
FIG: 5.5: STEP RESPONSE OF THE DPFC:SERIES CONVERTER VOLTAGE.
VI. CONCLUSION
Fig: 5.1: Reference voltage for the series converters
Fig: 5.2: Step response of the DPFC: line current:
To improve power quality in the power transmission
system, there are some effective methods. In this paper, the
voltage sag and swell mitigation, using a new FACTS device
called distributed power flow controller (DPFC) is presented.
The DPFC structure is similar to unified power flow
controller (UPFC) and has a same control capability to
balance the line parameters, i.e., line impedance, transmission
angle, and bus voltage magnitude. However, the DPFC offers
some advantages, in comparison with UPFC, such as high
control capability, high reliability, and low cost. The DPFC is
modeled and three control loops, i.e., central controller, series
control, and shunt control are design. The system under study
is a single machine infinite-bus system, with and without
DPFC. It is shown that the DPFC gives an acceptable
performance in power quality mitigation and power flow
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr. N. Peddaiah, Mr. K. Veera Sekhar, Mr. J. Lakshman and Mr. G. Rajashekhar
control.
APPENDIX
5
[11] R.Zhang,M.Cardinal,P.Szczesny and M.Dame “A grid
simulator with control of single phase power converters in D Q
rotating frame” power electronics spectalists conferecne IEEE
2002.
N. Peddaiah was born in Kurnool , India. He received the B.Tech
(Electrical and Electronic Engineering) degree from
Jawaharlal Nehru Technological University,
Hyderabad in 2006 and received M.Tech (Power
and
Industrial
Drives)
from
JNTUCE
(Autonomous), Anantapur in 2009. Currently he is
working as a Asst. Professor in Dept. of EEE in
KCE Kurnool. He has published several
International Conferences. His area of interesting power Electronics,
Electrical
Drives
and
FACTS
devices.
E-mail:
peddaiah.n@gmail.com
K. Veerasekhar was born in Seethampalli(V),
Kadapa, India. He received the B.Tech (Electrical
and Electronic Engineering) degree from R.G.M.
College of Engineering and Technology, Nandyal,
and pursing M.Tech (Electrical power Engineering)
from SKDEC, Gooty, Anantapur, His area of
interesting Power systems , HVDC,FACTS devices
and Power Quality, E-mail: veeru667@gmail.com
REFERENCES
[1] S Masoud Barakati, Arash khoskbar sadigh and Ehasn
Mokhtarpour,”voltage sag and swell compensation with DVR
based on Asymmetrical cascade multicell converter”,North
America power symposium[NAPS] pp1-7,2011.
[2] Alexander Eigels Emanuel,John A. Mcneill”Electric power
quality”annu.Rev.Energy Environ 1997,pp.264-303.
[3] I Nita R.Patne,krishna L.thakre “Factor Affecting Characteristics
of voltage sag due to fault in the power system”serbian journal
of Electrical Engineering vol.5no.1 may 2008,pp.171-182
[4] J R Enslin,”Unified approach to power quality mitigation”in
Proc. IEEE int. symp.Industrial Electronics(ISIE’98),vol 1,1998
pp 8-20
[5] B Singh,K Al-Haddad and A.Chandra “A review of active filters
for power quality improvement”, IEEE Transactions. And
.electron, vol 46 no.5 pp.960-971,1991
[6] M.A. Hannan and Azad Mohamed member IEEE
“PSCAD/EMTDC simulation of unified series-shunt
compensator for power quality improvement”, IEEE
Transactions on power Delivery vol.20 no.2 APRIL 2005.
[7] Ahmad Jamshidi , S. Masoud Barakati and Mohammad Moradi
Ghahderijani”Power quality improvement and mitigation case
study by using Distributed Power Flow Controller”IEEE paper
in 2012.
[8] R.lokeswar reddy(M.TECH) And K.vasu (M.TECH) “Designing
of Distributed power flow controller ” IOSR Journal of
Electrical and Electronics Engineering (IOSR-JEEE) ISSN:
2278-1676 Volume 2, Issue 5 (Sep-Oct. 2012), PP 01-09.
[9] zhihui yuan,sjoerd W.H de haan and Braham Frreira and Dalibor
cevoric “A FACTS DEVICE: Distributed power flow controller
(DPFC) ” IEEE transaction on power electronicsvol.25,no.10
october 2010.
[10] zhihui yuan,sjoerd W.H de haan and Braham Frreira “DPFC
control during the shunt converter failure” IEEE transaction on
power electronics 2009
J.LAKSHMAN was born in Kurnool , India. He
received the B.Tech (Electrical and Electronic
Engineering) degree from Sri krishna devaraya
university, Anantapur in 2006 and received M.Tech
(Power Electronics) from JNTUA, Anantapur in
2009. Currently he is working as a Asst. Professor in
Dept. of EEE in SSCET, Kurnool. He has published
several International Conferences. His area of interesting power
Electronics, Electrical Drives and FACTS devices. E-mail:
lakshman36@gmail.com
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
G.RAJA SHEKHAR was born in kurnool,
India. He received the B.Tech [ELECTRICAL
AND ELECTRONICS ENGINEERING] degree
from kottam college of engineering Kurnool,
Jawaharlal Nehru Technological University,
Anantapur
in
2013.
Email:
rshekhar130@gmial.com
Vol. 2, Issue. 1, April-2013.
6
Jayeshkumar G. Priolkar and Vinayak N. Shet
A Review on Protection Issues in Microgrid
Jayeshkumar G. Priolkar and Vinayak N. Shet
Abstract— Microgrid is cluster of distributed generation
sources, storage systems and controllable loads. Microgrid can
provide quality and reliable supply of energy to consumer.
Microgrid can operate in both modes of operations that is grid
connected mode and islanded mode. This implementation poses
technical challenge of protecting the microgrid. Power quality,
energy management, stability, power flow control, protection
system and integration of various distributed generators are the
major issues in the microgrid operation. This paper reviews
various protection issues in microgrid, various protection
schemes to overcome the protection issues are also discussed.
Implementation of adaptive protection system using digital
relaying and advanced communication is most successful
method of the protection of microgrid.
Index Terms— Distributed generators, Inverter, Microgrid,
Power flow control, Power quality Stability, Protection.
I. INTRODUCTION
Microgrid is one of the solutions to present energy crisis.
It is basically network comprising of distributed generation
sources, storage system and controllable loads, which can
operate in grid connected mode or incase of fault in isolated
mode. Microgrid provides various advantages to end
consumer’s utilities and society. Various advantages include
improvement in energy efficiency, minimisation of overall
energy consumption and improvement in service quality and
reliability of power supply [1]. The coexistence of multiple
energy sources which have versatile dynamic properties and
electrical characteristics have impact on safety, efficiency,
control and stability of microgrid.
Technical issues associated with operation of microgrid
are interconnection and the islanding mode. Interconnection
of microgrid with maingrid is complex; complexity in
interconnection is affected by the types of power generation
number of generating sources, location of points of
interconnection and level of penetration of microgrid system
with maingrid [2].
Jayeshkumar G. Priolkar is working as Assistant Professor and Vinyak
N. Shet is working as Professor in department of electrical & electronics
engineering at Goa college of engineering, Farmagudi, Ponda Goa, 403404.
( emails are 1. jayeshpriolkar@gmail.com 2. vns@gec.ac.in)
The increased penetration of distributed generation in
microgrid system poses several technical problems in the
operation of the grid such as steady state and transient over
& under voltages at point of connection, protection
malfunctions, increase in short circuit levels and power
quality problems [3].The major challenge in microgrid is the
protection system. Protection system must respond to both
maingrid and microgrid faults. Protection system should
isolate the microgrid from the maingrid as fast as possible to
protect the microgrid. When Distributed generators (DG) are
integrated to form the microgrid it is essential to assure that
the loads, lines and DG on island are protected. The fast
operation of protection improves the ability to maintain
synchronism after transition to islanded operation, which is
crucial from viewpoint of stability [4].
The various protection issues arises when the integration
of DG is done with distribution level network, there is
change in faults current level of network, possibility of
sympathetic tripping, reduction in reach of distance relays,
loss of relay coordination and unintentional islanding [5].
Protection problem arises in island operation with inverter
based sources as inverter based sources are limited by ratings
of silicon devices [6]. When microgrid is used to improve
service continuity, distributed network protections are need
to be modified. Automatic and fast operative devices are
used to detect faulty portion of network, which disconnects it
rapidly and automatically it will also reconfigure the network
depending upon requirement [7].
To overcome problems arising due to bidirectional power
flows, low fault current levels in microgrid with inverter
based sources a new portion system is required with
advanced communication system, with real measurements
where settings parameters and relay are checked and updated
periodically giving safe and reliable operation[2].
II. LITERATURE REVIEW
The various technical issues associated with the
integration of the grid, protection challenges and possible
solutions are discussed in [1]. Novel adaptive microgrid
protection scheme with advanced communication system is
also proposed in [1]. For proper integration of microgrid
conventional power system protection cannot be used. In
Paper [2] authors have reviewed the traditional power system
protection concepts and strategies, protection challenges
arising from integration of DG into the grid, alternate
protection strategies, their merits and demerits are also
discussed. The analysis of physical and electrical
characteristics of the microgrid, numerical simulations and
their influence on design of suitable protection schemes are
discussed in [5]. The application of local induction
generators on protection selectivity of the system with
parallel distribution feeders and defect on fault detection is
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
7
Jayeshkumar G. Priolkar and Vinayak N. Shet
discussed in [6].Design and implementation of control
scheme for microgrid is discussed in [7].Major protection
issues arises in islanded operation with inverter based
sources, this is mentioned in paper [8].For effective
protection, the parameters of the protective devices are to be
updated, and how the effective coordination is achieved is
discussed in detail in [9].Various technical issues of the
protection system with emphasis on protection coordination
problem is discussed in [10] .Innovative protection schemes
for multiphase and phase to ground faults in MV microgrid
are mentioned in [11]. In paper [12] coordinated method to
manage both network protection and DG interface protection
is proposed. Authors have proposed a protection scheme
using digital relays with communicated network for the
microgrid [14]. In order to provide an effective network
protection to meshed microgrid multilevel approach is
adopted in paper [15].The application of admittance relay for
protection of the converters used for distributed generator
sources is discussed in [16].Paper [17] proposes use of
microprocessor based relays for low voltage protection of
microgrid. Communication network to monitor the microgrid
and update the relay fault currents according to dynamic
changes in system such as connection/disconnection of
distributed generation sources is mentioned in [18].In [19]
various issues related to protection of microgrid are
discussed ,authors have used protection strategy, which
adaptively selects different fault detection methods in grid
connected mode and islanded mode, which improves the
selectivity and reliability in protecting the microgrid. Design
of microgrid protection system which makes use of current
limiters in fault current estimation and uses communication
network to monitor and update the relay fault currents
according to variations in the system
is proposed in
[20].Paper [21] discusses about the protection issues related
to inverter interfaced distributed generators and various
protection schemes available. In [22] for a particular
microgrid, protection scheme is developed which makes use
of abc-dq transformation of system voltage to detect
presence of short circuit fault and by comparing
measurements at different locations provides discrimination
between faults in different zones of protection. For
protection of synchronous based distributed generators,
scheme based on directional overcurrent relay is proposed in
[23]. Various protection techniques and control strategies
have been proposed to ensure a stable operation and to
protect the distributed generation sources [24 - 26].
III. PROTECTION ISSUES
Fault currents for grid connected and islanded operation of
microgrid are different. The short circuit power varies
significantly. Faults also causes loss of sensitivity,
overcurrent, earth leakage, disconnection of generators,
islanding, reducing reach of overcurrent relays , single phase
connections and loss of stability[2].Depending upon
location of faults with respect to distributed generators and
existing protection equipment, problems like bidirectional
power flow and change in voltage profile occurs. The power
output of distributed generators like synchronous generators,
induction generators and inverter interfaced protection units
is unpredictable due to which whenever there is a fault,
power output of these DG sources changes [5].Modification
in fault current level, device discrimination, reduction in
reach of impedance relays, reverse power flow, sympathetic
tripping, islanding, single phase connection, selectivity are
the key protection issues.
A. Modification in fault current level
When large number of small distributed generation units that
uses synchronous or induction generator units are connected
to distribution network or grid it changes fault current level
as both types of generators contribute towards fault currents.
When inverter interfaced DG units are used, fault current is
limited to a lower value [7,20]. As fault current is not high as
compared to load current, some of the relays do not trip,
others that respond to fault operate with the time delay. The
undetected fault spreads out in the system and can damage
the equipment [2]. Fault impedence also decreases when DG
is connected into network in parallel with the other devices.
When faults occurs downstream of the point of common
coupling, both the main source and DG contributes fault
current. Relay placed at upstream of DG measure fault
current supplied by upstream source. In Fig. 1 the relay
placed at the upstream of DG measure the fault current
supplied by upstream source. Actual fault current is
different, relays will not function properly and there will be
coordination problems. If there is short circuit fault, when
DG is integrated with the main grid it will affect the
amplitude, direction and duration of fault currents.
Fig. 1.Fault current contribution from DG and grid
B. Device discrimination
In the power system network that has generation sources
at the end of network , fault current decreases with increase
in distance as the impedance increases. The variation in
magnitude of fault current is used for discrimination. Incase
of islanded microgrid with inverter interfaced distributed
generation units , fault is limited to a lower value ,fault level
at the locations of feeder will be almost constant [9].The
traditional current protection scheme which uses the
variation in magnitude of fault current for discrimination
does not work properly. New protection system for device
protection is required.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
8
Jayeshkumar G. Priolkar and Vinayak N. Shet
C. Reduction in reach of Impedance relays
The reach of impedance relay depends upon the distance
between the relay location and fault point , maximum
distance means minimum fault current that is detected [2].
When DG is present in the system, distance relay may not
operate according to defined zone settings. When faults
occurs downstream of the bus DG connected to utility
network, impedence measured by relay located in upstream
is higher than real fault impedence. This affects grading of
relays and causes delayed operation or sometimes relay does
not operate at all.
D. Reverse Power flow
Main challenge for protecting the microgrid arises because
power can flow in both the directions in each feeder of
microgrid. Sources are located in both sides of load due to
which power flows in opposite direction from two sources
towards the load. Power flow also changes its direction
incase of distribution network with embedded generation
when local generation exceeds local consumption [2]. The
reverse power flow can also cause power quality problems
resulting in variation of voltage.
E. Sympathetic Tripping
This occurs when protective device operates for faults in
an outside protective zone. DG contributes towards the fault;
relay operates alongwith another relay which actually sees
the fault resulting in malfunctioning of protective scheme.
Relay on line 2 will unnecessarily operate for fault F1 at line
L1 as a result of infeed from DG to fault current as shown in
Fig.2
G. Single phase connection
Some DG sources inject single phase power into the
distribution grid, for example PV systems. This affects
balance of three phase currents, due to unbalance current in
the neutral conductor increases which also results in flow of
stray currents to earth. This current should be limited to
prevent overloading.
H. Selectivity
Protection system is said to be selective if the protection
device closest to the fault operates to remove the faulty
section. Without DG, there is power flow in only one
direction, during normal operation as well as when there is
fault, by using time graded overcurrent relays selectivity can
be obtained .When DG is integrated with the grid ,this
systems becomes inadequate. There is possibility of
disconnection of healthy feeder by its own protective relay
because it contributes to the short circuit current flowing
through fault in the neighboring feeder. The tripping current
for electrical protective device is between maximum load
current and minimum fault current. Fault current and load
current depends upon the state of grid, state of distributed
generators and whether microgrid is operating in islanded
mode [9].
.
The main challenge for protecting the microgrid arises
from the fact that power can flow in both the directions in
each feeder of the microgrid. Close to each local load, there
may exist two or more sources that contribute to the loaded
power. The sources are located in both sides of load due to
which power flows in opposite direction from two sources
towards the load
IV. CASE STUDY ON STUDIED MICROGRID
Particular case for the microgrid is considered for study as
shown in the Fig. 4. Different fault scenarios in microgrid
are considered to see the operation of circuit breaker and
coordination between circuit breakers as listed in Table I
TABLE I
Fig. 3. Underreaching of relay and sympathetic tripping due to DG
connection
F. Islanding
The DG creates a problem when part of distributed
network with DG unit is islanded. Islanding is due to fault
in the network. If generator continues to supply power
despite the disconnection of utility, fault might persist as
fault is fed by DG [2, 4]. If the control for the voltage is not
provided, it results in unexpected rise in voltage levels incase
of islanded operation.
MAJOR CLASSES OF MICROGRID PROTECTION [1]
Operating
mode
External Faults (Main grid)
Internal Faults (Microgrid)
MV
feeder,(F1)
LV
(F3)
Grid
connected
(CB1)
closed
Fault
is
managed
by
MV
system
Microgrid
isolation
by
CB1
incase no
MV
protection
tripping.
Possible
fault
sensitivity
problems
for CB1
Isolated
(CB1
open)
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Distribution
Transformer
(F2)
Fault
is
managed
by
MV
system
(CB0) .CB1 is
open by follow
me function of
CB0. Incase of
communication
failure
,sensitivity
problem
for
CB1
feeder
Disconnect
smallest
portion
of
microgrid (CB
1.2 and CB
2.1).CB 1.2 is
opened
by
fault current
from the grid
(high level).
Low level of
reversed fault
current causes
sensitivity
problems.
Disconnect
smallest
portion
of
microgrid (CB
LV
Consumer
(F4)
Faulty
load
is
isolated
by CB 2.4
or
fuse.
Incase of
no
tripping
the SWB
is isolated
by CB 2.5
&
local
DG is cut
off.
Faulty
load
is
isolated
by CB 2.4
Vol. 2, Issue. 1, April-2013.
9
Jayeshkumar G. Priolkar and Vinayak N. Shet
1.2 and CB
2.1).
Low
level of fault
currents
causes
sensitivity
problems for
both CB
or
fuse.
Incase of
no
tripping
the SWB
is isolated
by CB 2.5
and local
DG is cut
off
A. Fault Analysis
Scope of fault analysis in this paper is to estimate the
magnitude of current under short circuit condition. Fault
level indicates strength of system; selection of circuit breaker
and design of coordination system for protective relaying is
done based on fault analysis. Fault analysis in this paper
done for the typical microgrid as shown in Fig.4. The ratings
and parameters of the equipments considered for typical
microgrid for analysis is given in appendix. For fault
analysis base kVA selected is 630 kVA, base voltage is
400V and fault location is at F3. Table II indicates
comparison of fault currents for different faults, Table III
shows the comparison of fault currents in different modes.
From the fault analysis done it can be concluded that there
is change in fault current level during different modes of
operation in microgrid, which makes protection system
design for entire network complex.
V. POSSIBLE SOLUTIONS FOR PROTECTION ISSUES
There are various solutions available to overcome protection
challenges in the microgrid network. Whenever there is
reverse power flow or bidirectional power flow, main relays
of feeders which are fed from the substation can be
interlocked [11]. The use of directional over current relays
can also solve this problem. The other solution is main
feeder relay adjustment in terms of time settings. Feeder
without DG can have faster relay settings as compared to
feeder with DG.
A. Protection of inverter interfaced DG units
Conventional protection systems cannot give reliable
protection for inverter interfaced units, because there is
limited fault current. The solution can be achieved by using
inverters which have high fault current capability that is
uprating the inverter, using faster communication system
between Inverter and protective relays, and introduction of
energy storage devices that are capable of supplying large
current incase of faults [2].
B. Differential protection scheme
The conventional differential protection cannot give the
reliable protection. The protection scheme for microgrid
with Inverter interfaced DG units cannot differentiate
between fault current and an overload current, which results
in nuisance tripping when system is overloaded, in some
instances traditional protection scheme. For proper clearing
of fault in an islanded microgrid and to ensure selectivity ,it
is important that different distributed generators should
effectively communicate with each other. Use of evolving
distribution system version of pilot wire line differential
scheme is required for protection [2].
Fig. 4. Different Fault scenarios of Microgrid [1]
TABLE II
COMPARISON OF FAULT CURRENT FOR DIFFERENT FAULTS
Type of Fault
Location
Fault current
Three Phase
F3
14.57 kA
Single Line to Ground
F3
8.02 kA
Double line to Ground
F3
8.0 kA
TABLE III
COMPARISON OF FAULT CURRENT IN DIFFERENT MODES
Type of operating mode
Fault Location
Magnitude of fault
current
Grid
Connected
with
F3
14.57 kA
Islanded mode
F3
5.857 kA
Grid Connected Mode
F3
7.913 kA
DG
C. Balanced combination of different types of DG units
To obtain the protection of an isolated microgrid is to use
DG units with synchronous generators or to use inverters
having high fault current capability or to use combination of
both types of DG units so the conventional protection
schemes can be properly used.
D. Inverter Controller design
Protection scheme for islanded microgrid is dependent on
type of inverter controller, controller can actively limit the
available fault current from inverter interfaced distributed
generator units.
E. Protection based on symmetrical components and
differential components of currents.
Microgrid can be protected against unsymmetrical faults
based on symmetrical components. As per the studies carried
out for differential and symmetrical component of currents ,
a symmetric protecting the microgrid against all single line
to ground and line to line fault is developed[8,23].
without DG
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
10
Jayeshkumar G. Priolkar and Vinayak N. Shet
F. Adaptive protection for microgrid
Adaptive protection scheme solves the problem both in
grid connected as well as islanded mode [1,19]. In adaptive
protection system there is automatic readjustment of relay
settings when microgrid changes from grid connected mode
to islanded mode and from islanded mode to grid connected
mode. Adaptive protection is an online system that modifies
preferred protective response to change in system conditions
or requirements in timely manner by means of external
generated signals or control actions. Technical requirements
and suggestions for practical implementation of an adaptive
protection system make use of numerical directional
overcurrent relays. Numerical directional overcurrent relays
should have possibility of using tripping characteristics
(several settings groups) that can be parameterized locally or
locally. For effective protection make use of communication
system and standard communication protocol such that
individual relays can communicate and exchange
information with a central computer or between different
individual relays. Main components of centralized adaptive
protection system are microgrid central controller and
communication system. Main goal of adaptive protection is
to maintain settings of each relay with regard to current state
of microgrid. Microgrid central controller has module which
is responsible for periodic checking and updating relay
settings. Microgrid Central controller will monitor the state
of microgrid by polling all individual directional overcurrent
relays. Module basically consists of two components one of
which has information about the precalculated values of fault
parameters which is done during offline fault analysis of
given microgrid, second one is online operating block.
Adaptive directional interlock is used in avoiding the
nonselective operation of relays in the microgrid. Adaptive
protection is used to send the blocking signals in the right
direction so that relays on both sides of faulty element trips
and fault is isolated.
Fig. 5. Centralised Adaptive Protection System [1]
VI. CONCLUSION
Various protection issues that arise when microgrid is
integrated to main grid are discussed and analysed in this
paper. Technical challenges like change in fault current level
of the network, possibility of sympathetic tripping, reduction
in reach of distance relays, loss of relay coordination,
unintentional islanding are briefly discussed. From the fault
analysis carried out on the particular case of microgrid it is
observed that fault current level changes depending upon
modes of operation which poses the challenge while
designing protection system. Adaptive microgrid protection
system is the best solution to overcome all the problems
associated with all issues in microgrid.
APPENDIX
Distribution Transformer Parameters: - Rated apparent
power: 630 kVA, Rated voltage primary/secondary: 6000/400 V Z1t=j0.1, Z2t=j0.1,Z0t=j0.1.
Synchronous generator parameters: - Rated voltage: - 400V,
Rated
power
:160
kVA,
Z1G=j0.235,
Z2G=j0.098,Z0G=j0.027
XLPE Cable:- Nominal current :- 750 Amps, Length of cable
:- 150 meters, cable impedence ;- 0.321 ohms.
Source Impedance =j0.0126 (assumed).
[1]
REFERENCES
A.Oudalov and A. Fidigatti, “Adaptive network protection in
microgrids,” International Journal of Distributed Energy
Source, vol. 4, pp. 201–205, 2009.
[2] B.Hussain, S.Sharkh, S.Hussain, and M.Abusara,"Integration
of distributed generation into the grid: protection challenges
and solutions," 10th IET International Conference on
Developments in Power System Protection, pp. 1-5,
March/April 2010.
[3] N.D.Hatziagyriou and A.P.Sakis,"Distributed energy sources:
Technical challenges," IEEE Power Engineering Society
General meeting, 2002.
[4] H .Laaksonem and K. Kauhaneimi, “Voltage and frequency
control of low voltage microgrid with converter based DG
units,” International Journal of Integrated Energy Systems
Integrated Energy Systems, vol. 1, no. 1, pp. 47–60, June
2009.
[5] C.Stefinia, R. Lorenzo, and V. Umberto, “Analysis of
protection issues in autonomous MV microgrids,” in Proc.of
Power conversion conference ,Nagoya, 20th International
Conference on Electricity Distribution , pp. 1-5, June 2009.
[6] J.Driesen, P. Vermeyen, and R. Belmans, “Protection issues
in microgrid with multiple distribution generation units,” in
Proc.of Power Conversion Conference,Nagoya, pp. 646653,October 2010.
[7] Z.Wang, X.Huang ,and J. Jiang , “Design and implementation
of a control system for microgrid ,” in Proc. IEEE Electrical
power conference , pp.25–26, October 2007.
[8] H. Nikkhajoei and R. Lassester, “Microgrid Protection,” in
Proc.of IEEE power engineering society general meeting, pp.
1-6, June 2007.
[9] B.Kin , K. Jung , M. Choi , S. Lee ,S. Huyan , S. Kang,
“Agent based adaptive protective coordination in power
distribution system ,” in Proc.CIERD, 17th International
Conference on Electricity Distribution pp. 1–7, May. 2003.
[10] B.Hussain, S.Sharkh, S.Hussain, M.Abusara , “Impact studies
of distributed generation on power quality and protection set
up of an existing network,” International symposium on
Power Electronics, Electrical drives ,Automation and Motion,
pp. 1243-1246, March 2010.
[11] S. Conti, L. Raffa and U.Vagliasindi, “Innovative solution for
protection schemes in autonomous MV microgrids,”
International Conference on Clean Electrical Power, pp.
647–654, 2009.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Jayeshkumar G. Priolkar and Vinayak N. Shet
11
[12] S.Conti and S.Raiti, “Integrated protection scheme to
coordinate MV distribution network devices,” International
Conference on Clean Electrical Power, Nov. 2008, pp. 640–
646, 2009.
[13] E.Sortomme, S.SVenkata and J. Mitra , “Microgrid Protection
using communication assisted digital relay,” IEEE
Transactions on Power Delievery, Vol. 25 , No. 4, pp. 27892795,October 2010.
[14] A. Parsai, T.Du, A.Paqette, E.Buck, R. Harley, and D. Divan,
“Protection of meshed microgrids with communication
overlay”, Energy Conversion Congress and Exposition, pp
64-71,2010.
[15] M. Dewadasa , R. Mazumdar ,A. Ghosh and G. Ledwich ,
“Control and protection of a microgrid with converter
interfaced micro sources”, 3rd International Conference on
Power Systems, 2009.
[16] M. A. Zamani , T.S. Sidhu, and A. Yazdani "A protection
strategy and microprocessor based relay for low voltage
microgrids," IEEE Transactions on Power Delivery, Vol. 26,
No.3, pp. 1873-1883,July 2011.
[17] T.S.Ustum, C. Ozansoy and A. Zayegh, “A Microgrid
protection system with central protection unit and extensive
communication” 10th IET International Conference on
Environment and Electrical Engineering, 2011.
[18] K.Dang, X. He,D. Bi, and C. Feng “An adaptive protection
for Inverter dominated microgrid ,”International Conference
on Electrical Machines and systems, pp. 1-5, 2011.
[19] S.Ustun,C.Ozansoy,and A.Zaygeth, “A centralised microgrid
protection System for network with fault current limiters,”
10th International Conference on Environment and Electrical
Engineering, 2011.
[20] S. Conti, “Protection issues and state of art microgrids with
inverter interfaced distributed generators,” International
Conference on Clean electrical power, pp. 643-647, June
2011.
[21] H. Al-Nasseeri, M Redifern, and R.Gorman, “Protecting
microgrid systems containing solid state converter
generation”, International Conference on Future Power
System, pp.1-5, 2005.
[22] H.Zeineldin,E.Saadany,and M.Salama, “Protective relay
coordination for microgrid operation using particle swarm
optimization”, IEEE Transactions on Power Delivery, pp.
152-157,2006.
[23] W. E .Ferro , D.C. Dawson and J. Steavans, “White Paper on
Protection Issues of Microgrid Concept”, March 2006.
[24] F. Katiarei,M.R Iravani,and P.W.Lehn, “Microgrid
autonomous operation during and subsequent to islanding
process” IEEE Transactions on Power Delivery, pp. 248257,2005.
[25] N.Poaku,M.Prodanovic,andT.C.Green,
“Modelling,analysisand testing of autonomous operation of
an inverter based microgrid” IEEE Transactions on Power
Electronics pp. 613-625,2007.
[26] J.A.Pecas,C.Moreira,and A.Madureira, “Defining Control
strategies for microgrids islanded operation” IEEE
Transactions on Power Electronics pp. 916-924,2006.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Niraj Kumar Shukla and Dr. S K Sinha
12
Fuzzy and PI Controller Based Performance
Evaluation of Separately Excited DC Motor
Niraj Kumar Shukla and Dr. S K Sinha
Abstract- The separately excited dc motors with a conventional
PI speed controller are used extensively in industry. This
conventional controller can be easily implemented and are found
to be highly effective if the load changes are small however, in
certain applications, e.g., rolling mill drives or machine tools, the
drive operates under a wide range of changing load
characteristics and the system parameters vary substantially. A
conventional PI or PID controller is not preferable in these
applications.
The development of fuzzy logic controller for dc drives
in the present work is inspired by the FLC control strategy.
Broadly, two control strategies with fuzzy logic controller are
proposed for separately excited dc motor, current control and
speed control strategy. The controller is used to generate the
firing pulses. The main objective of this work is to reduce the
change in speed in transient as well as steady state region. The
aim of these proposed schemes are to improve tracking
performance of separately excited dc motor and compare with
conventional PI control strategy.
II. SEPARATELY EXCITED DC MOTOR
A separately excited dc motor is one of the most
commonly used dc motor. It is represented by equation 1.The
equivalent circuit of a dc motor armature is based on the fact
that the armature winding has a resistance Ra, a self –
inductance La, and an induced emf. This is shown in Fig.1. In
the case of motor, the input is electrical energy and the output
is the mechanical energy, with an air gap torque of Te at a
rotational speed of ωm.
Keywords— Separately excited dc motor, Proportional- Integral
(PI), Fuzzy logic controller (FLC), proportional constant (Kp)
I. INTRODUCTION
The introduction of drive system increases the automation
and productivity and also efficiency. The system efficiency
can be increased from 15 to 27 % by the introduction of
variable speed drive operation in place of constant speed
operation. A number of modern manufacturing processes,
such as machine tools, require variable speed. This is true for
a large number of applications, such as Electric propulsion,
Pumps, fan, and compressors,Plant automation ,Flexible
manufacturing systems,Robotic actuators, Cement Kilns,
Steel mills, Paper and pulp mills, Textile mills .
This paper focuses on the performance evaluation of
separately excited dc motor having P-I and fuzzy logic
controller. The simulation results are presented to
demonstrate the effectiveness of this fuzzy logic and
advantage of control system DC motor with fuzzy logic
controller (FLC) in comparison with conventional scheme.
Niraj Kumar Shukla is with Department of Electrical Engineering, SIET,
Allahabad, UP, INDIA and Dr. S K Sinha is with Department of Electrical
Engineering, Kamala Nehru Institute of Technology, Sultanpur-UP, INDIA,
Emails: niraj.knit@gmail.com, sinhask98@gmail.com
Fig. 1: Equivalent circuit of a dc motor armature
v = e + Ra ia + La (dia/dt)……….1
v = e Ra ia. ............................................2
e = K Φf ωm..........................................3
Te = Kb ia ...............................................4
Kb = K Φf volt/ (rad/sec).............5
where ωm
is rotor speed(rad/sec),v is armature
voltage, ia is armature current, La is armature inductance. Ra
is armature resistance, Kb and K are motor constants.
The principle of speed control for dc motors is developed
from the basic emf equation of the motor. Torque, flux
current, induced emf, and speed are normalized to present the
motor characteristics. Two types of control are available:
armature control and field control. These methods are
combined to yield a wide range of speed control.
Modern power converters constitute the power stage for
variable-speed dc drives. These power converters are chosen
for a particular application depending upon a number of
factors such as cost, input power source, harmonics, power
factor, noise, and speed of response.A model for the power
converter is derived for use in simulation and controller
design. Power electronic converters can be found wherever
there is a need to modify the form of electrical energy (i.e.
modify its voltage, current or frequency).
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Niraj Kumar Shukla and Dr. S K Sinha
13
Armature control has the advantage of controlling the
armature current swiftly, by adjusting the applied voltage. . If
the supply dc voltage is varied from zero to its nominal value,
then the speed can be controlled from zero to nominal or
rated value. Therefore, armature control is ideal for speed
lower then rated speed; field control is suitable above for
speed greater than the rated speed.
Motor Parameters
D.C. motor input voltage
Armature current rating
Rated speed
Armature resistance Ra
Armature Inductance La
Moment of inertia J
Viscous friction coefficient Bt
Load Torque(TL) (evaluated at steady)
Value
240 V
16 A
1220 rpm or 127.7 rps
0.5 Ω
0.01 H
0.05 kg – m2
0.02 N.m.s/rad
24.178 N-m
TABLE 1: DC Motor Parameter
These rated and evaluated parameters of motor are employed
in the simulink model.
III.CONTROLLERS FOR DC DRIVE
The schematic diagram of the dc drive system is shown in
Fig. 1. The power circuit consists of a three phase, fully
controlled bridge converter that drives a separately excited dc
motor.The thyristor bridge converter gets its ac supply
through a three phase transformer and fast acting ac
contactors. The dc output is fed to the armature of the dc
motor.The output of the current controller is the control
voltage V for the converter firing circuit. The firing pulses
c
for the SCRs are generated with a delay angle, by cosine
wave crossing method. The speed and current controllers in
Fig. 2 may be P-I controllers or fuzzy logic controllers.
Fig. 2: Speed-controller two-quadrant dc motor drive
The output of the tachogenerator is filtered to
remove the ripples to provide the signal, ω mr. The speed
command and ωr* is compared to the speed signal to produced
a speed error signal. This signal is processed through a
proportional plus integrator (PI) controlled to determine the
torque command. The torque command is limited, to keep it
within the safe current limits, and the current command is
obtained by proper scaling. The armature current command
ia* is compared to the actual armature current ia to have a zero
current error. In case there is an error, a PI current controller
process it to alter the control signal vc. The control signal
accordingly modifies the triggering angle α to be sent to the
converter for implementation.
The inner current loop assures a fast current response and
hence also limits the current to a safe preset level. This inner
current loop makes the converter linear current amplifiers.
The outer speed loop ensures that the actual speed is always
equal to the commanded speed and that any transient is
overcome within the shortest feasible time without exciding
the motor and converter capability.
The inner current loop will maintain the current at
level permitted by its commanded value, producing a
corresponding torque. As the motor starts running, the torque
and current maintained at their maximum level, the
accelerating the motor rapidly. When the rotor attains the
commanded value, the torque command will settle down to a
value equal to the sum of load torque and other motor losses
to keep the motor in steady state.
IV. FUZZY LOGIC CONTROL
Fuzzy logic is a thinking process or problem-solving
control methodology incorporated in control system
engineering, to control systems when inputs are either
imprecise or the mathematical models are not present at all.
Fuzzy controllers are used in the speed and current loops in
Fig.9, replacing the conventional P-I controllers. It is an idea
or problem-solving methodology to control non-linear
systems. The conventional control systems that work on the
basic approximation of systems to be linear systems failed
drastically when the range of application of such linear
models was increased and therefore the need of control logic
that could work even with linear systems was born. . If the
dynamics of the system and input parameters are imprecise or
missing, then fuzzy logic works by exploiting its tolerance for
imprecision of input parameters. As the father of fuzzy logic
Lofti A Zadeh puts it, “because precision is costly, it makes
sense to minimize the precision needed to perform a task.”
The applicability of fuzzy logic is indeed promising
To specify rules for the rule-base, the expert will use a
“linguistic description”; hence, linguistic expressions are
needed for the inputs and outputs and the characteristics of
the inputs and outputs. “linguistic variables” (constant
symbolic descriptions of what are in general time-varying
quantities) are used to describe fuzzy system inputs and
outputs. For our fuzzy system, linguistic variables denoted by
˜ui are used to describe the inputs ui. Similarly, linguistic
variables denoted by ˜yi are used to describe outputs yi. For
instance, an input to the fuzzy system may be described as
˜u1 = “position error” or ˜u2 = “velocity error,” and an output
from the fuzzy system may be ˜y1 =“voltage in.”
Fuzzification is an important concept in the fuzzy logic
theory. Fuzzification is the process where the crisp quantities
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Niraj Kumar Shukla and Dr. S K Sinha
14
are converted to fuzzy (crisp to fuzzy). By identifying some
of the uncertainties present in the crisp values, we form the
fuzzy values. The conversion of fuzzy values is represented
by the membership functions. In any practical applications, in
industries, etc., measurement of voltage, current, temperature,
etc., there might be a negligible error. This causes
imprecision in the data. This imprecision can be represented
by the membership functions. Hence fuzzification is
performed. Thus fuzzification process may involve assigning
membership values for the given crisp quantities.
Defuzzification is the conversion id a fuzzy quantity to a
crisp quantity, just as fuzzification is the conversion of a
precise quantity to a fuzzy quantity. The output of a fuzzy
process can be the logical union of two or more fuzzy
membership functions defined on the universe of discourse of
the output variables
Fig.5. System model with current control strategy
Fig.6: System model with speed control strategy
Fig. 3: FIS editor of fuzzy controller with 9 rule base
Fig.7: System model with current control and speed control strategy
Fig. 4: Rule viewer of fuzzy controller with 9 rule base
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Niraj Kumar Shukla and Dr. S K Sinha
Fig.8: Simulink model of plant having fuzzy controller with 3&5
rule base
15
Fig.11: Current Response for different values of Kp & Ki
RESPONSE OF DRIVE CONTROLLED BY PI SPEED
CONTROLLER
Fig.9: Simulink model of plant having fuzzy controller with 9
rule base
Fig.12: Speed Response for different values of Kp & Ki
RESPONSE OF DRIVE CONTROLLED BY PI
CURRENT CONTROLLER
Fig.13: Current Response for different values of Kp & Ki
Fig. 10: Speed Response for different values of Kp & Ki
RESULTS OF DRIVE CONTROLLED BY PI CURRENT AND
SPEED CONTROLLER STRATEGY BOTH
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Niraj Kumar Shukla and Dr. S K Sinha
Fig. 14: Speed Response for different values of Kp & Ki
16
Fig.17: Current Response for 3 rule base
It is observed that, for 3 rule base overshoot is
0.31% and settling time is 0.27 sec.
Fig.15: Current Response for different values of Kp & Ki
FUZZY CONTROLLER APPROACH
Fig.16: Speed Response for 3 rule base
Fig. 18: Speed Response for 5 rule base
Fig. 19: Current Response for 5 rule base
The result observed for 5 rule base is that, it has no
overshoot but settling time is increased from 0.27 secs to 0.40
secs.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Niraj Kumar Shukla and Dr. S K Sinha
Fig. 20: Speed Response for 9 rule base
Fig.21: Current Response for 9 rule base
The result of 9 rule base shows that overshoot is
reduced to a great extent keeping settling time to merely 0.30
sec.
17
Fig.23: Speed comparison for plants having fuzzy controller with
9 rule base vs. 5 rule base
Fig.24: Speed comparison for plants having fuzzy controller with
9 rule base vs. 3 rule base
V. RESULT ANALYSIS
Plant description
Plant with uncontrolled
rectifier
Plant having PI current
controller for kp = 3
and ki = 0.00001
Fig.22: Speed comparison for plants having fuzzy controller with 5
rule base vs. 3 rule base
Plant having PI speed
controller for kp = 12
and ki = 0.00001
Plant having PI current
& speed controller for
kpc=4,
kps=12
&
ki=0.00001
Plant having fuzzy
controller with 3 rule
base(current)
Plant having fuzzy
controller with 5 rule
base(current)
Plant having fuzzy
controller with 9 rule
base(current and speed)
Maximum
%
Overshoot
( % Mp)
Settling
Time
(ts in
secs)
Speed
regulat
ion
Current
(amp)
4.85%
0.47
1.51%
16.2
2.2
1.51%
16.19
10.10 %
0.42
0.71 %
16.14
--
0.22
0.95 %
16.18
0.31%
0.27
0.86%
16.16
0.03%
0.4
0.71 %
16.15
--
0.3
0.86 %
16.16
--
Table.2: Result analysis for different drive models
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Niraj Kumar Shukla and Dr. S K Sinha
From the table 2 above, it is observed that excellent
results are obtained by use of fuzzy controller for dc drive
system with optimum performance achieved through 9 rule
base. Overshoot can also reduced by using 5 rule base and 3
rule base but the disadvantage is that it results in increased
settling time , poor speed regulation and increased losses
when compared to fuzzy controller with 9 rule base.
The results obtained by simulation of plant with
uncontrolled converter shows poor speed regulation, settling
time and had high overshoots in transient region. In order to
reduce the maximum overshoots the uncontrolled converter is
replaced with a controlled one whose firing is controlled with
the help a PI controller. It is observed that for various values
of proportional and integral gain, the overshoots get reduced
to a great extent as compared to the plant with uncontrolled
model. On the other hand, the use of PI controller in
uncertainty association as load increases the settling time and
speed regulation are not as per desirable one. This situation is
overcome by replacement of PI controller with fuzzy logic
controller. It is observed that using fuzzy controller of
Mamdani model with 9 rule base; the maximum overshoot
gets reduced with less settling time, gives better efficiency
and better speed regulation.
VI. CONCLUSION
It is observed that fuzzy controller with Mamdani model
for 3 rule base, 5 rule base and 9 rule base can minimize the
peak overshoot ,settling time and shows better speed
regulation on contrary to conventional cases. With 9 rule
bases, a significant improvement is achieved in view of
overshoot, settling time along with better speed regulation
and better drive efficiency.
REFERENCES
[1] R.Krishnan, Electric motor drives, modeling, analysis,
and control, PHI Inc. 2003
‘Fuzzy logic with engineering
application’
Kevin M. Passino, Stephen Yurkovich, Fuzzy Control, An
Imprint of Addison-Wesley Longman, Inc., 1998
Saffet Ayasun, Gultekin Karbeyaz “DC Motor Speed
Control Methods Using MATLAB/Simulink and Their
Integration into Undergraduate Electric Machinery
Courses” Wiley Periodicals Inc. 2007.
Gilberto C. D. Sousa, Student Member, IEEE, and Bimal
K. Bose, Fellow, IEEE “A Fuzzy Set Theory Based
Control of a Phase-Controlled Converter DC Machine
Drive” IEEE TRANSACTIONS ON INDUSTRY
APPLICATIONS,
VOL.
30,
NO.
I,
JANUARY/FEBRUARY 1994.
F I W e d , A A Mabfonz, and M M lbrahim “A NOVEL
FUZZY CONTROLLER FOR DC MOTOR DRIVES”
Ninth international Conference on Electrical Machines
and Drives, Conference Publication No. 468, 0 IEE, 1999
S. Tunyasrirut, J. Ngamwiwit & T. Furuya “Adaptive
Fuzzy PI Controller for Speed of Separately Excited DC
Motor” 0-7803-5731-0/99/1999 IEEE
18
[8] Bogumila Mrozek, Zbigniew Mrozek, “Modelling and
Fuzzy Control of DC Drive”, 14-th European Simulation
Multiconference ESM 2000,
[9] Oscar Montiel1, Roberto Sepulveda , Patricia Melin,
Oscar Castillo, Miguel Angel Porta, Iliana Marlen Meza
“Performance of a Simple Tuned Fuzzy Controller and a
PID Controller on a DC Motor” Proceedings of the 2007
IEEE Symposium on
Foundations of Computational
Intelligence.
[10] Raef S. Shehata,, Hussein A. Abdullah, Fayez F. G.
Areed, “Fuzzy Logic Surge Control in constant speed
centrifugal compressors”, IEEE, 2008.
[11] C.U. Ogbuka, M.Eng. “Performance Characteristics of
Controlled Separately Excited DC Motor”. The Pacific
Journal of Science and Technology, Volume 10. Number
1. May 2009 (Spring)
Niraj Kumar Shukla received his B.Tech degree
in Electrical Engineering from B.B.D.N.I.T.M,
Lucknow, India in 2007. He obtained his M.Tech.
degree in Electrical Engineering (Power Electronics
& Drives) from KNIT, Sultanpur, U.P., India in
2010. Currently he is working as Assistant
Professor in Department of Electrical Engineering,
SIET Allahabad. His area of interest includes Fuzzy control, Power
electronics, Electric Drives and Microprocessor.
Dr. S. K. Sinha received his B.Sc.Engg degree in
Electrical from R.I.T. Jamshedpur, Jharkhand, India in
1984, and the M.Tech. degree in Electrical
Engineering from Institute of Technology,BHU,
Varanasi, India in 1987,and the Ph.D. degree from
IIT, Roorkee, India, in 1997. Currently he is working
as Professor & Head, Department of Electrical Engineering, Kamla
Nehru Institute of Technology, Sultanpur, UP, India. His field of
interest includes estimation, fuzzy control, robotics, and AI
applications.
[2] Timothy J. Ross ;
[3]
[4]
[5]
[6]
[7]
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
19
Improvement of Power System Stability Using
HVDC Controls
P. Bapaiah
Abstract: In an AC/DC power system, emergency power
actions from the HVDC connection are very important,
because appropriate fast changes in DC power will reduce the
stress on the AC system and the magnitude of the first
transient swing. An HVDC transmission link is highly
controllable. Its effective use depends on appropriate
utilization of this controllability to ensure desired performance
of the power system.
In this paper, the investigations are carried out on the
improvement of power system stability by utilizing auxiliary
controls for controlling HVDC power flow. AC/DC load flow
using eliminated variable method is utilized in the transient
stability analysis. Transient stability analysis is done on single
machine system and multimachine system, using different
control signals derived from the AC system. In this work, the
combination of the different signals, which stabilizes the
system, is found out and its effectiveness is verified.
Key words: HVDC controller, Multi machines, Stability, Power
system, load modeling.
I. High-Voltage Direct-Current Transmission
Remote generation and system inter connections lead to
a search for efficient power transmission at increasing
power levels. The increase in voltage levels is not always
feasible. The problems of AC transmission particularly in
long distance transmission, has led to the development of
DC transmission. However, as generation and utilization of
power remains at alternating current, the DC transmission
requires conversion at two ends, from AC to DC at the
sending end and back to AC at the receiving end. This
conversion is done at converter stations-rectifier at the
sending end and inverter at the receiving end. The
converters are static, using high power thyristors connected
in series to give the required voltage ratings. The physical
process of conversion is such that the same station can
switch from rectifier to inverter by simple control action,
thus facilitating the power reversal.
P. Bapaiah is currently working as an Assistant Professor in Electrical and
Electronics Engineering Department at Amrita Sai Institute of Science and
Technology, Paritala, (INDIA), Email: pagolubapaiah@gmail.com.
HVDC Transmission has advantages over AC
transmission in special situations [1]. The following are the
types of applications for which HVDC transmission has
been used:
1. Under water cables longer than about 30 km. AC
transmission is impractical for such distances
because of the high capacitance of the cable
requiring intermediate compensation stations.
2. Asynchronous link between two AC systems where
AC ties would not be feasible because of system
stability problems or a difference in nominal
frequencies of the two systems.
3. Transmission of large amounts of power over long
distances by over head lines. HVDC transmission
is a competitive alternative to AC transmission for
distances in excess of about 600 km.
Power System Stability
Power system stability is the ability of an electric power
system, for a given initial operating condition, to regain a
state of operating equilibrium after being subjected to a
physical disturbance, with most system variables bounded
so that practically the entire system remains intact [2].
The power system is a highly nonlinear system that
operates in a constantly changing environment; loads,
generator outputs and key operating parameters change
continually. When subjected to a disturbance, the stability of
the system depends on the initial operating condition as well
as the nature of the disturbance. Stability of an electric
power system is thus a property of the system motion
around an equilibrium set, i.e., the initial operating
condition. In an equilibrium set, the various opposing forces
that exist in the system are equal instantaneously or over a
cycle.
Power systems are subjected to a wide range of
disturbances, small and large. Small disturbances in the
form of load changes occur continually; the system must be
able to adjust to the changing conditions and operate
satisfactorily. It must also be able to survive numerous
disturbances of a severe nature, such as a short circuit on a
transmission line or loss of a large generator. A large
disturbance may lead to structural changes due to the
isolation of the faulted elements. At an equilibrium set, a
power system may be stable for a given (large) physical
disturbance, and unstable for another. It is impractical and
uneconomical to design power systems to be stable for
every possible disturbance [2]. The design contingencies are
selected on the basis that they have a reasonably high
probability of occurrence. Hence, large-disturbance stability
always refers to a specified disturbance scenario.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
20
The response of the power system to a disturbance may
involve much of the equipment. For instance, a fault on a
critical element followed by its isolation by protective relays
will cause variations in power flows, network bus voltages,
and machine rotor speeds; the voltage variations will actuate
both generator and transmission network voltage regulators;
the generator speed variations will actuate prime mover
governors; and the voltage and frequency variations will
affect the system loads to varying degrees depending on
their individual characteristics. Further, devices used to
protect individual equipment may respond to variations in
system variables and cause tripping of the equipment,
thereby weakening the system and possibly leading to
system instability. If following a disturbance the power
system is stable, it will reach a new equilibrium state with
the system integrity preserved i.e., with practically all
generators and loads connected through a single contiguous
transmission system. Some generators and loads may be
disconnected by the isolation of faulted elements or
intentional tripping to preserve the continuity of operation of
bulk of the system. Interconnected systems, for certain
severe disturbances, may also be intentionally split into two
or more “islands” to preserve as much of the generation and
load as possible. The actions of automatic controls and
possibly human operators will eventually restore the system
to normal state. On the other hand, if the system is unstable,
it will result in a run-away or run-down situation; for
example, a progressive increase in angular separation of
generator rotors, or a progressive decrease in bus voltages.
An unstable system condition could lead to cascading
outages and a shutdown of a major portion of the power
system.
essential to ensure satisfactory performance of the overall
AC/DC system [1].
In this paper, an attempt is made to utilize the above
advantage of HVDC systems for the improvement of
stability of the power system.
Power systems are continually experiencing fluctuations
of small magnitudes. However, for assessing stability when
subjected to a specified disturbance, it is usually valid to
assume that the system is initially in a true steady-state
operating condition.
The eliminated variable method used here [4] overcomes
these difficulties. The basic idea is to treat the real and
reactive powers consumed by the converters as voltage
dependent loads. The DC equations are solved analytically
or numerically and the DC variables are eliminated from the
power flow equations. The method is unified, since the
effect of the DC-link is included in the Jacobian. It is,
however, not an extended variable method, since no DC
variables are added to the solution vector.
Rotor angle stability refers to the ability of synchronous
machines of an interconnected power system to remain in
synchronism after being subjected to a disturbance. It
depends on the ability to maintain/restore equilibrium
between electromagnetic torque and mechanical torque of
each synchronous machine in the system. Instability that
may result occurs in the form of increasing angular swings
of some generators leading to their loss of synchronism with
other generators [2].
II.
AC/DC Load Flow
In transient stability studies it is prerequisite to do
AC/DC load flow calculations in order to obtain system
conditions prior to the disturbance. The simplest way of
integrating a DC link into the AC load flow is representing
it by constant active and reactive power injections at the two
terminal buses in the AC systems. Thus the two terminal
AC/DC buses are represented as a PQ-bus with a constant,
voltage independent active and reactive power. However
this is clearly an inadequate representation where the links
contribution to AC system reactive power and voltage
conditions is significant, since the accurate operating mode
of the link and its terminal equipment are ignored [3].
Traditionally, two different approaches have been used
to solve the power flow equations for hybrid AC/DC
systems. The first approach is the sequential method, in
which the AC and DC equations are solved separately in
each iteration. The sequential method is easy to implement,
but convergence problems may occur in certain situations.
The other approach is the unified method, in which the
solution vector is extended with the DC-variables, which
can also be referred to as extended variable method. The
drawback with the extended variable method is that it is
complex to program and hard to combine with
developments in AC power flow solution techniques.
DC System Model:
The equations describing the steady state behavior of a
monopolar DC link can be summarized as follows.
Loss of synchronism can occur between one machine
and the rest of the system, or between groups of machines,
with synchronism maintained within each group after
separating from each other.
HVDC systems have the ability to rapidly control the
transmitted power. Therefore, they have a significant impact
on the stability of the associated AC power systems. An
understanding of the characteristics of the HVDC systems is
essential for the study of the stability of the power system.
More importantly, proper design of the HVDC controls is
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vdr 
Vdi 
3 2

3 2

arVtr cos  r 
aiVti cos  i 
Vdr  Vdi  rd I d
Pdr  Vdr I d
Pdi  Vdi I d
S dr  k
3 2

arVtr I d
3

3

X c Id
X c Id
(2.1)
(2.2)
(2.3)
(2.4)
(2.5)
(2.6)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
21
S di  k
3 2

aiVti I d
(2.7)
Qdr  S dr2  Pdr2
(2.8)
Qdi  S di2  Pdi2
(2.9)
AC/DC Power Flow Equations:
When the DC-link is included in the power flow
equations, only the mismatch equations at the converter
terminal AC buses have to be modified.
Ptr  Ptrspec  Ptrac  , v   Pdr Vtr ,Vti , xdc 
Pti  Ptispec  Ptiac  , v   Pdi Vtr ,Vti , xdc 
Qtr  Qtrspec  Qtrac  , v   Qdr Vtr ,Vti , xdc 
Qti  Qtispec  Qtiac  , v   Qdi Vtr ,Vti , xdc 
computations, or if the time scale is such that the taps can be
assumed to be fixed. The modes that are obtained when
limits are encountered depend on the control strategy of the
HVDC-scheme, and this must be accounted for in the
computations. For modes B - D, ar determines  r and ai
determines the direct voltage, which normally is the case for
current control in the rectifier. For modes E - G, ar
determines the direct voltage. Subscript ‘I’ refers to constant
current control.
Table 0.1: Control modes
Control
Mode
A
(2.10)
B
(2.11)
C
(2.12)
D
(2.13)
E
where xdc is a vector of internal DC-variables. The DCvariables satisfy
R Vtr ,Vti , xdc   0
F
(2.14)
G
where R is a set of equations given by (2.1)-(2.3) and four
control specifications.
AI
BI
In the extended variable method, (2.15) is solved iteratively.

N
 P   H
 P  
 t  
 Q    J
L

 
 Qt  
 R  0 0 0 D

0

A
0

C

E

 

 

 t

 V / V 


 Vt / Vt 
 xdc 
DI
EI
(2.15)
N   



L   V / V 
FI
GI
In the sequential method, (2.14) is solved after each iteration
of (2.16).
 P   H
 Q    J
  
CI
(2.16)
Control Modes:
Seven variables and three independent equations, (2.1)(2.3), are introduced when a DC-link is included. Hence,
four specifications have to be made in order to define a
unique solution. The control modes used here are
summarized in Table 2.1, it will suffice to illustrate the
analytical elimination procedure.
Control mode A is the base case, which in the well
known current margin control corresponds to one terminal
controlling the voltage and the other the current, or
equivalently the power. The control angles and the DCvoltage are specified, and the converter transformer tap
positions are varied in order to meet these specifications.
The other modes in Table 2.1 are obtained from mode A if
variables hit their limits during the power flow
Specified
Variables
r  i
ar  i
r  i
ar  i
r  i
 r ai
 r ai
r  i
ar  i
r  i
ar  i
r  i
 r ai
 r ai
Vdi Pdi
Vdi
Pdi
ai
Pdi
ai
Pdi
ar
Pdi
Vdi Pdi
ar
Pdi
Vdi I d
Vdi
Id
ai
Id
ai
Id
ar
Id
Vdi
Id
ar
Id
The taps are assumed to be continuous variables.
Discrete tap positions can be taken into account by first
assuming continuous taps and subsequently fix the taps at
appropriate values.
The Eliminated Variable Method:
In the eliminated variable method, the equations in
(2.14) are, in principle, solved for xdc.
xdc = f(Vtr, Vti)
(2.17)
The real and reactive powers consumed by the
converters can then be written as functions of Vtr and Vti.
= Pdr(Vtr, Vti, xdc)
= Pdr(Vtr, Vti, f(Vtr, Vti))
= Pdr(Vtr, Vti)
(2.18)
It is not needed to derive explicit functions for the real
and reactive powers, only to find a sequence of
computations such that the real and reactive powers and
their partial derivatives w.r.t. the AC terminal voltages can
be computed. If all real and reactive powers are written as
functions of Vtr and Vti, (2.15) can be replaced by (2.19).
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Pdr
 P   H
 Q    J
  
N   



L   V / V 
(2.19)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
22
N '  tr , tr   Vtr
N '  tr , ti   Vti
N '  ti, tr 
N '  ti, ti 
Pdr Vtr , Vti 
Ptrac
 Vtr
Vtr
Vtr
Pdr Vtr , Vti 
Ptrac
 Vti
Vti
Vti
Pdi Vtr , Vti 
P ac
 Vtr ti  Vtr
Vtr
Vtr
Pdi Vtr , Vti 
P ac
 Vti ti  Vti
Vti
Vti
(2.20)
(2.21)
This mode occurs e.g. if the tap changer at the rectifier
hits a limit in control mode A under current control in the
rectifier. Since Pdi and Vdi are specified, Id, Vdr, Pdr and Sdi
computed as for mode A. Since αr is specified, Sdr is
computed with (2.6) instead of (2.25).
Vtr
(2.22)
 3 2

S dr
 Vtr  k
ar I d   S dr
Vtr
 

Vtr
(2.23)
L ' is modified analogously. Thus, in the eliminated
variable method, four mismatch equations and up to eight
elements of the Jacobian have to be modified, but no new
variables are added to the solution vector, when a DC-link
is included in the power flow. The partial derivatives are
those required by (2.19); ∂Pdr(Vtr,Vti)/∂Vtr, for example, is
the derivative of Pdr w.r.t. Vtr, assuming Vti is kept constant.
The DC variables, however, are not kept constant as
opposed to ∂Pdr(Vtr,Vti,xdc)/∂Vtr, which is used in (2.15).
Although (2.19) looks like (2.16), it is mathematically more
similar to (2.15). The Jacobian in (2.19) is however
normally more well-conditioned than the one in (2.15).
Analytical Elimination:
To illustrate the procedure, the analytical elimination is
carried out in detail for some representative modes. It is
sufficient to find Pd and Sd at each converter, since Qd then
can be computed with (2.8) or (2.9). The partial derivatives
for all modes in Table2.1 are shown in Table 2.2 and Table
2.3.
S dr
3 

Pdi   Rd  X c  I d2
 

k
cos  r
 k  Pdi  Pl  Ql 
Control Mode C:
[αr γi ai Pdi]
These specifications are valid e.g. if the tap changer at
the inverter hits a limit in mode A under current control in
the rectifier. Combining (2.2) and (2.5) gives
Pdi 
3 2

k
 Pdi  Ql   k  Pdi  Ql 
cos  i
ai Vti cos  i I d 
If we solve for Id, we obtain
 c1 Vti 
I d  c1 Vti 
2
I d
 c1 
Vti
where
c1 
3

X c I d2
 c2 Pdi
c12 Vti
 c1 Vti 
2
Define ∂Ii as
I i 
 c2 Pdi
(2.31)
(2.32)

(2.33)
3 Xc
Vti I d
I d Vti
(2.34)
Since Pdi is specified, both its partials are zero. Pdr is given
by (2.24), and its partial derivatives by:
Pdr
0
Vtr
P
V I
Vti dr  2 Rd I d2 ti d  2 Pl I i
Vti
I d Vti
Vtr
(2.25)
(2.26)
(2.35)
(2.36)
ai is specified, Sdi is computed with (2.7), and the
Thus, all real and reactive powers consumed by the
converters can be precomputed, and including the dc-link in
the power flow is trivial for this control mode. The same is
true for any specification of the form [αr γi x1 x2], where x1
and x2 are any two variables of [Pdr Pdi Vdr Vdi Id]. The fact
that the real and reactive powers can be precomputed for
this case is well known.
Since
Control Mode B:
Qdr and its partial derivatives are computed from (25)
[αr γi Vdi Pdi]
(2.29)
(2.30)
ai cos  i
2 Xc
c2 
Analogously, for Sdi:
S di 
(2.28)
The formulas for mode BI are essentially identical; the
only difference is that Pdi, rather than Id, is computed with
(2.5). In general, when two of the variables of [Pdr Pdi Vdr
Vdi Id] are specified, the other three can be computed from
(2.3)-(2.5).
Control Mode A:
[αr γi Vdi Pdi]
Since both the voltage and power at the inverter are
specified, the direct current can be computed with (2.5), and
Pdr can then be found by combining (2.3), (2.4) and (2.5)
Pdr = Pdi + Rd Id2
(2.24)
If we combine (2.l), (2.6) and (2.24), we obtain
Qdr S dr2

Vtr Qdr
(2.27)
partial derivatives of Qdi are given by
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vtr
Qdi
0
Vtr
(2.37)
Vti
Qdi
S2
 di 1  I i 
Vti
Qdi
(2.38)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
23
S dr
 2I i k  Pl  Ql 
Vti
Qdr
Vtr
0
Vtr
Q
2I i
 k S dr  Ql  Pl   Pl Pdr 
Vti dr 

Vti
Qdr 
Vti
(2.39)
(2.40)
(2.41)
Other Modes
The partial derivatives for the other control modes can
be derived analogously; if the tap changer controlling the
control angle is specified (modes B, D, F, G), only the
reactive power at that converter will depend on
corresponding AC voltage.
If the tap changer controlling the direct voltage is
specified (modes C, D, E, G), all the real and reactive
powers will depend on the AC voltage at that terminal.
Equations (2.30) or (2.43) are used to find the direct current
for constant power control.
If the tap changer position is specified at a converter, Sd
is computed with (2.6) or (2.7), otherwise (2.25) or (2.26)
are used. The partial derivatives for all modes in Table 2.1
are summarized in Table 2.2 and Table 2.3
Table 0.2: Partial derivatives for modes with the direct
voltage determined by ai
Pdr
Qdr Pdr Qdr
Vtr
Vti
Vti
Vtr
Vtr Vti
Vti
M
od
e
A
AI
0
0
B
0
BI
C
0
0
CI
0
D
0
DI
0
0
0
2
S dr
Qdr
2
S dr
Qdr
0
0
2
S dr
Qdr
2
S dr
Qdr
Pdi Qdi
Pdi Qdi
Vti
Vti
Vtr Vtr
Vti
Vti
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Table 0.3: Partial derivatives for modes with the direct
voltage determined by ar
M
o
de
E
Vtr
Pdr Qdr
Vtr
Vtr
Vtr
2Pl I r

0
0
2 I i
2Pl I i
Qdr
Pdi  Ql
k S dr

 Pdi  Ql 
Qdr
I i
2Pl I i
Qdr
Pdi  Ql
2
S dr


0

Pl 0 Ql 0 Pdr P0l 


k S dr0  Pdr0
 2 Pl Pdr
0

 Pdi  Ql  P
Qdr
0
dr
0
Qdi
0
Qdr
0
0
Vtr
Vtr
Qdi
Vtr
2 I r
Qdi
Pdi
Vti
Ql k S di0
0
0
Pdr  Ql
Pdr  Ql
Qdi
F
0
0
0
0
0
0
0
FI
0
0
0
0
0
0
0
0
0
0
0
Pdr  Ql
G
GI
2 Pl I r

2
S dr 1  I r  2 Pl I r Pdr
Qdr
Pdr
Ql
Pdr  QlQdr 
Qdr
0
2
S di
Qdi
Qdi
I r 
Pdr  Ql
Vtr I d
I d Vtr
I d  c3 Vtr 
0
0
Pdi0
2
S di
Qdi
2
S di
Qdi
2
S di
Qdi
2
S di
Qdi
c3 
1 I i 
c4 
(2.42)
 c3 Vtr 
2
3ar cos  r
2  Rd  3 X c 

 Rd  3 X c
 c4 Pdi
(2.43)
(2.44)
(2.45)
the analytical elimination is that the
be re-derived for other DC system
other specifications are used.
Transient Stability Studies:
Transient stability studies provide information related to
the capability of a power system to remain in synchronism
during major disturbances resulting from either the loss of
generating or transmission facilities, sudden or sustained
changes, or momentary faults. Specifically, these
Qload
l
studies provide the changes in the voltages, currents,
powers, speeds, and torques of the machines of the power
1 I i 
0
0
Pdi
Pdi  QlQdi 
Qdi
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vti
k 0S di  P0di 
I r
Qdi
Vti
∂Ir in Table 2.3 is defined as
0
Qdi
Vti
Pdi
Pdr
Ql
Pdr  QlQdr 
Qdr
Pdi A drawback with
Q

Qformulas
have to
l
Pdi  Ql di
Qdi configurations or if
2
S di
Vtr
EI
0
2
S di
Vti
2
S dr 1  I r  2 Pl I r Pdr
where
0
Pdr Qdr
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
24
system, as well as the changes in system voltages and power
flows, during and immediately following a disturbance. The
degree of stability of a power system is an important factor
in the planning of new facilities. In order to provide the
reliability required by the dependence on continuous electric
service, it is necessary that power systems be designed to be
stable under any conceivable disturbance.
The performance of the power system during the
transient period can be obtained from the network
performance equations. The performance equation using the
bus frame of reference in either the impedance or admittance
form has been used in transient stability calculations.
d
   2 f
dt
d 2 d   f


 Pm  Pe 
dt 2
dt
H
Algebraic:
E '  Et  ra I t  jxd' I t
where E’=voltage back of transient reactance
Et=machine terminal voltage
It=machine terminal current
ra=armature resistance
xd' =transient reactance
The operating characteristics of synchronous and
induction machines are described by sets of differential
equations. The number of differential equations required for
a machine depends on the details needed to represent
accurately the machine performance.
A transient stability analysis is performed by combining
a solution of the algebraic equations describing the network
with a numerical solution of the differential equations. The
solution of the network equations retains the identity of the
system and thereby provides access to system voltages and
currents during the transient period [5].
As compared with rotor long-time constants, the AC and
DC-transmission systems respond rapidly to network and
load changes. The time constants associated with the
network variables are extremely small and can be neglected
without significant loss of accuracy. The synchronous
machine stator time constants may also be taken as zero.
The DC link is assumed here to maintain normal
operation throughout the disturbance. This approach is not
valid for larger disturbances such as converter faults, DCline faults and AC faults close to the converter stations,
these disturbances can cause commutation failures and alter
the normal conduction sequence [6].
III.
Figure 0.1: Generator Classical model
Representation of Loads
Power system loads, other than motors represented by
equivalent circuits, can be treated in several ways during the
transient period. The commonly used representations are
either static impedance or admittance to ground, constant
real and reactive power, or a combination of these
representations. The parameters associated with static
impedance and constant current representations are obtained
from the scheduled bus loads and the bus voltages
calculated from a load flow solution for the power system
prior to a disturbance [5]. The initial value of the current for
a constant current representation is obtained from
SYSTEM REPRESENTATION
Generator Representation
The synchronous machine is represented by a voltage
source, in back of a transient reactance, that is constant in
magnitude but changes in angular position. This
representation neglects the effect of saliency and assumes
constant flux linkages and a small change in speed. If the
machine rotor speed is assumed constant at synchronous
speed, a normal and accepted assumption for stability
studies, then M is constant. If the rotational power losses of
the machine due to such effects as windage and friction are
ignored, then the accelerating power equals the difference
between the mechanical power and the electrical power [6].
The classical model can be described by the following set of
differential and algebraic equations:
Differential:
I po 
Plp  jQlp
E *p
The static admittance Ypo used to represent the load at bus P,
can be obtained from
Ypo 
I po
Ep
where Ep is the calculated bus voltage, Plp and Qlp are the
scheduled bus loads. Diagonal elements of Admittance
matrix (Y – Bus) corresponding to the load bus are modified
using the Ypo.
Representation of HVDC Systems
Each DC system tends to have unique characteristics
tailored to meet the specific needs of its application.
Therefore, standard models of fixed structures have not been
developed for representation of DC systems in stability
studies [1].
a) Converter model
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
25
i) Simplified model
Here valve switching is neglected and the converter is
represented by the average DC voltage equation. This model
is similar to that used in power flow analysis. The
transformer tap is assumed to be constant as the tap changer
dynamics are very slow [7]. This model is inaccurate during
severe disturbances. It cannot handle commutation failures
and cannot predict the converter behavior during
unsymmetrical faults.
ii) Detailed model
Here, the valve switching is incorporated and the model
is free from the drawbacks associated with the simplified
model. However the transient simulation of converter now
requires integration step size as small as 50 – 100 μs. This
implies heavy computation burden, so it is used only for
short duration (say 0.2 sec) immediately after the
disturbance.
b) Converter controller models
i) Response type model
The dynamics of the CEA and CC are neglected and
only the steady – state controller characteristics are
represented. The main feature of this type of controller
model is that the configuration and the parameters of the
controller are assumed to designed at a later stage basing on
the requirement.
ii) Detailed representation
It requires the analysis of actual control circuitry and the
establishment of a dynamic equivalent with a frequency
response which matches the actual controller response. This
is used along with the detailed converter model.
c) DC network model
i) Resistive network
Here DC network is represented as resistive network
ignoring energy storage elements. This approach is valid
when DC lines are short and or for back to back HVDC
links and smoothing reactors are of moderate size.
ii) Transfer function representation
For a two terminal DC link with the response type
controller, an alternative representation of the DC network
is to use a transfer function (Fig. 2.2) instead of a resistance.
In this case, the time constant T dc represents the delay in
establishing the DC current after a step change in the order
is given.
Figure 0.2: Transfer Function Model
iii) Dynamic representation
As the frequency bandwidth of the response model
considered in the transient stability studies is modest, it is
adequate to represent the dc network by a simple equivalent
circuit of the type shown in figure no 2.3. Even here, the
shunt branches may be neglected.
Figure 0.3: Equivalent Circuit
Runge-Kutta method
In the application of the Runge-Kutta fourth-order
approximation, the changes in the internal voltage angles
and machine speeds, again for the simplified machine
representation, are determined from
1
 k1i  2k2i  2k3i  k4i 
6
1
  l1i  2l2i  2l3i  l4i 
6
 it t  
it t 
i=1,2,…,no. of generators.
The k’s and l’s are the changes in  i and  i respectively,
obtained using derivatives evaluated at predetermined
points. For this procedure the network equations are to be
solved four times.
Steps of the AC-DC Transient Stability Study
Generally, the DC scheme interconnects two or more,
otherwise independent, AC systems and the stability
assessment is carried out for each of them separately, taking
into account the power constraints at the converter terminal.
If the DC link is part of a single (synchronous) AC system,
the converter constraints will apply to each of the nodes
containing a converter terminal. The basic structure of
transient stability program is given below [5]:
1) The initial bus voltages are obtained from the
AC/DC load flow solution prior to the disturbance.
2) After the AC/DC load flow solution is obtained, the
machine currents and voltages behind transient
reactance are calculated.
3) The initial speed is equated to 2  f and the initial
mechanical power is equated to the real power
output of each machine prior to the disturbance.
4) The network data is modified for the new
representation. Extra nodes are added to represent
the generator internal voltages. Admittance matrix
is modified to incorporate the load representation.
5) Set time, t=0;
6) If there is any switching operation or change in
fault condition, modify network data accordingly
and run the AC/DC load flow.
7) Using Runge-Kutta method, solve the machine
differential equations to find the changes in the
internal voltage angle and machine speeds.
8) Internal voltage angles and machine speeds are
updated and are stored for plotting.
9) AC/DC load flow is run to get the new output
powers of the machine.
10) Advance time, t=t+Δt.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
11) Check for time limit, if t ≤ tmax repeat the process
from step 6, else plot the graphs of internal voltage
angle variations and stop the process.
Basing on the plots, that we get from the above
procedure it can be decided whether the system is stable or
unstable. In case of multi machine system stability analysis
the plot of relative angles is done to evaluate the stability.
a.
Basic Control Principles
The HVDC system is basically constant-current
controlled for the following two important reasons:
 To limit overcurrent and minimize damage due to
faults.
 To prevent the system from running down due to
fluctuations of the ac voltages.
It is because of the high-speed constant current control
characteristic that the HVDC system operation is very stable
[1]. The following are the significant aspects of the basic
control system:
a) The rectifier is provided with a current control and
an α-limit control. The minimum α reference is set
at about 50 so that sufficient positive voltage across
the valve exists at the time of firing, to ensure
successful commutation. In the current control
mode, a closed loop regulator controls the firing
angle and hence the dc voltage to maintain the
direct current equal to the current order. Tap
changer control of the converter transformer brings
α with in the range of 100 to 200. A time delay is
used to prevent unnecessary tap movements during
excursions of α.
b) The inverter is provided with a constant extinction
angle (CEA) control and current control. In the
CEA control mode, γ is regulated to a value of
about 150. This value represents a trade-off
between acceptable var consumption and a low risk
of commutation failure. Tap changer control is
used to bring the value of γ close to the desired
range of 150 to 200.
c) Under normal conditions, the rectifier is on current
control mode and the inverter is on CEA control
mode. If there is a reduction in the ac voltage at
rectifier end, the rectifier firing angle decreases
until it hits the αmin limit. At this point, the rectifier
switches to αmin control and the inverter will
assume current control.
d) To ensure satisfactory operation and equipment
safety, several limits are recognized in establishing
the current order: maximum current limit,
minimum current limit, and voltage-dependent
current limit.
e) Higher-level controls may be used, in addition to
the above basic controls, to improve AC/DC
system interaction and enhance AC system
performance.
All schemes used to date have used the above modes of
operation for the rectifier and the inverter. However, there
are some situations that may warrant serious investigation of
a control scheme in which the inverter is operated
26
continuously in current control mode and the rectifier in αminimum control mode. Enhanced performance into weak
systems may be one case.
b.
Controls for Enhancement of AC System
Performance
In a DC transmission system, the basic controlled
quantity is the direct current, controlled by the action of the
rectifier with the direct voltage maintained by the inverter.
A DC link controlled in this manner buffers one AC system
from disturbances on the other. However, it does not allow
the flow of synchronizing power which assists in
maintaining stability of AC systems. The converters in
effect appear to the AC systems as frequency-insensitive
loads and this may contribute to negative damping of system
swings [1]. Further, the DC links may contribute to voltage
collapse during swings by drawing excessive reactive
power.
Supplementary controls are therefore often required to
exploit the controllability of DC links for enhancing the AC
system dynamic performance. There are a variety of such
higher level controls used in practice. Their performance
objectives vary depending on the characteristics of the
associated AC systems. The following are the major reasons
for using supplementary control of DC links:





Improvement of damping of AC system
electromechanical oscillations.
Improvement of transient stability.
Isolation of system disturbance.
Frequency control of small isolated systems.
Reactive power regulation and dynamic voltage
support.
The controls used tend to be unique to each system. To
date, no attempt has been made to develop generalized
control schemes applicable to all systems. The
supplementary controls use signals derived from the AC
systems to modulate the DC quantities. The modulating
signals can be frequency, voltage magnitude and angle, and
line flows. The particular choice depends on the system
characteristics and the desired results.
In order to augment transient stability limit large signal
modulation is used, thereby improving system security.
Large changes in the power flow in the DC link are required
to compensate for tripping of loads, generators or AC ties.
While overload capability in DC links is useful, the limits
imposed by ratings of the link usually do not curtail the
benefits of power modulation. Hence, significant
improvements can be expected out of the use of DC links in
emergency control. The rapid response of DC link
controllers makes it possible to arrest large fluctuations in
the frequency by matching generation to the load in the area
to which the DC link is connected [7]. It is desirable to
obtain control signals locally. Some of the controls that can
be used are as follows:
 Rotor frequency of adjacent generator
 Frequency at the converter bus
 Power or current in adjacent, parallel AC tie.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah

Phase angle changes in the AC system [8].
The above signals work satisfactorily for the single
machine system case. However, in the case of multimachine
system it may be necessary to employ control signals
derived from relative angle deviation, speed deviation and
acceleration and different combinations of these signals.
Apart from linear controllers, (like P, PI and PID
controllers) Fuzzy logic controllers can also be employed
which are known to give better performance. The output of
Fuzzy Logic Controller is utilized to modulate the power
order of the DC control, which in turn modulates the DC
power.
The stabilizing control is implemented through large
signal modulation of power in response to a control signal
derived from the AC system variables. The effectiveness of
the control can be enhanced by increased overload rating of
the converters which permit short – term overloads. Thus,
the rapid controllability of power in a DC link can be used
to advantage in improving the transient stability of the AC
system in which the DC link is embedded. The power flow
can even be reversed in a short time (less than 0.25sec).
Thus, DC link control can be viewed as an alternative to fast
valving or braking resistor.
IV.
Proposed Work
In this work, the advantage of fast HVDC power
modulation is utilized to improve the stability of the system
with different types of controllers and control signals.
i.
Case 1
A single machine system is considered with parallel AC and
DC transmission, having a Type – 0 Auxiliary controller and
a Proportional Integral type current controller for the HVDC
system. Here, the control signals are derived from generator
speed deviation, generator phase angle deviation and
variations of power in the parallel AC line are used and
combinations of these signals are also utilized.
ii.
Case 2
A multi machine system is considered with a HVDC link
having a Proportional Integral current controller. The
auxiliary controller is a constant gain controller which is
given with different control signals from the AC system.
The control signals are derived from relative generator
angles, relative speed variations and accelerations of
different generators.
iii.
27
Auxiliary Stabilizing Controller
A Type- 0 controller is used here and is shown in figure
4.1. By this, we can get fast response by increasing the gain
constant (Kw) or decreasing the time constant (Tw) [7]. The
gain constant (Kw) varies from 0.0 to 1.0 and time constant
varies from 0.01 to 0.1. These two constants depend on
system size and magnitude of the disturbance. Similarly this
type of auxiliary controller is tested for a single machine
AC/DC system at different gain constants (Kw) and
satisfactory results are obtained.
Figure 0.4: Type - 0 Controller
iv.
Constant Current Controller
Here Proportional Integral (PI) type controller is used
[7]. This type of controller has feedback signal (IDC) to
regulate the firing angle (Alfa) at the rectifier end to
maintain the DC link current constant and the same is shown
in figure 4.2.
Figure 0.5: Constant Current Controller
v. Test System
A single machine system connected to infinite bus
through parallel AC and DC links is considered and is
shown in figure 4.3.
Figure 0.6: Parallel AC and DC system
The single machine system, using the Type – 0 auxiliary
controller and a Proportional Integral type current controller
for HVDC link is used to demonstrate the enhancement of
stability by utilizing the controllability of the HVDC line.
The DC link is represented by a simplified transfer function
model. The following numerical data on 100 MVA base is
used.
vi.
System Data
 Generator :
Pg=3.0 pu
Xd=0.1 pu
F=50Hz
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)

H=6.0 pu
D=0.01
AC transmission lines:
Vol. 2, Issue. 1, April-2013.
P. Bapaiah



28
Xeq = 0.15 pu
Transformer:
Xt=0.05 pu
DC link:
K1=0.4 K2=0.3 Tw=0.05
Ld=0.03 Rd=0.05 Xc=0.126
Initial conditions
δ=0.6435
Δw =0
Id=0.8957
Alfa=0.279
Vdi=0.99
0.95
del
0.9
0.85
)
d
ra
l(
e
d
0.8
0.75
0.7
0.65
The analysis is performed using the disturbances like
variations in mechanical power (0.3 pu) and outage of one
of the parallel AC lines. The stability of the system is
enhanced utilizing different stabilizing signals for power
modulation in the HVDC link.
vii. Case A: Mechanical Power Variations
The mechanical power of the generator is increased by
0.3 pu and different control signals from the AC system are
utilized for the stability improvement. Without any external
control signal applied to the HVDC system the stability
analysis is performed and the generator angle plot is as
shown in figure no. 4.4. Considering variations in speed and
parallel AC tie power variations different control signals are
applied to HVDC controller. The plots of phase angles of
generator for different stabilizing signals are shown in
figures 4.5 – 4.9.
0
2
4
6
time(sec)
8
10
12
Figure 0.8: Plot of Generator angle with Δw as the auxiliary
stabilizing signal (Kw= 1.4)
0.95
del
0.9
0.85
)
d
a
r
l(
e
d
0.8
0.75
0.7
0.65
0.95
0
del
2
4
6
8
10
12
time(sec)
14
16
18
20
Figure 0.9: Plot of generator angle with ΔPac (change in
power of adjacent AC line) as the auxiliary stabilizing signal
(Kw= 0.1).
0.9
0.85
1
0.8
del
d)
ar
(l
e 0.75
d
0.95
0.7
0.85
0.9
)
d
ra
(l
e
d
0.65
0
2
4
6
time(sec)
8
10
12
Figure 0.7: Plot of Generator angle without any external
control signal applied
0.8
0.75
0.7
0.65
0
2
4
6
8
10
12
time(sec)
14
Figure 0.10: plot of generator angle with
auxiliary stabilizing signal (Kd=0.45).
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
16
18
20
d   
as the
dt
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
29
0.649
1
del
0.95
del
0.648
Kd=0.12,Kp=1.4
0.647
0.9
0.646
0.85
)
d
a
r(
l
e
d
0.645
)
d
ra
l(
e
d
0.8
0.75
0.644
0.643
0.642
0.7
0.641
0.65
0.64
0.639
0
2
4
6
time(sec)
8
10
12
Figure 0.11: Plot of generator angle with Kp* Δw
+Kd*
d   
as the auxiliary stabilizing signal (Kp=1.4,
dt
0
2
4
6
time(sec)
8
10
12
Figure 0.13: Plot of generator angle without any external
control signal.
0.647
del
0.6465
Kd =0.12).
0.646
0.6455
1
del
0.95
)
d
ra
l(
e
d
Kd=0.12,Kp=1.4,Ki=0.04
0.9
0.645
0.6445
0.644
0.85
)
d
ra
(l
e
d
0.6435
0.8
0.643
0.75
0.6425
0
2
4
0.7
8
10
12
Figure 0.14: plot of generator angle with Δw as the auxiliary
stabilizing signal (Kw=4.5).
0.65
0
2
4
6
8
10
12
time(sec)
14
16
18
20
0.647
Figure 0.12: plot of generator angle with Kp* Δw
+Kd*
6
time(sec)
del
0.6465
d   
+KiΔδ as the auxiliary stabilizing signal
dt
0.646
0.6455
(Kp=1.4, Kd =0.12, Ki=0.04).
viii. Case B: Line Outage
One of the parallel AC lines is given outage, here the
two ac lines are assumed to be similar. Therefore this
disturbance can be reflected by varying the value of X eq,
which represents the equivalent reactance of both the lines.
Here, once again the different signals are utilized for
stability improvement. The plots of generator angles for
different stabilizing signals are shown in figures 4.10 – 4.15.
)
d
a
r(
l
e
d
0.645
0.6445
0.644
0.6435
0.643
0.6425
0
2
4
6
8
10
12
time(sec)
14
16
18
20
Figure 0.15: plot of generator angle with ΔPac (change in
power of adjacent AC line) as the auxiliary stabilizing signal
(Kw=2).
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
30
b. Multimachine System Analysis
The power flow through a HVDC link can be highly
controllable. This fact is utilized to strengthen the power
system stability. The WSCC – 9 Bus system is considered
for the stability analysis and is given in the figure 4.16.
0.649
del
0.648
0.647
0.646
)
d
ra
l(e
d
0.645
0.644
0.643
0.642
0.641
0
2
4
6
time(sec)
8
10
Figure 0.16: plot of generator angle with
auxiliary stabilizing signal (Kd=1).
12
d   
as the
dt
0.647
del
Figure 0.19: WSCC 9 Bus System
0.6465
0.646
0.6455
)
d
ra
l(
e
d
0.645
0.6445
0.644
0.6435
0.643
0.6425
0
2
4
6
time(sec)
8
10
12
Figure 0.17: plot of generator angle with Kp* Δw
+Kd*
d   
as the auxiliary stabilizing signal (Kp=4.5,
dt
Kd =0.5).
0.647
del
0.6465
0.646
The scenario adapted for our study is given below:
A fault is assumed to occur on Line 4-6, at initial time
zero. It is assumed that a grounded fault occurred near to
Bus 6 and the line from Bus 4 to Bus 6 is removed after 4
cycles. The HVDC line is located between buses 4 –5.
Under these conditions, the impact of HVDC on system
stability is presented. Initially, a case in which the HVDC
line maintains the same control as in the normal state, in
which the post-fault HVDC power flow setting remains the
same as before, is investigated. It was found that, the system
becomes unstable. Then a PI controller is designed to
stabilize the system. The controls are used to alter power
flow setting in the HVDC line. The system data is given in
appendix I.
i. Case I: Uncontrolled Case
Fig. 4.17 is a plot of the generator angles for a grounded
fault at Bus 6. The HVDC line is in between buses 4 – 5.
The post fault power flow setting through the HVDC line is
the same as the pre-fault power flow setting. No extra
control mechanism has been employed here. The plot of
relative angles of the generator is shown in figure 4.18.
4
0.6455
)
d
ra
l(
e
d
6
0.645
x 10
5
0.6445
4
0.644
3
0.6435
)
g
e
d
l(
e
d
0.643
0.6425
0
2
4
6
time(sec)
8
10
12
Figure 0.18: Plot of generator angle with Kp* Δw
+Kd*
d   
+KiΔδ as the auxiliary stabilizing signal
dt
(Kp=1.4, Kd =0.12, Ki=0.0005).
del1
2
1
0
del2
del3
-1
-2
0
5
10
15
time(sec)
20
25
30
Figure 0.20: Plot of generator angles without any extra
control
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
31
Integral of error, I (t), is found out by trapezoidal method.
The time interval [0, t] is divided into n time steps with an
interval of Δt. Here k is the Kth time step, ek=error at time
step k and Δt= time step interval (=1/50). Accordingly,
for k = 1:n
4
8
x 10
7
6
I k  I k 1 
5
4
)
g
e
d
(l
e
d
t
I k   e  t  dt
2
(4.4)
0
1
The plot of relative angles of the generators is as shown in
figure 4.19 and the plot of generator phase angles is shown
in figure 4.20.
del23
0
-1
(4.3)
With initial conditions, e0 =0, I0 = 0, and
del13
del12
3
1
ek  ek 1  t
2
0
5
10
15
time(sec)
20
25
30
500
Figure 0.21: Plot of relative angles with no extra control
From Fig 4.17, it can be seen that angle of generator 1
goes unsynchronized from those of generators 2 & 3. In
order to make the angle of generator 1, to be in step with
those of the other two generator angles, the power mismatch
at Bus 1 has to be altered. This can be achieved by changing
the power flow in the HVDC line through an augmented
feedback control.
kp=0.0013,
ki=0.00061
400
del13
300
)
g
e
(d
l
e
d
200
del13
100
del23
When employing a feedback loop, the error signal is defined
to average out the acceleration force for all the three
machines as follows [9]:
 P _ mis  3 P _ mis  2  



H
3
H  2    p _ mis 1 



e

 (4.1)

  H 1 
2




0
-100
5
10
15
time(sec)
20
25
30
Figure 0.22: Plot of relative angles with PI control
4
4
x 10
3.5
where,
P_mis(i) = Real Power Mismatch at Bus ‘i’
H(i) = Moment of Inertia of generator ‘i’.
HVDC system’s current controller and line dynamics are not
considered in this analysis. Accordingly, a realistic simple
model for HVDC is adopted in the stability calculations.
The extra energy introduced by the fault will be eventually
smoothed out by an AGC as long as the machines are kept
synchronized.
0
3
2.5
)
g
e
d
l(
e
d
2
1.5
1
kp=0.0013,
ki=0.00061
0.5
ii. Case II: With PI Controller
System stability was augmented using a PI Controller. The
control mechanism employed is given below [9]. Based on
the error signal defined above, the flow in the DC line is
changed as follows:
where,
Pdik 1  Pdik  K p e k  K i  e  t  dt
(4.2)
Pdi = Active Power flow at the Inverter terminal.
K=Time step.
e= Error signal.
Kp=Proportional constant (=0.0013).
Ki= Integral constant (=0.00061).
0
0
5
10
15
time(sec)
20
25
30
Figure 0.23: Plot of Generator angles with PI control
c.Multimachine
System
Considering
Current
Controller and Line Dynamics
Now considering the dynamics associated with the current
controller and the DC line the stability study is performed
again. The DC line is represented by the transfer function
model.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
32
i. Current Controller
Here, proportional integral current controller is used and
is shown in figure 4.21
4
x 10
10
K1=0.0006, K2=0.003
8
6
del12
)g
e
d
(l
e
d
4
del13
2
del23
0
Figure 0.24: Current controller
-2
ii. Auxiliary controller
Here, a simple constant gain Auxiliary controller is
employed and is shown in figure 4.22. The stability of the
system is improved by varying the gain constant (Kw) of the
above controller.
0
5
10
15
time(sec)
20
25
30
Figure 0.27: Plot of relative angles without any external
control signal
It is clearly seen that the system is becoming unstable,
generator 2 and generator 3 are moving together whereas
generator 1 falling out of synchronism, with this group.
Considering the following signals:
2 1 3 1

error1  
  2 3 (4.5)
2



del2del1del3del1
error2 
del2del3(4.6)
2


Figure 0.25: Constant Gain Controller
iii. Case 1 Uncontrolled case
Considering the same disturbance as in previous case,
stability study is performed again. Here two extra
differential equations representing the current controller and
the HVDC Line dynamics are to be solved using the Runge
– Kutta method. Here the taps are assumed to be constant
and the mode shifts are not considered [1]. Without any
extra control mechanism the plots of generator angles and
their relative difference will be as shown in figure 4.23 and
figure 4.24.
4
6
x 10
5
 P _ mis  3 P _ mis  2  



H  3
H  2    P _ mis 1  (4.7)
error3  



  H 1 
2




The signal error1, represents average error in the speed
differences between the three generators. The signal error2,
represents average error in relative angles between the three
generators. The signal error3 is defined to average out the
acceleration force for all the three machines. Different
combinations of the above three signals are considered, in
order to improve the stability.
iv. Case 2
Considering the signal error3 as the control input, the
plot of relative angles is as shown in the figure no 4.25.
4
del1
3
2
)
g
e
d
l(
e
d
1
0
del2
-1
-2
del3
-3
-4
0
5
10
15
time(sec)
20
25
30
Figure 0.26: Plot of generator angles with no external
control signal applied
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
33
200
Fig 4.27 Plot of relative angles with error1 and error3 as control signals
150
K1=0.005, K2=0.002,
Kp=0.2, Kd=0.08
del13
0
del23
100
-200
del13
del12
del12
50
-400
)
g
e
(d
l
e
d
)
g
e
d
(l
e
d
-600
0
-800
del23
-50
-1000
-1200
0
5
10
15
time(sec)
20
25
-100
30
Figure 0.28:Plot of relative angles with error3 as the control
signal
v. Case 3
Considering the combination of error1 and error2 signals as
the control input, the plot of relative angles is as shown in
figure no 4.26.
10
15
time(sec)
20
25
30
vii.
Case 5
Considering the combination of error2 and error3 signals to
generate the control signals, the plot of relative angles will
be as shown in figure no 4.28.
Fig 4.28 Plot of relative angles with error2 and error3 as control signals
80
del13
del13
60
del12
40
40
del23
20
20
0
)
g
e
l(d
e
d
-20
0
del23
-20
-40
-40
-60
K1=0.0065, K2=0.013,
Kp=1.5, Ki=2
-80
-60
-80
5
Figure 0.30: Plot of relative angles with error1 and error3 as
control signals
60
)
g
e
d
(l
e
d
0
K1=0.0002, K2=0.0008,
Kp=0.001, Ki=15
0
2
4
6
-100
8
10
time(sec)
12
14
16
18
Figure 0.29: Plot of relative angles with error1 and error2 as
control signals
vi. Case 4
Considering the combination of error1 and error3 signals
to generate the required control signal, the plot of relative
angles will be as shown in the figure no 4.27.
0
2
4
del12
6
8
10
12
time(sec)
14
16
18
20
Figure 0.31: Plot of relative angles with error2 and error3 as
control signals
viii.
Case 6
Considering the combination of all the three signals to
generate the control signal, the plots of the relative angles
with different gains are as shown in figure (4.29) and figure
(4.30).
100
K1=0.0006, K2=0.003,
Kp=2.5, Ki=0.01, Kd=0.3
80
60
)
g
e
d
(l
e
d
del13
40
20
0
del12
del23
-20
-40
0
5
10
15
time(sec)
20
25
30
Figure no 0.32: Plot of relative angles with PID controller.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P. Bapaiah
34
100
References
K1=0.0006, K2=0.003,
Kp=2.5, Ki=0.02, Kd=0.2
80
[1]
60
del13
)
g
e
l(d
e
d
40
20
0
del23
del13
-20
-40
0
5
10
15
time(sec)
20
25
30
Figure 0.33: Plot of relative angles with PID controller
The study reveals that the system can be stabilized by using
a controller which produces the control signal given in
equation 4.8.
Control signal, error = Kp*error1+ Ki*error2 +
Kd*error3
(4.8)
Here the signal error2 is the equivalent to the integral of the
signal error1, and the signal error3 is equivalent to the
differential of the signal error1. Hence, the controller
proposed above is equivalent to a PID controller. Then the
control signal can be equivalently represented as in equation
4.9.
error= Kp e(t)+Ki Ie(t)+Kd De(t)
(4.9)
Considering this, the methodology used in variable gain
PID controller scheme can be applied to the above
controller, to improve its performance. In the next chapter, a
Fuzzy PID controller scheme is proposed to improve the
stability of the system.
V. CONCLUSIONS
For the variations in the mechanical power of the
generator, in the single machine system, the speed change
signal as a control signal is more effective as shown in
figures 4.5 to 4.9. For a parallel line outage, the variation in
power, in the other parallel line, when used as the control
signal, gives better performance as shown in figures 4.10 to
4.15.
When the HVDC current controller and line dynamics
are not considered, the transient stability of the
multimachine system after the occurrence of the specified
fault, is improved by using a PI controller with average
acceleration as the control signal, as shown in figure 4.19
P. Kundur, “Power System Stability and Control”, McGrawHill, Inc., 1994.
[2] Prabha Kundur, John Paserba, “Definition and Classification
of Power System Stability”, IEEE Trans. on Power Systems.,
Vol. 19, No. 2, pp 1387- 1401, May 2004.
[3] A. Panosyan, B. R. Oswald, “Modified Newton- Raphson
Load Flow Analysis for Integrated AC/DC Power Systems”,
[4] T. Smed, G. Anderson, “A New Approach to AC/DC Power
Flow”, IEEE Trans. on Power Systems., Vol. 6, No. 3, pp
1238- 1244, Aug. 1991.
[5] Stagg and El- Abiad, “Computer Methods in Power System
Analysis”, International Student Edition, McGraw- Hill,
Book Company, 1968.
[6] Jos Arrillaga and Bruce Smith, “AC- DC Power System
Analysis”, The Institution of Electrical Engineers, 1998.
[7] K. R. Padiyar, “HVDC Power Transmission Systems”, New
Age International (P) Ltd., 2004.
[8] “IEEE Guide for Planning DC Links Terminating at AC
Locations Having Low Short-Circuit Capacities”, The
Institute of Electrical and Electronics Engineers, Inc., 1997.
[9] Garng M. Huang, Vikram Krishnaswamy, “HVDC Controls
for Power System Stability”, IEEE Power Engineering
Society, pp 597- 602, 2002.
[10] Choo Min Lim, Takashi Hiyama, “Application of A RuleBased Control Scheme for Stability Enhancement of Power
Systems”, pp 1347- 1357, IEEE 1995.
P. Bapaiah received Diploma in Electrical
and
Electronics
Engineering
from
A.A.N.M&V.V.R.S.R
Polytechnic,
Gudlavalleru (INDIA) in 2002. Received his
Bachelor degree in Electrical and Electronics
Engineering from Gudlavalleru Engineering
College,
Gudlavalleru
(INDIA)
in
2006.Worked as Site Engineer in MICRON Electricals at
Hyderabad in 2006-2008. And M.Tech in Power Systems
Engineering from V.R.Siddhartha Engineering College,
Vijayawada, Acharya Nagarjuna University Guntur, (INDIA) in
2010. He is currently working as an Assistant Professor in
Electrical and Electronics Engineering Department at Amrita Sai
Institute of Science and Technology, Paritala, (INDIA). His
research interests include Power Systems, HVDC Transmission
Systems, and Power Quality.
Considering the HVDC current controller and line
dynamics, it is observed that the transient stability of the
multimachine system is improved only if the combination of
all the three signals derived from relative speed, phase angle
and average acceleration are used, as shown in figures 4.23
to 4.30. This paper demonstrates that, control mechanisms
can be designed and incorporated for HVDC power
modulation, to augment the stability of the power system.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Sourabh Jain, Shailendra Sharma and R.S. Mandloi
35
Improved Power Quality AC Drive Feeding
Induction Motor
Sourabh Jain, Shailendra Sharma and R.S. Mandloi
Abstract: This paper deals with the power quality enhancement
of induction motor drive used to operate in vector controlled
mode. The improved power quality AC drive consists of voltage
source converter (VSC), voltage source inverter (VSI) and an
intermediate DC bus supported with capacitors. The
performance of improved power quality AC drive is
demonstrated on developed simulation model. The obtained
result verifies performance of improved power quality AC drive
in all four quadrants.
Keywords: PWM Rectifier, Indirect Vector Control Drive, Unit
template (UTT), Regenerative operation
NOMENCLATURE
Rr
Lr
Lm
ids
iqs
idr
iqr
∗
∗
Ψ
Ψ
Vref
VDC
Vabc
Ua Ub Uc
Ia, Ib, Ic
Rotor resistance(referred to rotor side )
Rotor leakage Inductance
Magnetizing Inductance
Magnetizing component of stator current
Torque component of stator current
d-axis rotor current
q-axis rotor current
Reference magnetizing component of stator
current
Reference Torque component of stator current
d-axis rotor flux linkage
q-axis rotor flux linkage
Rotor flux
Rotor frequency (rad/s)
Electrical frequency (rad/s)
Slip frequency (rad/s)
Rotor mechanical speed
Reference Speed
Base Speed
Rotor angle
Angle of synchronously rotating frame
Slip angle
Reference voltage
Intermediate DC voltage
Three Phase Supply Voltage
Unit template of Phase a,b,c
Three phase stator current
I. INTRODUCTION
The squirrel cage induction motor is most versatile in
industry due to its less maintenance, cheap in cost and rugged
in construction [1]. Due to its constant speed characteristics,
it is not inherently considered as suitable choice for
applications which needs variable speed operation [2]. There
have been many control techniques reported in literature
which facilitates variable speed operation namely V/f control,
vector control and direct torque control (DTC) [3]. The V/f
control technique allows the induction motor to deliver its
rated torque at speed up to its rated speed, beyond the rated
speed, its torque capability is declined [4]. However with this
control technique the performance under transient condition
is inferior. Vector control technique allows a squirrel-cage
induction motor to drive with high dynamic performance. It
provides a decoupling of two components of stator current:
one producing the airgap flux and the other producing the
torque. Therefore, it allows independent control of torque
and flux, which is similar to a separately excited dc machine
[3]. In Indirect vector control, field angle has been obtained
by using rotor position measurement and partial estimation of
machine parameters [2]. The magnitude and phase of the
stator currents has been controlled in such a way that flux
and torque components of current remain decoupled under
dynamic and static conditions [3]. Moreover in many
applications such as conveyors, trolleys, electric vehicles,
locomotives, traction etc. it is required to achieve fast
dynamic response in all four quadrant namely forward
motoring, forward braking, reverse motoring and reverse
braking. In commercial available drives mostly diode bridge
rectifier has been used to convert AC into constant voltage
DC which creates problem such as ‘poor power factor’,
‘highly discontinuous current’, ‘injection of harmonics into
AC mains’ and ‘fluctuations of dc link voltage’ [5]. This
paper deals with a four quadrant improved power quality
induction motor drive using a voltage source inverter (VSI)
and a voltage source converter (VSC) with intermediate DC
link.
Sourabh Jain, Shailendra Sharma and R.S. Mandloi are with Department
of Electrical engineering, SGSITS, Indore, M.P., India, Emails:
jain.sourabh85@gmail.com,
ssharma.iitd@gmail.com,
ravindrasmandloi@yahoo.com
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Sourabh Jain, Shailendra Sharma and R.S. Mandloi
36
Fig.1 Block Diagram of IFOC induction motor drive
II. SYSTEM CONFIGURATION
The system under consideration is shown in Fig.1.The
insulated gate bipolar transistor (IGBT) based VSI is
controlled using the indirect vector control. It also consists of
three phase VSC. The VSC and VSI shares common DC
link. The intermediate point of each-leg of a VSC is
connected to input supply through an interface inductor. A
star connected high pass filter is used at VSC terminals to
absorb switching ripples. Similarly midpoint of each leg of
the VSI is connected to star connected three-phase induction
motor. Parameters of proposed system are given at appendix
1 2.
The rotor current equations can be obtained by putting
Eq.(5)-(6) in eq. (1)-(2) as
Ψ
Ψ −
+
−
Ψ =0
Ψ
+
Ψ
−
Ψ
=0
Where
=
−
The rotor flux linkage equation as,
Ψ =
+
Ψ
=
+
Eq. (3)-(4) can be rearranged as,
1
= Ψ −
=
1
Ψ
−
(2)
+
For decoupling control
Ψ =0
Ψ
=0
Ψ
−
Ψ
(8)
=0
So that the total rotor flux Ψr is directed on de-axis
+
III. CONTROL SCHEME
A. VSI Control
The VSI is controlled using indirect field orientation
control (IFOC), which is also known as flux feed-forward
control. Block diagram of IFOC technique shows in Fig.2.
IFOC is derived from dynamic equation of induction motor,
unit vector signals are generated in feed forward manner. The
stator phase current serves as input, hence the stator
dynamics can be neglected. The rotor equation containing
flux linkage as a variable given as
(1)
+
+
=0
−
(7)
(9)
=
From the q-axis current components and slip gain, the slip
speed relation is obtained as:
∗
(10)
= ∗ =
,
=
=
The slip speed, together with the feedback rotor speed, is
integrated to obtain the stator reference flux linkage space
vector position
(11)
=
= (
+ ) =
+
The actual rotor speed and sensed rotor speed is compared.
Speed error acts as input to proportional integral (PI)
controller, which provides a torque controlling current
component ∗ of the stator current. This current component
is used to regulate the torque along with the slip speed. The
output of the PI controller is given as:
(12)
∗
= Δ +
Δ
(3) Similarly the flux producing current component ∗ , is
obtained from the stator flux linkage reference value and
(4) given by the following equation,
(13)
∗
=
Ψ∗
(5) with
∗
= k Ψ∗
(6)
∗
=k
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Ψ∗
if 0 ≤
otherwise
≤
>
Vol. 2, Issue. 1, April-2013.
Sourabh Jain, Shailendra Sharma and R.S. Mandloi
The flux reference is constant till the reference rotor speed
below its rated speed, but if motor runs above rated speed,
flux weakening essential.
37
=
,
=
2 2 2 2
Va Vb Vc
3

,
(15)
=


Fig.2
Block diagram of control of VSI
B. Control of VSC
The block diagram of control algorithm used for a front
end VSC is shown in Fig.3. The control scheme ensures
constant DC bus voltage and unity power factor at supply
sides even under change in load. The reference DC link
voltage (Vref) is compared with the actual DC link voltage
and error voltage is proceed through a PI controller, the
voltage controller output is multiplied by the in phase unit
template of each phase. These reference currents are
compared with sensed currents and the error signals are used
as input to a PWM modulator which provides pulses for the
VSC [10]. The amplitude of phase voltage is obtained as,
(14)
2
( +
=
+ )
3
The in-phase template are derived as
Fig.3
Block diagram of control of VSC
IV.
MATLAB-BASED SIMULATION
The improved power quality AC drive for induction
motor is modeled in MATLAB using Power System
Blockset. Fig. 4 depicts the setup used to estimate the
performance of the AC drive with proposed control scheme
through simulation. The source block connected with a threephase voltage source active rectifier block. Three leg IGBTs
based VSC, capacitive filter and input side inductive filter
used as an active rectifier. The performance of the drive is
controlled by IFOC controlled VSI. Effectiveness of
proposed system improved by VSC at supply sides.
Fig.4 Simulation model of IFOC control induction motor drive
V. SIMUALTION RESULTS
Results are obtained on developed simulation model to
demonstrate the performance in the steady state and transient
condition shown in Figs.4 to 6. The parameters used in
simulation are given appendix 1 2.
A. Performance of System During Starting mode
Fig.5 shows the simulation results during motoring condition
without load applied. At start, rated current is observed to
accelerate the motor. After that current is settled. At time
350ms, a 25N-m load is applied on motor. The dc link
feedback controller acts to keep dc link voltage at its
reference value.
B. Performance of System on Braking mode
Till during time, 0 to 500ms AC drive runs in motoring
mode, the fundamental input current is in phase with supply
voltage. After this time interval, braking is applied on motor.
During this time VSC DC link current (Idc-recti) is divided
into two components i.e. capacitor current (Idc-capa) and
output current (Idc- o/p) which fed into VSC. The observed
results are shown in Fig.6.
C. Regenerative Braking mode
At time t4=1.0 sec. the motor reference speed should be
negative. Rotor rotates at opposite direction. Small
fluctuation is found in DC link voltage. After time t =1.32
sec. The reference speed is changed negative to zero and
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Sourabh Jain, Shailendra Sharma and R.S. Mandloi
regenerative braking is applied on motor. In this mode,
supply currents are fed to the source, variations in currents
are shown in Fig.7. VSC currents are observed negative.
38
Zero speed tracking error is achieved during steady-state
conditions
and
with
reference
speedvariation.
Fig.5 Simulation results: Motoring mode
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Sourabh Jain, Shailendra Sharma and R.S. Mandloi
39
template algorithm has been developed for control of VSC.
The performance of developed AC drive has been
demonstrated under starting, motoring and braking modes
and it is found satisfactory.
VII. APPANDIX
THREE PHASE INDUCTION MOTOR
PARAMETER
Rated Power = 7.5 kW
Rs=0.7384Ω
Rated voltage = 415V
Rr′ = 0.7402Ω
Rated current = 14.5A
Ls=0.003045H
Rated Speed Ns =1450r/min
Lr=0.003045H
Frequency f = 50Hz
Lm = 0.1241H
Poles Pair p = 2
J = 0.0343 kg.m2
Friction Factor(F) =0.000503 N.m.s
Kp = 6.28
Ki = 0.96
1.
2.
VOLTAGE SOURCE CONVERTER(VSC)
PARAMETER
Supply Voltage = 415V
Line Impedance Rs= 0.5 Ls= 5mH
Frequency = 50Hz
Filter Rf = 5Ω C f = 20µF
Fig.6 Simulation results: Braking mode
DC bus capacitance = 7500 µF
Switchs(Sw1 – Sw6) = IGBTs
Kp = 0.36
Ki = 3.2
REFERENCES
[1] Bimal K Bose, Modern Power Electronics and AC Drives,
Pearson education
[2] R.Krishan, Electric motor drives modeling, analysis &
control, PRENTICE HALL
[3] P. C. Sen, “Electric Motor Drives and Control-Past, Present,
Fig.7 Simulation results: plugging and regenerative braking
VI. CONCLUSION
An improved power quality induction motor drive has been
modeled and simulated. A three leg voltage source converter
(VSC) and a voltage source inverter (VSI) has been used to
develop four quadrant induction motor drive. An indirect
vector control has been used for controlling a VSI. A unit
and Future” IEEE Transactions on Industrial Electronics, Vol.
37, No. 6, December 1990
[4] N.Mohan, T.M.Undeland, and W.P.Robbins, Power
Electronics, John Wiley, Newyork,1995
[5] Singh B. ; Singh B.N. ; Singh B.P. ; Chandra, A. ; AlHaddad, K., “Unity Power Factor Converter-Inverter Fed
Vector Controlled Cage. Motor Drive without Mechanical
Speed Sensor”, IEEE Conference Publications 1995
[6] J Vithayathil, Power Electronics: principles and applications,
McGraw-Hill, Newyork , 1995
[7] H Akagi, “New trends in active Filters for power
conditioning”, IEEE Trans.on Ind. Appl., 1996, 32, pp. 1312–
1322
[8] Lipo T.A., “Recent progress in the development of solid-state
ac motor drives”, IEEE Trans, on Power Electronics, Vol.3,
No.2, pp.105-117, Jan. 1988.
[9] Bose B.K., “Evaluation of modern power semiconductor
devices and future trends of converters”, IEEE Trans, on
Industry
Applications,Vol.IA-28,
No.2,
pp.403-413,
March/April 1992.
[10] Mika Salo, Heikki Tuusa “A Vector-Controlled PWM
Current-Source-Inverter-Fed Induction Motor Drive With a
New Stator Current Control Method” IEEE Transactions on
Industrial Electronics, Vol. 52, No. 2, April 2005
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Sourabh Jain, Shailendra Sharma and R.S. Mandloi
40
[11] E.W.Gunther and H.Mehta, “A survey of distribution system
power quality” ,IEEE Trans. On Power Delivery, vol.10, No.1,
pp.322-329, Jan.1995.
[12] José R. Rodríguez, Juan W. Dixon,José R. Espinoza,Jorge
Pontt, and Pablo Lezana, “PWM Regenerative Rectifiers:
State of the Art” IEEE Trans. on Industrial Electronics, Vol.
52, No. 1, February 2005
[13] Brod D.M. and Novotny D.W., "Current control of VSI-PWM
inverters", IEEE Trans, on Industry Applications, Vol. IA- 21,
No.3, pp.562-570, May/June 1985.
[14] J. Rodríguez, L. Morán, J. Pontt, J. Hernández, L. Silva, C.
Silva, and P. Lezana, “High-voltage multilevel converter with
regeneration capability,” IEEE Trans. Ind. Electron., vol. 49,
no. 4, pp. 839–846, Aug. 2002.
[15] H. Fujita and H. Akagi, “The unified power quality
conditioner: the integration of series- and shunt-active filters,”
IEEE Trans. Power Electron.,vol. 13, no. 2, pp. 315–322, Mar.
1998.
[16] Singh B.N., Singh Bhim and Singh B.P., “Performance
analysis of closed loop field oriented cage induction motor
drive”, Journal of Electric Power Systems and Research,
Vol.29 No.2, pp.69-81, Feb.1994.
[17] Vas Peter, “Vector Control of AC Machines", Clarendon Press
Oxford, 1990.
[18] F. Blashke, “The principle of field-orientation as applied to the
new transvector closed-loop control system for rotating field
machines,” Siemens Rev., vol. 34, no. 5, pp. 217–220, 1972.
[19] Huang, M.S.; Liaw, C.M. “Improved field weakening control
for IFO induction motor” IEEE Transactions on Aerospace
And Elecronic Systems, Vol. 39, No. 2 pp. 647-659 April
2003
[20] P. Farmanzadeh, “A robust controller design to stabilize
induction motor drive operation using (IFOC) method” in
Proc. IEEE PEDSTC, 2012, pp. 218 - 222
[21] E. Etien, C. Chaigne, and N. Bensiali, “On the stability of full
adaptive observer for induction motor in regenerating mode,”
IEEE Trans. Ind. Electron., vol. 57, no. 5, pp. 1599–1608,
May 2010.
[22] A. V. Ravi Teja and C. Chakraborty, “A novel model
reference adaptive controller for estimation of speed and stator
resistance for vector controlled induction motor drives,” in
Proc. IEEE ISIE, Bari, Italy, 2010, pp. 1187–1192.
R.S.Mandloi has obtained his B.E from Shri
Govindram Seksaria Institute of Technology and
Science (SGSITS), Indore, in 2003. He has obtained
his M.E from Shri Govindram Seksaria Institute of
Technology and Science (SGSITS), Indore, in 2006.
He has 6 years experience. He is presently working as
an Assistant Professor in SGSITS Indore. He is
working in the area of Power electronics, Drives and power quality.
Sourabh Jain has obtained his B.E from Samrat ashok
technology institute vidisha in the year 2008. He has
obtained his M.E from Shri Govindram Seksaria
Institute of Technology and Science (SGSITS), Indore,
in 2012. He has 2 years experience. He is working in the
area of Power electronics, Electric drives and power
quality.
Dr. Shailendra Sharma was born in Indore, India, in
1972. He received the M.E. degree in electrical
engineering with specialization in electronics from the
Shri Govindram Seksaria Institute of Technology and
Science (SGSITS), Indore, in 2004. He got Ph.D.
degree in the Department of Electrical Engineering,
Indian Institute of Technology (IIT) Delhi, New
Delhi.
He has five years of industrial experience as an
Erection and Commissioning Engineer with M/s Dhar Textile Mills Ltd.,
Indore. In 2004, he joined the Department of Electrical Engineering,
SGSITS, as an Assistant Professor. His fields of interest include power
electronics, electric drives, power quality, and renewable energy systems.
Mr. Sharma is an Associate Member of the Institution of Engineers, India.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Jil sutaria, Manisha shah and Chirag chauhan
41
Comparative Analysis of Single Phase and
Multiphase Bi-Directional DC-DC Converter
Jil sutaria, Manisha shah and Chirag chauhan
Abstract--A dc-dc converter has its applications, such as in
hybrid vehicles, solar inverters, in power supplies for
microprocessors etc. A bidirectional dc-dc converter can be
alternately operated as a step down converter in one direction of
energy flow and as step up converter in reverse direction of
energy flow, in places where both the sides have voltage sources.
A high voltage supply using a single converter is not preferred as
it leads to high ripple in output voltage and current, thus
requiring large value of inductor and filter capacitor. To
overcome these limitations multiphase interleaving technique is
used in bidirectional dc-dc converters i.e. connecting the
converters in parallel with the switching instants equally
distributed among them. This paper presents a comparative
study of the single phase and multiphase bi-directional dc-dc
converter and the optimization of inductor and filter capacitor.
The open loop simulation is done using simulink tool and
conclusions are drawn.
Keywords: Bi-directional, Interleaved, Multiphase, Ripple.
I. INTRODUCTION
The bidirectional DC-DC converters with energy storage
device have become very useful these days in various
applications where power flow is required to and from the
energy storage devices. The various applications are listed
below.
 Hybrid electric vehicles(HEV)
 Fuel cell energy systems
 Renewable energy storage systems
 Un-interruptible power supplies(UPS)
 Battery chargers
 Microprocessor applications
The DC-DC converters are designed in such a way that
they regulate the output voltage against the changes in the
input voltage and load current. It not only reduces the cost but
improves the efficiency of the system.
The converters can be broadly classified into isolated and
non-isolated converters depending on whether isolation is
provided between source and load. Based on this the
converters are reviewed in [1] and was concluded that the
isolated converters mainly used in renewable energy
applications , HEVs and more whereas the Non-isolated are
used in supply to microprocessors, UPS etc.
The isolated converters are commonly used for high voltage
application such as battery charging, as they provide galvanic
isolation between load and source [2]. The presence of
transformer in them leads to increase in their size, cost and
losses. The non-isolated bidirectional dc-dc converter
(NBDC) is therefore preferred in those systems where high
power density and high efficiency is required.
NBDC employing three inductors and four switches for
reducing current stress on switch and to get zero voltage
transition is used for HEV, but the control of the converter
here becomes complex [3].
Two n-level diode-clamped converter legs connected
back-to-back form an n-level converter. This topology is used
where both the sides of converter need to have same
grounding. The main feature of this topology is use of lower
voltage rating devices due to requirement of lower blocking
voltages. Two level and five level converters are proposed in
[4] and [5]. The current unbalance in capacitors is the main
limitation of the n-level topology.
The half bridge NBDC topology is used in [6], for energy
storage during regenerative breaking of DC motor. The half
bridge topology used here has less number of switches and is
easy to control.
This paper explores the possibility of using half bridge
NBDC connected in parallel for high voltage application,
thereby eliminating the use of transformer, making it compact
and achieving high power density and high efficiency.
Two bidirectional converters connected in parallel, with
same input and output are used. The study of single phase and
two phase bi-directional dc-dc converter is made and the
values of inductor and filter capacitor are optimised.
II. DIFFERENT TOPOLOGIES USED IN NON-ISOLATED
CONVERTERS
The NBDC topologies have been proposed in many ways
some with two switches and diodes for implementing ZVS and
ZCS, some having four switches .The four-switch NBDC is
shown in fig. 1. The left to right power transfer mode, Q1 and
Q4 act as active switches, while in the right to left power
transfer the opposite switches (Q2 and Q3) are controlled [7].
Jil sutaria is a Student, M Tech, Power electronics, machines and drives,
Nirma University, Manisha shah is working as Professor, Electrical
department, Nirma University and Chirag chauhan working in R&D head,
Suvik electronics Pvt Ltd, Email: 11meep15@nirmauni.ac.in
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Jil sutaria, Manisha shah and Chirag chauhan
42
Fig. 3. Single phase half bridge bi-directional dc-dc converter.
Fig. 1. Four switch NBDC.
The limitation here is that four switches are used, so
switching losses increases. For reducing the size of the
inductor and filter capacitor multiphase interleaving is used.
The fig. 2 shows multi device interleaved Boost converter with
two phase [13]. The switch S1 and S3 are connected to
inductor L1 are operated at 0 degree and 180 degree
respectively. The switch S2 and S4 are connected to L2 are
operated at 90 degree and 270 degree respectively.
The two phase topology shown in Fig. 4 along with
interleaving switching scheme forms two phase interleaving
converter. In the interleaving scheme [9] the PWM signals are
separated in phase over a switching period in 2∏/N radians,
being N the number of cells in parallel. The gating signals are
generated by comparing ramp signal with constant, which is
the duty cycle. As the individual input current of each
converter is displaced from the others, the net effect is that the
input and output current exhibits a switching frequency equal
to N* fs with reduced current ripple. Thus the size of input and
output capacitor reduces.
Fig. 4. Two phase half bridge topology.
Fig. 2. Multidevice Boost converter.
The main drawback here is that the number of switches
used per phase increases, thus increasing the switching losses,
and also the duty cycle of the switches should be maintained
equal, as any changes in it will lead to unequal current sharing
per phase, leading to high output current ripple.
III. CIRCUIT DESCRIPTION AND OPERATION
A. Chosen topology
The Non-isolated half bridge converter topology
consisting of two switches with anti-parallel diode connected
across them is shown in Fig. 3. The switch and anti-parallel
diode gives it the bidirectional nature. It is essentially a two
quadrant chopper, where the output voltage always remains
positive but the current becomes positive or negative
depending on the direction of power flow [8].
B. Circuit description
The multiphase converter is represented by a general purpose
model shown in fig. 2 [5]. There are two dc sources including
high side bus voltage source
and low side battery source
representing both voltage sources of the bidirectional
dc-dc converter. With two voltage sources, the averaged
inductor current or averaged output current Io can flow in
both directions.
Resistor
represents either high side source internal
resistance in buck mode or load in boost resistive load
application. Resistor
represents either low-side source
internal resistance in Boost mode or load in buck resistive load
application. Capacitor
and
indicate the bus
capacitor bank and the output capacitor at battery side
respectively.
C. Circuit operation
The working of the circuit is in two modes:
 Boost mode
 Buck mode
To make the converter work in continuous conduction mode
the duty cycle for Boost and Buck mode should be maintained
such that D1 + D2 = 1, where D1 is duty cycle in boost mode
and D2 is the duty cycle for Buck mode. The two phases work
180 degree phase shifted in one switching cycle, thus the
charging and discharging time of each inductor is reduced to
half .During Boost mode,
acts as a source with switching
period T. The lower switch S1 gets the gating signal and the
switch turns on, current flows through inductor L1, charging it
for a period of D1*(T/2). The charged inductor and the Source
get connected to the load
through the upper diode D3
for a period of (1-D1)*(T/2), giving high output. The other
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Jil sutaria, Manisha shah and Chirag chauhan
43
switch S2 turns on after 180 degree from the switch S1,
charging the inductor L2 for D1*(T/2). The inductor and the
source get connected to the load for a period of (1-D1)*(T/2).
Both the inductors share equal amount of current.
During the Buck mode
acts as source, and the
switches S3 and S4 conduct for a period D2*(T/2), and
freewheeling is done through diodes D1 and D2 for a period
(1-D2)*(T/2).
IV. DESIGN CALCULATION
The DC-DC converters can be classified as Buck
bi-directional and Boost bi-directional depending on where
the energy storing element is placed. The design equation of
both Buck and Boost converter are valid in designing this
converter. In this paper the converter is designed as Boost
converter.
The specifications of the converter are given below:
TABLE I SPECIFICATIONS OF DC-DC CONVERTER
When 7.2 mH is used the input ripple current exceeds the
allowed value of ripple current in single phase, so a larger
inductor could be used to limit it or higher ripple can be
allowed.
For two phase the same equation is valid but the value of
is reduced by N as two inductors charge in the same switching
cycle.
The current is divided among each phase so the overall ripple
current allowed from each inductor can be increased.
The value of inductor is thus halved i.e. 3.6 mH, but doing so
Input ripple current exceeds the Δ .
The effect of reduced ripple is seen only at the input and
output, the ripple through individual inductor comes to be
higher. Therefore the same value of inductor i.e. 7.2 mH is
used in single phase and two phase converter.
B. Capacitor calculation
The value of allowed output voltage ripple is 1 %.Thus the
voltage ripple is equal to,
ΔV =
= 4.5 V
(4)
In a multiphase converter the frequency as seen by the input
and output capacitor is N *fs, since the two converters are
connected in parallel and are operated 180 degree out of
phase. The ripple frequency thus increases leading to
reduction in size of capacitor. The value of capacitor can be
calculated as follows:
The maximum battery voltage can is 120 V. Therefore
= 120 V
As the battery can be allowed to discharge till 60 % the
minimum input voltage comes out to be:
=
= 72 V
(1)
The Value the input current and the output current calculated
are 8.33 A and 2.22 A respectively.
A. Inductor calculation
The calculation of inductor depends on the minimum input
voltage, inductor charging time and allowed ripple current.
Now for single phase, the value of the inductor can be
calculated as given below:
= 7.2mH
L=
(2)
Where, the time taken to charge the inductor
=
= 42
s
,
C=
= 8.88 µf
(5)
The used value capacitor used in two phase converter is 9 µf,
whereas in single phase converter it is 18 µf.
V. SIMULATION RESULTS
loop simulation is done for both Buck and Boost mode of
operation in continuous conduction mode of the converter.
The specifications considered for simulation are given in
Table I and the value of passive components used are as
calculated in design parameters. Fig. 4 shows the generalized
model used for simulation.
The results for single phase and two phase are shown and
compared. Resistive load of 202.5 Ω is used when operated in
Boost mode and 14.4 Ω is used in Buck mode.
A. Boost mode
The resulting Output voltage, Input current for single phase
and two phase are shown below.
(3)
The allowed input ripple current Δ
Δ
= 8.33 0.05 = 0.4166 A
depends on the maximum output voltage and minimum
input voltage.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Fig. 5(a). Output voltage: single phase converter.
Vol. 2, Issue. 1, April-2013.
Jil sutaria, Manisha shah and Chirag chauhan
44
[X-axis: 1 div = 0.001 Sec Y-axis: 1 div =1 V]
The value of output current remains same in both single phase
and two phase but the ripple in output current is much less in
case of two phase than in single phase. The value of ripple
content is tabulated in table 2.
Fig. 5(b). Output voltage: Two phase converter.
[X-axis: 1 div = 0.001 Sec Y-axis: 1 unit =1 V]
Fig. 8(a). Inductor current: one phase.
[X-axis: 1 div = 0.001 Sec Y-axis: 1 div = 0.1 A]
Fig. 6(a). Input current: single phase.
[X-axis: 1 div = 0.001 Sec Y-axis: 1 div = 0.2 A]
Fig. 8(b). Inductor current: two phase.
[X-axis: 1 div = 0.001 Sec Y-axis: 1 div = 0.1 A]
Fig. 6(b). Input current: two phase.
[X-axis: 1 div = 0.001 Sec Y-axis: 1 div = 0.2 A]
It can be observed from Fig. 5(b), Fig. 6(b) that the ripple
frequency at the output and input is twice then that in single
phase. The peak to peak (pk-pk) ripple in output voltage and
input current is lower in two phase. The ripple in output
voltage is 33.3% less in two phase as compared to single
phase. The input current ripple in single phase is 75% higher
than that in two phase.
As observed from Fig. 8(b), the inductor current in two phase
is shared equally among the two inductors, thus the ripple
current allowed in both the inductors can be increased. Also it
is noticeable that current through one inductor rises while the
other falls, thus cancelling out the ripple, resulting in ripple
reduction in output current.
B. Buck mode
Similar results were observed in Buck mode.
Fig. 9. Output voltage: two phase converter.
[X-axis: 1 div = 0.5 Sec Y-axis: 1 div =20 V]
Fig. 7(a). Output current: one phase.
[X-axis: 1 div = 0.001 Sec Y-axis: 1 div = 0.005 A]
Fig. 10. Output current: two phase converter.
[X-axis: 1 div = 0.5 Sec Y-axis: 1 div =2 A]
Fig. 7(b). Output current: two phase.
[X-axis: 1 div = 0.001 Sec Y-axis: 1 div = 0.005 A]
Fig. 9 and Fig. 10 show the output voltage and output current
in Buck mode for two phase. The value of output voltage is
positive 120 V, whereas the value of current is negative 8.33 A
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Jil sutaria, Manisha shah and Chirag chauhan
45
proving bi-directional power flow. Also the value of ripple in
output current is 0.3 % of the allowed ripple.
VI. COMPRISION OF SINGLE AND TWO PHASE
BI-DIRECTIONAL CONVERTER
The comparison of peak to peak ripple in single phase and two
phase output voltage, input and output current ripple is
tabulated below.
TABLE II COMPARISION OF RIPPLE CONTENT IN SINGLE PHASE
AND TWO PHASE CONVERTER
Fig. 11(a). Input current: single phase.
[X-axis: 1 div = 0.0005 Sec Y-axis: 1 div =2 A]
Fig. 11(b). Input current: two phase.
[X-axis: 1 div = 0.0005 Sec Y-axis: 1 div =2 A]
It can be observed from Fig. 11(a) that the input current shows
the rising slope for a time when inductor charges and becomes
zero during freewheeling time. The value of input current is
double in single phase than that in two phase as shown in Fig.
11(b).
From Table II it can be concluded that the ripple content
obtained in two phase converter is well within the range of
allowed ripple content. The value of input current ripple in
single phase Boost mode is 0.6Apk-pk whereas in two phase it
is 0.4Apk-pk, which is allowed. Thus in single phase the value
of inductor is to be increased to almost double of the value
used in two phase to bring back the ripple in allowable range.
The value capacitor decreases to half the value in single phase,
due to the use of multiphase interleaving. Thus the value of
passive components is optimized, making the converter
compact.
VII. CONCLUSION
Fig. 12(a). Inductor current: single phase.
[X-axis: 1 div = 0.0005 Sec Y-axis: 1 div = 0.1 A]
Fig. 12(b). Inductor currents: two phase.
[X-axis: 1 div = 0.0005 Sec Y axis: 1 div = 0.1 A]
Fig. 12(a) and Fig. 12(b) show the single phase and two phase
inductor currents.
It is observed from Fig. 12(a) that as only one inductor charges
and discharges in a cycle, so the charging time taken by it is
more, so its value is higher. As seen in Fig. 12(b) two inductors
are used, so the current as well as time of operation is shared
among them, thereby reducing the values.
In this paper the open loop simulation of single phase and
two phase half bridge bidirectional DC-DC converter is done
using Simulink tool on resistive load. The converter can be
used in applications where one side source is battery and other
side source is constant DC link voltage like in UPS or HEV.
The converter acts in buck mode while charging the battery
and acts in Boost mode while discharging the battery. It was
observed that by using the two phase topology with
interleaving switching technique the ripple frequency seen at
the input and output is twice as compared to single phase thus
leading to reduced ripple in both the working modes. As the
switching frequency seen is twice the actual switching
frequency, the value of capacitor reduces to half along with
reduction in switching losses. This increases the efficiency and
power density of the two phase converter. The overall thermal
losses of the two phase converter are limited due to division of
the power between the two phases.
REFERENCES
[1] K.C.Ramya, V.Jegathesan,”Review of Bi-Directional DC-DC
Converters Suited For Various Applications”, International
Journal of Research and Reviews in Electrical and Computer
Engineering (IJRRECE) ,Vol. 2, No. 2, June 2012
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Jil sutaria, Manisha shah and Chirag chauhan
46
[2] T.-F. Wu, Y.-C. Chen, J.-G. Yang, Y.-C. Huang, S.-S. Shyu* and
C.-L .Lee*, "1.5 kW Isolated Bi-directional DC-DC Converter
with a Flyback Snubber", PEDS 2009,pp.164-169,2-5 Nov
2009.
[3] M. Ahmadi, Student Member, IEEE, K. Shenai, Fellow, IEEE,
“New, Efficient, Low-Stress Buck/Boost Bidirectional DC-DC
Converter”, Energytech 2012,pp 1-6
[4] Petar J. Grbovi´c, Senior Member, IEEE, Philippe
Delarue,Philippe LeMoigne, Member, IEEE, and Patrick
Bartholomeus, “A Bidirectional Three-Level DC–DC Converter
for the Ultra capacitor Applications”,IEEE transactions on
industrial electronics, Vol. 57, N0. 10, October 2010
[5] Sergio
Busquets-Monge,
Salvador
Alepuz,
Josep
Bordonau,member IEEE,” A Novel Bidirectional Multilevel
Boost-Buck Dc-Dc Converter.” Energy conversion congress and
exposition.2009.
[6]
Premananda Pany1*, R.K. Singh2, R.K. Tripathi2,
“Bidirectional DC-DC converter fed drive for electric vehicle
system”, International Journal of Engineering, Science and
Technology, Vol. 3, No.3, 2011, pp.101-110
[7] S. Waffler and J. Biela and J.W. Kolar ,”Output Ripple
Reduction of an Automotive Multi-Phase Bi-Directional DC-DC
Converter”, IEEE 2009
[8] Ned Mohan,Tore. M. Undeland “Converters applications and
design”,Wiley publication, 2011.
[9] Kevin Thomas Delrosso ,”Analysis and Design of interleaving
multiphase DC- DC converter with LC _lter" , A thesis resented
to Faculty of California Poly- technic state University.
[10] Junhong Zhang , “Bidirectional DC-DC Power Converter
Design Optimization, Modeling and Control”, Dissertation
submitted to the Faculty of the Virginia Polytechnic Institute.
[11] Dr Miroslav Lazi1, Dr Milo ivanov2 and Boris ai Iritel.AD
Beograd,FTN Novi Sad,Spellman New York ,Serbia USA,
Desing of Multiphase Boost Converter for Hybrid Fuel Cell or
Battery Power Sources.
[12] A. Garrigo´s*, J.M. Blanes, J.L. Liza´n, “Non-isolated
multiphase Boost converter for a fuel cell with battery backup
power System”, International journal of hydrogen energy,
volume 36, issue 10, 2011
[13] Omar Hegazy, Member, IEEE, Joeri Van Mierlo, Member,
IEEE, and Philippe Lataire, “Analysis, Modeling, and
Implementation of a Multidevice Interleaved DC/DC Converter
for Fue Cell Hybrid Electric Vehicles” IEEE transactions on
power electronics, Vol. 27, No. 11, November 2012
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Pankaj Warak
47
Mathematical Modelling of Inverted Pendulum
with Disturbance Input
Pankaj Warak
Abstract— The Inverted Pendulum is an inherently open loop &
closed loop unstable system with highly nonlinear dynamics.
This is a system which belongs to the class of under actuated
mechanical system having fewer control inputs than the degrees
of freedom. The Inverted Pendulum is a very common problem
and so being one of the most important classical problems, the
control of Inverted Pendulum has been research interest in the
field of control engineering. In this paper modelling of nonlinear
Inverted Pendulum-cart dynamic system with disturbance input
have been presented. The aim of this case study is to stabilize
the Inverted Pendulum such that the position of the cart system
on the track is controlled quickly and accurately so that the
Pendulum is always erected in its inverted position during such
movements. Then, a linearized model is obtained from the
nonlinear model about vertical equilibrium point.
Keywords— Inverted Pendulum, Nonlinear System, Disturbance
Input.
1
INRODUCTION
Just like the broom-stick, an Inverted Pendulum is an
inherently unstable system. Force must be properly applied
to keep the system intact. To achieve this proper control is
required. The Inverted Pendulum is a nonlinear time variant
open loop system. So the standard linear technique cannot
model the nonlinear dynamics of the system. This makes the
system more challenging for analysis. The dynamics of
actual non-linear system is more complicated. But this
system can be approximated as a linear system if the
operating syatem is small, i.e. the variation of the angle
from the norm.
2
MATHEMATICAL MODELLING
2.1 Equations Of Motion
The diagram of a motor driven cart mounted inverted
pendulum is shown in fig.4.1
If we remember ever trying to balance a broom-stick on
our index finger of the palm of our hand, we had to
constantly adjust the position of our hand to keep the object
upright. An Inverted Pendulum does basically the same
thing. But in case of an Inverted Pendulum the motion is
restricted to one dimension only, where as in case of broomstick the hand is free to move in any directions.
Inverted Pendulum is very good platform for control
engineers to verify and apply different logics in the field of
control theory. Most of the modern technologies use the
basic concept of Inverted Pendulum, such as attitude control
of space satellites and rockets, landing of aircrafts,
balancing of ship against tide, Seisometers which monitors
motion of the ground due to earthquake and nuclear
explosions etc.
An Inverted Pendulum has its mass above the pivoted
joint, which is mounted on a cart which can be moved
horizontally. The Pendulum is stable while hanging
downwards, but the Inverted Pendulum is inherently
unstable and need to be balanced. In this case system has
one input- the force applied to the cart, and one disturbance
input here wind effect is considered, and two outputs –
position of the cart and angle of the Pendulum, making it as
a MIMO system. There are mainly three ways of balancing
an Inverted Pendulum i.e. (i) by applyaing a torque at the
pivoted point. (ii) by moving the cart horizontally. (iii) by
oscillating the support rapidly up and down.
Pankaj Warak is a Student, M.E. Control Systems, K.K.W. COE.
&Research, Nashik, Email: pwarak@gmail.com.
Fig.2.1 Inverted Pendulum-Cart System
It is assumed here that pendulum rod is mass-less, and
hinge is frictionless. The cart mass and the ball point mass at
the upper end of the inverted pendulum are denoted as M and
m, respectively. There is an externally x-directed force on the
cart, u(t), and the gravity force acts on the point mass at all
times. The co-ordinate system is considered is shown in
fig.4.1, where the x(t) represents the cart position and ө(t) is
the tilt angle referenced to the vertically upward direction.
Consider the inverted pendulum model with state feedback
with an additional disturbance input due to wind effects. Let
Fw represents horizontal wind force on the pendulum point
mass. The free body diagram of cart system and pendulum is
shown in fig.4.2 mass and fig.4.3.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Pankaj Warak
U(t)
48
Fw
N
(l + ml2)Ӫ + mgl SinӨ = - mlẍ CosӨ
2.6
The system under consideration is a non-linear system.
For ease of modeling and simulation, we have to take a small
case approximation such that the system will be linear one.
Let’s take a linearization point wiil be Ө= П.
P
Say Ө = П + Ф,
x
ẋ
M
Where, Ф is the angle between the pendulum and vertical
upwarddirection. If you choose Ф~0 then CosӨ= -1,
SindӨ/(dt) 2 = 0.
Fig.2.2 Free Body Diagram Of Cart
So, after linearization equation (2.6) becomes,
..
..
( I  ml 2 )  ml  ml x
2.7
And equation (2.3) becomes,
..
..
(M  m) x  ml   u  Fw
2.8
2.2 Transfer Function
Pendulum
Where,
joint
The transfer function of a linear, time invariant,
differential equation system is defined as ratio of the Laplace
transform of the output to the Laplace transform of the input
under the assumption that all the initial conditions are zero.
Fig.2.3 Free Body Diagram Of
M = mass of the cart
m = mass of ball point
Fw = Force of wind
u = externally applied force
ө = tilt angle referenced to vertical
L = length of pendulum
P = vertical component of reaction at pivoted
N = horizontal component of reaction at pivoted
joint
Now, adding all the forces on the cart in horizontal
direction,
Mẍ+ N = u + Fw
2.1
Adding all the forces on the pendulum in horizontal force
.

mẍ +mlӪ CosӨ - ml SinӨ = N
Substituting equation (2.2) in equation (2.2)
( M+m)ẍ + mlӪ CosӨ - ml
.

2
SinӨ = Fw + u
2.2
2.3
The equation 2.3 is called as force balance equation.
Now, all the forces along the vertical direction of the
pendulum,
P SinӨ + N CosӨ – mg SinӨ = mlӪ + mẍ CosӨ
initial condition.
L(output )
L(input )
,
at
zero
The Laplace transform of equation (2.7) is given by
(l+ml2)Ф(S)S2 – mglФ(S) = -mlX(S)S2
2.9
The Laplace transform of equation of (4.8) is given by
(M+m)X(S)S2 – mlФ(S)S2 = U(S)
2.10
Solving equation (2.9) for X(S),

  I
X (S )   


 ml 2 

ml


g 


2
S 

S 
2.11
Substituting equation (2.11) in (2.10),
2.4
Considering sum of the moments about the center of
gravity of the pendulum,
-Pl SinӨ – Nl CosӨ = lӪ
TF  G(s) 
2.12
From the above equation
2.5
Now from equation (2.4) and (2.5),
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Pankaj Warak
49
(Fx CosӨ)l – (FySinӨ)l = (mgSinӨ)l + (Fw CosӨ)l
2.17
And the equation (4.17) torque balance equation.
2.13
The equation (4.17) can be modified as ,
Where,




q  M  m I  ml 2   ml 2 




In equation (4.13), it is clear that two pole and zero is at
origin. This leads to cancellation of two pole and zero. So
resulting equation will be,
ml
 (S )
q

U (S ) S 2  (M  m)mgl
q
2.14
Here in this case the angle from the vertical position Ф(S)
is taken as the output and applied force to the cart U(S) is
taken as the input function.
mẍ CosӨ + mlӪ= mg SinӨ + Fw CosӨ
2.18
Solve the torque balance equation (4.18) for mlӪ and put
this into force balance equation
(4.3), giving
mlӪ= mg SinӨ + Fw CosӨ - mẍ CosӨ
2.19
and equation (4.3) becomes,
.
[M+m-mCos2Ө]ẍ = u + ml SinӨ  2 – mg SinӨCosӨ + Fw
Sin2Ө
2.20
Now, solve the torque balance equation for ẍ and put this
into the force balance equation,
giving,
..
.. mgSin  FwCos  ml 
x
mCos
2.21
Again from equation (2.11),
And force balance equation become,
mlS 2
 (S ) 
X (S )
2
2
( I  ml )S  mgl
2.22
Multiplying both the sides of equation (2.22) CosӨ gives,
2.15
Now putting the value of Ф(S) in equation (4.12),
2.16
Hence the distance of the cart from the origin is treated as
the output function whereas the applied force on the cart is
still the input function.
A
2.3 State Space Representation
Now, with this basic knowledge choosing the state
variables of the above considered pendulum,
x1= x ;
x2= ẋ=ẋ2;
x3=Ф;
x4= Ǿ =ẋ3;
Now, the torque in the clockwise direction caused by the
horizontal wind disturbance is Fw CosӨ l, and this term is
added to the torque balance to give,
Equation (2.22) becomes
2.23
Now the state equation can be written as,
d
d
x
dt
dt
2.24
Where,
x 
 1
x 
 2 
x 
 3
x 
 4 
d
dt
   x 
 .   2
   f 
    1
 x  x 
 .   4
  f 
 x   2 
M
uCosx  ( M  m ) gSinx  ml ( Sinx Cosx ) x 2 
FwCosx
1
1
1
1 2
1
m
f 
1
2
mlCos x  ( M  m )l
1
2.25
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Pankaj Warak
A upright
50
0

 (M  m) g

Ml
 
0

mg
 
Ml

1
0
0
0
0
0
0
0
 0 
 1
 Ml
Bupright  
0 
 1 


 M 
0

0
1

0

2.26
If both the pendulum angle and the cart position x are of
interest, we have
y=Cx
 
1
  Cx  
 x 
0
y
0 0
0 1
 
.
0  
 
0  x 
.
 
 x
or
It has two zero eigenvalues and two real eigenvalues
with apposite signs. Therefore this equilibrium in original
nonlinear system is unstable.
From the Lyapunov first theorem, the stability of the
pendulums pendent position can not be concluded from the
Jacobian linearization because of presence of two zero
eigenvalues. However for this system, the stability can be
directly inferred based on physical intuition and the “δ-ε”
type of definition of stability.
The pendulums pendent position is stable in the sense of
Lyapunov, because for any given ε-ball around the position,
we can find some perturbation δ which is small enough such
that cart and the pendulum oscillate within the given ε-ball.
2.27
Equation (2.24) and (2.27) give a complete state space
representation of the nonlinear inverted pendulum with
disturbance input.
When the Jacobian matrices are evaluated at the
reference point x0=0 and u0=0, a linearized model can also be
developed as,

0
 (M  m)g

d

x   Ml
0
dt

mg

 
M

1 0 0
0 0
0 0
0 0
 0 
 0 

 1 
 1


0



 Ml


x  
u   ml Fw
1
 0 
0


 1 


0


0



 M 
2.28
This is open loop linearized model for the inverted
pendulum with a cart force δu(t), and a horizontal wind
disturbance δFw(t). The two inputs have been separated for
convenience, thus the LTI system can be written as
d
x  Ax  b u  b Fw
1
2
dt
4.29
3. CONCLUSION
The Jacobian linearized around the equilibrium can be
obtained by directly from the state space equations which
yields,
REFERENCES
[1] K. Ogata, Modern Control Engineering, 4th ed, Pearson
Education(Singapore) Pvt. Ltd., New Delhi, 2005, chapter 12.
[2] K. Ogata, System Dynamics, 4th ed, Pearson Education
(Singapore) Pvt.Ltd., New Delhi, 2004,
[3] J. R. White, System Dynamics: Introduction to the Design and
Simulation of Controlled Systems, the online literature available
at:
http://www.profjrwhite.com/system_dynamics/sdyn/s7/s7invpc3
/s7invp c3.html, and
http://www.profjrwhite.com/system_dynamics/sdyn/s7/s7invp1/s7in
vp1.html.
[4] Ajit K. Mandal, Introduction to Control Engineering, New Age
International Pub., New Delhi, 2000, Chapter 13.
[5] F. L. Lewis, Optimal Control, John Wiley & Sons Inc., New
York, 1986.
[6] M. N. Bandyopadhyay, Control Engineering: Theory and
Practice, Prentice Hall of India Pvt. Ltd., New Delhi, 2004,
Chapter 13.
[7] Roland S. Burns, Advanced Control Engineering, Elsevier –
Butterworth Heinemann, 2001, Chapters 9 & 10.
[8] Astrom K. J., and McAvoy Thomas J., “Intelligent control”, J.
Proc. Cont. 1992, Vol. 2, No 3, pp 115-127.
[9] T. I. Liu, E. J. Ko, and J. Lee, “Intelligent Control of Dynamic
Systems”, Journal of the Franklin Institute, Vol. 330, No. 3, pp.
491-503, 1993.
[10]Yasar Becerikli, Ahmet Ferit Konar, and Tarıq Samad,
“Intelligent optimal control with dynamic neural networks”,
Elsevier Journal of Neural Networks, Vol. 16, 2003, pp 251–
259.
[11]D. Murali, Dr. M. Rajaram , “Simulation and Implementation of
DVR for Voltage Sag Compensation , International Journal of
Computer Applications (0975 – 8887), Volume 23– No.5, June
2011 (9)

x
 Ax  Bu
where
3.1
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr.K.Saravanan and Dr. H. Habeebullah Sait
51
Multi Input Converter for Distributed
Renewable Energy Sources
Mr.K.Saravanan and Dr. H. Habeebullah Sait
ABSTRACT: In renewable energy sources, such as wind, solar
energy, the generated voltages often vary because of
environmental changes. A hybrid distribution system fed by
photovoltaic (PV) and fuel cell (FC) is proposed. It works to
feed the load without any interuption.PV is used as the
primary source of power operating near maximum power
point (MPP), with the FC section, acting as a current source,
feeding only the deflict power. The multi input converter
eliminates the use of a separate conventional DC/DC boost
converter stage required for PV power processing, resulting in
reduction of the number of devices, components and sensors.
The generated power is fed to the load and battery. In case of
power demand battery is used to compensate the load. The
other advantages of this system include low cost, compact
structure and high reliability. The analytical, simulation and
results of this research are presented.
Key Word: Hybrid Power System ( HPS),Solar cell
(PV),Maximum power point (MPP),Multi input converter
(MIC),Fuel cell (FC),lead acid battery and pulse width
modulation(PWM).
1. INTRODUCTION:
With increasing concern of global warming and the
depletion of fossil fuel reserves, many are looking at
sustainable energy solutions to preserve the earth for the
future generations. Other than hydro power, wind and
photovoltaic energy holds the most potential to meet our
energy demands. Wind energy alone is capable of supplying
large amounts of power but its presence is highly
unpredictable as it can be here one moment and gone in
another. Similarly, solar energy is present throughout the
day but the solar irradiation levels vary due to sun intensity
and unpredictable shadows cast by clouds, birds, trees, etc.
The common inherent drawback of wind and photovoltaic
systems are their intermittent natures that make them
unreliable. So, the number of applications which need more
than one power source is increasing. Fuel cell is used to
overcome this. Distributed generating systems or micro-grid
systems normally use more than one power source or more
than one kind of energy source. A parallel connection of
converters has been used to integrate more than one energy
source in a power system.
Mr.K.Saravanan is a PG Scholar, Power System Engineering and Dr. H.
Habeebullah Sait,Ph.D, is working as Assistant Professor/EEE, Anna
University :: Chennai, Regional Office Tiruchirappali (BIT Campus). Email
ID:saravanan23eee@gmail.com, habisait@gmail.com
2. NEED FOR MULTIPLE CONVERTER
SYSTEM:
In most power electronic systems, input power, output
demand, or both instantaneously change and are not exactly
identical with each other at any time instant. Hence,
providing a good match between them is a complicated task
to deal with if not impossible. Furthermore, due to the wide
variation of processed power, overall efficiency of the
system is not high. Hence, additional energy sources are
required to assist the main source in fulfilling the load
demand. Hence multi-input converter play an important role
due to power demand.
2.1 MULTI INPUT CONVERTERS (MIC):
Placing converters either in parallel or series results in
use of more number of components, more losses, and less
efficiency. Hence, use of a single multi-input converter is
preferred to using several multiple converters. One approach
of deriving multi-input converters is using the principle of
flux additivity . In this type of systems, energy sources are
combined in the magnetic form by adding up their produced
magnetic flux together in the magnetic core of the coupled
transformer instead of combining them in the electric form.
However,a multiple-input converter (MIC) can generally
have the following advantages compare to a combination of
several individual converters. They are cost reduction,
compactness, more expandability and greater manageability.
First, this study suggests MIC topology comparison criteria
that can be used as a decision guide for choosing a MIC
topology depending on the application. The above said
converters gives a brief introduction about their topologies,
connections and consideration for using multi-input
converters.
3.1 SOLAR:
3. RENEWABLE ENERGY:
Solar power is the conversion of sunlight into electricity,
either directly using photovoltaic (PV), or indirectly using
concentrated solar power (CSP .Photovoltaic convert light
into electric current using the photoelectric effect.
Photovoltaic were initially used to power small and
medium-sized applications, from the calculator powered by
a single solar cell to off-grid homes powered by a
photovoltaic array. Solar cells produce direct current (DC)
power, which fluctuates with the intensity of the irradiated
light. This usually requires conversion to certain desired
voltages or alternating current (AC), which requires the use
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr.K.Saravanan and Dr. H. Habeebullah Sait
52
of inverters. Multiple solar cells are connected inside the
modules. Modules are wired together to form arrays, then
tied to an inverter, which produces power at the desired
voltage, and for AC, frequency/phase. Renewable energy
sources are gaining more interest in recent years. Among
them, photovoltaic (PV) panels, that offer several
advantages such as requirement of little maintenance, no
environmental pollution. Recently, PV arrays are used in
many applications such as battery chargers, solar powered
water pumping systems, grid connected PV systems, solar
hybrid vehicles, and satellite power systems.
Irs(T)=Irsr(T/Tr)exp[(S/m)((1/Vtr)-(1/Vt)
(3)
3.1.1 Photovoltaic Characteristic:
Solar cells have a nonlinear I/V characteristic which is
dependent on the level of solar irradiation and the cell
temperature. A solar cell can be accurately modeled by a
current source in parallel with a diode, as illustrated in Fig.
RP and RS are the shunt and series resistances representing
the losses in the photovoltaic conversion process and
connections to the cell respectively.
Figure. 2. Characteristics of PV
The output power of a PV cell is indeed a non linear
function of the operating voltage and this function has a
maximum power point (MPP) corresponding to a particular
value of voltage. In order to operate at the MPP, an energy
power converter must be connected at the output of a PV
array, such converter forces the output voltage of the PV
array is equal to the optimal value, also taking into account
the atmospheric condition.
3.1.2 MAXIMUM POWER POINT TRACKING ON
PV:
Figure. 1. Single PV Cell
I(S,T,V)=Iph(S)-Irs(T) [exp(V+(RS1/mvt) -1)]
(1)
Using the model of Figure 3. 1, the output current of a
solar cell can be described in terms of the solar irradiation,
cell temperature and voltage. Where S is the level of solar
irradiation in W/m2, T is the solar cell temperature in
Kelvin, V is the voltage across the cell in Volts and m is the
dimensionless P/N junction ideality factor of the diode in
the model. VT (T) is the thermal voltage for a given
temperature in Kelvin, given by VT(T)=kT/q where k is the
Boltzmann constant (1.39x10- 23J/K) and q is the electron
charge (1.6x10-19C). RS and RP are the series and shunt
resistances in Ohms. The photocurrent IPH, generated by
the photovoltaic conversion process, can be expressed in
terms of the solar irradiation S, a reference level of solar
irradiation Sr and the photocurrent in Amps at the reference
irradiation level.
Ipm(S)=Iphr(S/Sr)
(2)
The reverse saturation current IRS is a loss in the
conversion process due to a reverse current which flows
through the diode, dependent on temperature. It can be
expressed in terms of the cell temperature T (K), a reference
temperature Tr (K), the reverse saturation current at the
reference temperature Irsr (A), the band gap energy of the
semiconductor used to manufacture the cell ε (1.12eV for
silicon), the diode ideality factor, m, and VT and VTR
which are the thermal voltages at T and TR respectively in
volts.
The maximum power point tracking (MPPT) is usually
an essential part of a photovoltaic power generation system,
because of nonlinear characteristics of photovoltaic array.
As such, many MPPT methods have been developed and
implemented. When the entire array does not receive
uniform solar irradiance (i.e. partial shading condition), the
multiple local maxima appear on P-V characteristic curve of
PV array. Inspite of conventional popular MPPT methods
(i.e. P&O, IncCond, RCC, Two-mode etc.) are effective
under uniform solar irradiance, the presence of multiple
local maxima reduces the effectiveness of the conventional
MPPT methods
3.1.3 INCREMENTAL CONDUCTANCE:
The incremental conductance method is based on the
fact that the slope of the PV array power curve is zero at the
MPP, positive on the left of the MPP, and negative on the
right, as given by
dP/dV=0, at MPP
(4)
dP/dV>0,left of MPP
(5)
dP/dV<0,right of MPP
(6)
Since
dP/dV=d(IV)/dV= I + V(dI/dV) =I+V(ΔI/ΔV)
(7)
( can be rewritten as)
ΔI/ΔV=−I/V, at MPP
(8)
ΔI/ΔV>− I/V, left of MPP
(9
ΔI/ΔV<−I/V, right of MPP.
(10)
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
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Mr.K.Saravanan and Dr. H. Habeebullah Sait
The MPP can thus be tracked by comparing the
instantaneous conductance (I/V ) to the incremental
conductance (ΔI/ΔV ). Vref is the reference voltage at which
the PV array is forced to operate. At the MPP, Vref equals
to VMPP. Once the MPP is reached, the operation of the PV
array is maintained at this point unless a change in ΔI is
noted, indicating a change in atmospheric conditions and the
MPP. The algorithm decrements or increments Vref to track
the new MPP. The increment size determines how fast the
MPP is tracked. Fast tracking can be achieved with bigger
increments but the system might not operate exactly at the
MPP and oscillate about it instead; so there is a tradeoff. A
method is proposed that brings the operating point of the PV
array close to the MPP in a first stage and then uses IncCond
to exactly track the MPP in a second stage. By proper
control of the power converter, the initial operating point is
set to match a load resistance proportional to the ratio of the
open-circuit voltage (VOC) to the short-circuit current (ISC)
of the PV array. This two-stage alternative also ensures that
the real MPP is tracked in case of multiple local maxima. In
a linear function is used to divide the I–V plane into two
areas, one containing all the possible MPPs under changing
atmospheric conditions. The operating point is brought into
this area and then IncCond is used to reach the MPP. A less
obvious, but effective way of performing the IncCond
technique is to use the instantaneous conductance and the
incremental conductance to generate an error signal
e=I/V+dI/dV
(11)
A simple proportional integral (PI) control can then be
used to drive e to zero. Measurements of the instantaneous
PV array voltage and current require two sensors.
The most popular MPPT algorithms according to the
number of publications are P&O, InCond and Fuzzy Logic.
It makes sense because they are the simplest algorithms
capable of finding the real MPP. The performance of these
three algorithms is analyzed. They were selected because of
their simplicity and popularity. In the case of P&O and
InCond some modifications are proposed, which overcome
the limitations of the original methods in tracking the MPP
under irradiation slopes. The FLC is designed according to
the references and its dynamic efficiency is tested and
compared to the hill-climbing MPPT methods.
3.2 FUEL CELL OPERATION
The fuel cell is an electrochemical devise, which
converts chemical energy of the fuel to electricity by
combining gaseous hydrogen with air in the absence of
combustion. The basic principles of operation of the fuel
cell is similar to that of the electrolyser in that the fuel cell is
constructed with two electrodes with a conducted electrolyte
between them. The heart of the cell is the the proton
conducting solid Proton Exchange Membrane (PEM). It is
surrounded by two layers, a diffusion and a reaction layer.
Under constant supply of hydrogen and oxygen the
hydrogen diffuses through the anode and the diffusion layer
up to the platinum catalyst, the reaction layer. The reason
for the diffusion current is the tendency of hydrogen oxygen
reaction.Two main electrochemical reactions occur in the
fuel cell. One at the anode (anodic reaction) and one at the
cathode. At the anode, the reaction releases hydrogen ions
and electrons whose transport is crucial to energy
production.
53
H22H+ + 2e(12)
The hydrogen ion on its way to the cathode passes
through the polymer membrane while the only possible way
for the electrons is though an outer circuit. The hydrogen
ions together with the electrons of the outer electric circuit
and the oxygen which has diffused through the porous
cathode reacts to water.
2H+ + ½ O2 + 2e- H2O
(13)
The water resulting from this reaction is extracted from
the system by the excess air flow. The reaction is:
H + ½ O2 H2O
(14)
This process occurs in all types of fuel cells.
Figure .3. Fuel Cell
Figure .4. Voltage- Current Characteristics
Figure .5. Power- Current Characteristics
Figure .6 .Load Characteristics
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr.K.Saravanan and Dr. H. Habeebullah Sait
4. MULTI INPUT CONVERTER FOR SOLAR
CELL AND FUEL CELL
The general block diagram of the three-input dc–dc
boost converter is represented in Figure 7. As seen from the
Figure 7, the converter interfaces two input power sources
v1 and v2, and a battery as the storage element. This
converter is suitable for hybrid power systems of PV, FC,
and wind sources. Therefore, v1 and v2 are shown as two
dependent power sources that their output characteristics are
determined by the type of input power sources. For
example, for a FC source at the first port, v1 is identified as
a function of its current iL1. The PV source at the second
port, v2 is identified as a function of its current iL2 depends
upon light intensity, and ambient temperature. In the
converter structure, two inductors L1 and L2 make the input
power ports as two current sources, which result in drawing
smooth dc currents from the input power sources. Figure 8,
represents the equivalent design circuit of the proposed
system.
54
The converter structure shows that when switches S3 and
S4 are turned ON, their corresponding diodesD3 andD4 are
reversely biased by the battery voltage and then blocked. On
the other hand, turn-OFF state of these switches makes
diodes D3 and D4 able to conduct input currents iL 1 and iL
2. In hybrid power system applications, the input power
sources should be exploited in continuous current mode
(CCM). For example, in the PV or FC systems, an important
goal is to reach an acceptable current ripple in order to set
their output power on desired value. Therefore, the current
ripple of the input sources should be minimized to make an
exact power balance among the input powers and the load.
Therefore, in this paper, steady state and dynamic behavior
of the converter have been investigated in CCM In general,
depending on utilization state of the battery, three power
operation modes are defined to the proposed converter.
These modes of operation are investigated with the
assumptions of utilizing the same saw tooth carrier
waveform for all the switches, and d3, d4 <min (d1,d2 ) in
battery charge or discharge mode. Although exceeding duty
ratios d3 and d4 from d1 or d2 does not cause converter
malfunction, it results in setting the battery power on the
possible maximum values. In order to simplify the
investigations, it is assumed that duty ratio d1 is less than
duty ratio d2. Further, with the assumption of ideal switches,
the steady-state equations are obtained in each operation
mode.
4.1
FIRST
POWER
OPERATION
MODE
(SUPPLYING THE LOAD WITH SOURCES V1 AND
V2 WITHOUT BATTERY EXISTENCE)
Figure .7. General block Diagram
The RL is the load resistance, which can represent the
equivalent power feeding an inverter. Four power switches
S1 , S2 , S3 , and S4 in the converter structure are the main
controllable elements that control the power flow of the
hybrid power system. The circuit topology enables the
switches to be independently controlled through four
independent duty ratios d1 , d2 , d3 , and d4, respectively.
As like as the conventional boost converters, diodes D1 and
D2 conduct in complementary manner with switches S1 and
S2.
Figure .8. Circuit Topology Of The System
In this operation mode, two input power sources v1 and
v2 are responsible for supplying the load, and battery
charging/ discharging is not done. This operation mode is
considered as the basic operation mode of the converter. As
clearly seen from the converter structure, there are two
options to conduct input power sources currents iL 1 and iL
2 without passing through the battery; path 1: S4–D3 , path
2: S3–D4.
Figure.9. Steady-State Waveform Of The Converter In
(a) First Operation Mode, (b) Second Operation Mode And
(c) Third Operation Mode
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr.K.Saravanan and Dr. H. Habeebullah Sait
Switching state 1 (0 < t < d1 T): At t = 0, switches S1
and S2 are turned ON and inductors L1 and L2 are charged
with voltages across v1 and v2.
Switching state 2 (d1 T < t < d2 T): At t = d1T, switch
S1 is turned OFF, while switch S2 is still ON (according to
the assumption d1 < d2). Therefore, inductor L1 is
discharged with voltage across v1 − vo into the output load
and the capacitor through diode D1, while inductor L2 is
still charged by voltage across v2.
Switching state 3 (d2T < t < T): At t = d2T, switch S2
is also turned OFF and inductor L2 is discharged with
voltage across v2 − vo, as like as inductor L1. In this
operation mode, the control strategy is based on regulating
one of the input sources on its reference power with its
corresponding duty ratio, while the other power source is
utilized to regulate the output voltage by means of its duty
ratio.
4.2
SECOND
POWER
OPERATION
MODE
(SUPPLYING THE LOAD WITH SOURCES V1, V2
AND BATTERY CHARGING PERFORMANCE)
55
Therefore, inductors L1 and L2 are charged with voltages
across v1 and v2.
Switching state 3 (d1T < t < d2T): At t = d1T, switch
S1 is turned OFF, so inductor L1 is discharged with voltage
across v1− v0 , while inductor L2 is still charged with
voltages across v2.
Switching state 4 (d2T < t < T): At t = d2T, switch S2
is also turned OFF and inductors L1 and L2 are discharged
with voltage across v1 – v0 and v2 – v0. By applying
voltage–second and current–second balance theory to the
converter, following equations are obtained. In this
operation mode, the control strategy is based on regulating
both of the input power sources on their reference powers by
means of their corresponding duty ratios d1 and d2, while
the battery discharge power is utilized to regulate the output
voltage by duty ratio d4.
Switching state 1 (0 < t < d3 T): At t = 0, switches S1 ,
S2 , and S3 are turned ON, so inductors L1 and L2 are
charged with voltages across v1 and v2 , respectively .
Switching state 2 (d3 T < t < d1 T): At t = d3 T, switch
S3 is turned OFF while switches S1 and S2 are still ON
(according to the assumption). Therefore, inductors L1 and
L2 are charged with voltages across v1 − vB and v2 − vB
respectively.
Switching state 3 (d1 T < t < d2 T): At t = d1 T, switch
S1 is turned OFF, so inductor L1 is discharged with voltage
across v1− v0, while inductor L2 is still charged with
voltage across v2− vB.
Switching state 4 (d2 T < t < T): At t = d2 T, switch S2
is also turned OFF and inductor L2 as like as L1 is
discharged with voltage across v2 – v0.
In this operation mode, if the total generated power of
the input sources becomes more than the load power, the
battery charging performance will be possible if duty ratio
d3 is utilized to regulate the output voltage. With this
control strategy, duty ratios d1 and d2 are
utilized to regulate powers of the input sources, while
duty ratio d3 is utilized to regulate the output voltage
through charging the battery by the extra-generated power.
4.3 THIRD POWER OPERATION MODE
(SUPPLYING THE LOAD WITH SOURCES V1 AND
V2 AND THE BATTERY)
Switching state 1 (0 < t < d4T): At t = 0, switches S1 ,
S2 , and S4 are turned ON, so inductors L1 and L2 are
charged with voltages across v1 + vB and v2 + vB .
Figure 10 Simulation Diagram
Switching state 2 (d4T < t < d1T): At t = d4T, switch
S4 is turned OFF, while switches S1 and S2 are still ON.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
5.SIMULATION
Vol. 2, Issue. 1, April-2013.
Mr.K.Saravanan and Dr. H. Habeebullah Sait
56
In this stage, the requirement of load power PL is 100W
while the maximum available PVpower is 140W and the
maximum available FC power is 150W.The sun irradiation
level is G = 750W/m2. There is no need to charge the
battery. First, second, third and fourth duty ratios are set as
d1=0.7,d2=0.75,d3=0 and d4=1. By setting d3 = 0 and d4 =
1, which result the battery power to be set on zero value.
The FC current is regulated by d1,which shows iL1 =0.85A.
The PVcurrent is regulated by d2, which shows iL2 =0.45A.
The results are shown in the Figure 11,12,13.The required
load voltage is maintained for its entire operating time.
In this stage, the sun irradiation level increase to G
=1000W/m2, while the load power remains constant at PL =
100W. In addition, in this stage, the battery charging is
assumed to be performed, so the third operation mode is
chosen for the converter. In this condition, battery remains
in charging due to increase in sun irradiation level. As
shown in Figure, the battery has been charged. The FC
current is regulated on iL1 = 8.85 to 0.9A with duty ratio d =
0.73, while the maximum power of the PV source is tracked
with regulating the PV current at iL2 =0.3A and adjusting
the first duty ratio at d1 = 0.79. Moreover, controlling the
third and fourth duty ratios at d3 = 0.45 and d4 = 0,
respectively, results in providing the charging power of the
battery in addition to regulating the output voltage Which
are shown in Figure 14,15,16.
Figure 11 Gate Pulse For Four Switches G1,G2,G3 And
G4 Vs time
Figure 14 Gate Pulse For Four Switches G1,G2,G3 And
G4 Vs Time
5.1 FIRST SIMULATION STAGE
Figure 12 Battery Output Voltage ,Current Value Vs
Time For First Operating Mode
Figure 13 Compasison Of Voltages Of Solarcell,
Fuelcell And Load Vs Time
5.2 SECOND SIMULATION STAGE
Figure 15 Battery Charging Voltage,Current, SOC Vs
Time For Mode Second Operating
Figure 16 Compasison Of Voltages Of Solarcell,
Fuelcell And Load Vs Time
5.3 THIRD SIMULATION STAGE
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr.K.Saravanan and Dr. H. Habeebullah Sait
57
This stage occurs in a condition that solar power
decreased certain value in which the load requires PL
=100W and the PV power is simultaneously decreased due
to sun irradiation level of G = 500 W/m2. From the
maximum deliverable power of the PV, it is obviously
understood that the PV is not able to completely supply the
power deficiency thus, the remained power should be
supplied by the battery. Therefore, the second operation
mode is chosen. The PV is accomplished by regulating its
current at iL2 =0.24A and adjusting the first duty ratio at d2
= 0.73, while the maximum power of the FC is delivered at
iL2 =1.25 A with adjusting the second duty ratio at d2 =
0.71. The controlling the third and fourth duty ratios at d3 =
1 and d4 = 0.4 results in discharging the battery which are
shown in Figure 17, 18.
Figure 18 Compasison Of Voltages Of Solar Cell,
Fuelcell And Load
Table 1 Simulation Results
CONCLUSION AND FUTURE WORK
Figure 17 Gate Pulse For Four Switches G1,G2,G3
And G4 Vs Time
MODE1
750W/m
MODE2
1000W/
m2
MODE3
500W/m2
Load current
0.6A
0.6A
0.78A
Load voltage
126.5V
126.5V
126.5V
Load power
75.9W
75.6W
98.6W
---
Chargin
g
Discharging
45V
50V
45V
0.78A
0.9A
1.35A
35W
45W
49.5W
13.9V
13.9V
13.2V
0.49A
0.49
0.24A
6.811W
6.811W
6.336W
40.86W
40.86W
38.016W
PARAMETE
R
Battery
voltage,curre
nt and SOC
Fuel
cell
voltage
Fuel
cell
current
Fuel
cell
power
Solar voltage
output
Solar current
output
Power output
from
solar
cell for 2 Cell
in Series
Power output
from
solar
cell for 12
cell
2
In this work, literature review for various types of
multiple input converter has been studied. Multi input boost
converter was designed for fuel cell and solar panel. Since
the cost of fuel cell is high and it depends upon hydrogen
source at any instant fuel is required. And cost of fuel cell is
high. So that is replaced by wind turbine in future. As per
the requirement load requires 100w power which is
continuously supplied by two sources. Alternatively battery
backup is supplied during power deficiency. Results show
that a photovoltaic fuel-cell hybrid system can perform well
to meet the external load using energy produced by the
system. It defines the downside of other types of hybrid
power resources. Thus the system has been designed,
optimized and control strategy has been considered for DC
load only. In order to supply AC load, which are more
frequently used, the system requires inverters to convert DC
power to AC. However, the choice of the components in any
case should rather be determined by economic
consideration. Thus, the addition of battery to the system
helps the fuel cell to handle the load where it draws the
power from the battery until the fuel cell supports the
increased of load demand. The battery provides additional
power for any period of time. The boost converter is
responsible for the energy conversion of the fuel cell and
converts the power to a higher voltage application.
REFERENCES
[1] Chen Y. M, Liu Y. Ch. and Wu F. Y.(2002) ‘Multi-input
DC/DC converter based on the multi winding transformer for
renewable energy applications’,IEEE Trans. Ind. Electron., vol.
38, no. 4, pp. 1096–1103.
[2] Chen Y. M, Liu Y. Ch, Hung S. C. and Cheng C. S.(2007)
‘Multi-input inverter for grid-connected hybrid PV/Wind
power system’,IEEE Transactions on Power Electronics, vol.
22, no. 3, pp. 1070–1077.
[3] Chuang Y. C. and Ke Y. L.(2008) ‘ High-efficiency and lowstress ZVT-PWM DC-to-DC converter for battery charger’,
IEEE Transactions on Power Electronics,vol. 55, no. 8, pp.
3030–3037.
[4] Duarte J. L, Hendrix M. and Simoes M. G.(2009) ‘Three-port
bidirectional converter for hybrid fuel cell systems’,IEEE
Transactions on Power Electronics ,vol. 22, no. 2, pp. 480–487.
[5] Farzam Nejabatkhah, Saeed
Danyali, Seyed
Hossein
Hosseini(2012) ‘Modeling and Control of a New Three-Input
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mr.K.Saravanan and Dr. H. Habeebullah Sait
[6]
[7]
[8]
[9]
[10]
58
DC–DC Boost Converter for Hybrid PV/FC/Battery Power
System’ , IEEE Transactions on Power Electronics, vol. 27,
no. 5
Gopinath R, Kim S, Hahn J. H, Enjeti P. N, Yeary M. B. and
Howze J. W.(2004) ‘Development of a low cost fuel cell
inverter system with DSP control’,IEEE Transactions on
Power Electronics,vol. 19, no. 5, pp. 1256–1262.
Huang X, Wang X, Nergaard T, Lai J. S, Xu X, and Zhu
L.(2004) ‘Parasitic ringing and design issues of digitally
controlled high power interleaved boost converters’,IEEE
Transactions on Power Electronics, vol. 19, no. 5, pp. 1341–
1352.
Jia J, Li Q, Wang Y, Cham Y. T. and Han M.(2009)
‘Modeling and dynamic characteristic simulation of a proton
exchange membrane fuel cell’, IEEE Transactions on Energy
Converservation vol. 24, no. 1, pp. 283–291.
Jiang W. and Fahimi B.(2010) ‘Active current sharing and
source management in fuel cell- battery hybrid power
system’,IEEE Transactions on Power Electronics.vol. 57, no. 2,
pp. 752–761.
Jin K, Ruan X, Yang M. and Xu M.(2009) ‘A hybrid fuel cell
power system’,IEEE Transactions on Power Electronics, vol.
56, no. 4, pp. 1212–1222.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Seelam Swarupa, and K. V. S. Ramachandra Murthy
59
Control Strategy for Unified Power Flow
Controller
Seelam Swarupa, and K. V. S. Ramachandra Murthy
Abstract:
In this thesis, a reactive power
coordination controller has been implemented to limit
excessive voltage excursions during reactive power
transfers. The controller implemented coordinates
Reactive Power flows. Response of Power System to Step
Changes in Reactive Power Flow Reference has been
examined in this Thesis. This Thesis reviews the
methodology given in [1] and extends beyond its scope.
The response of two bus system consisting of
UPFC is studied with and without coordination
controller. A two bus system is considered with 13.8 kV
generator of 1000 MVA and step up transformer of 13.8
kV/230 kV, 1000 MVA. The step change in the reference
reactive power of 50 MVAr to 225 MVAr has been
introduced in the system and Peak over shoot in the
reactive power oscillations have been observed with and
without coordination controller of UPFC. Similar
analysis is carried out on with 13.8kV/345 kV
Transformer. It is observed that there is an improvement
of 20% reduction in the peak overshoot of the reactive
power oscillations. The modeling and analysis have been
carried out in the MATLAB/SIMULINK environment.
Keywords : UPFC, Control Strategy, reactive power
control.
I. INTRODUCTION
Power system in general are interconnected for
economic, security and reliability reasons. Exchange of
contracted amounts of real power has been in vogue for a
long time for economic and security reasons. To control the
real flow on tie lines connecting controls areas, power flow
control equipment such as phase shifters are installed. They
direct real power between control areas. The interchange of
real power is usually done on hourly basis. On the other
hand, reactive power flow control on tie lines is also very
important. Reactive power flow control on transmission
lines connecting different areas is necessary to regulate
remote end voltages. Though local control actions within an
area are the most effective during contingencies, occasions
may arise when adjacent control areas may be called upon
to provide reactive power to avoid low voltages and improve
system security.
Fixed series capacitors help in increasing stability limits
in an interconnected power system. With transmission open
access, each transmission system owning utility will increase
their transmission capacity to attract more utilities to use its
transmission facilities. Many existing power systems have
already made the use of series compensation to increase their
transmission capacity . By series compensation, the amount
of reactive power consumed by the line is reduced hereby
increasing the amount of reactive power transferred to the
receiving end and improving the voltage profile at the
receiving end. This is one of the secondary benefits of using
series compensation. Under system disturbance conditions
like three phase faults or line tripping, controllable series
compensation helps in damping power system oscillations.
Excessive UPFC bus voltage excursions during reactive
power transfers requiring reactive power coordination have
been addressed in by Jayaram and Salama[1]. L. Gyugyi,
proposed [2] the unified power flow controller (UPFC)
which is able to control the reactive power flows at the
sending- and the receiving-end of the transmission line. K.
K Sen proposed [3] the theory and the modeling technique
of a flexible alternating current transmission systems
(FACTS) device, namely, unified power flow controller
(UPFC) using an Electromagnetic Transients Program
(EMTP) simulation package.
A collection of measured performance characteristics
are presented [4] to illustrate the unique capabilities of the
UPFC by Renz. P. K. Dash, proposed [5] the design of
radial basis function neural network controllers (RBFNN)
for UPFC to improve the transient stability performance of a
power system. P.K Dash proposed [6] a simple hybrid
fuzzy logic proportional plus conventional integral controller
for FACTS devices in a multi-machine power system. Z.
Huang, proposed [7] a new power frequency model for
unified power flow controller (UPFC) is suggested with its
DC link capacitor dynamics included. Y. Morioka, proposed
[8] a unified power flow controller (UPFC) miniature model
developed for performing system feasibility studies. Wang
et. al. [9] proposed three types of FACTS-based stabilizers
for
a unified model of a multi-machine power system.
Hingorani presented [10] the control mechanism of real and
reactive power flow in transmission lines using FACTS
controllers.
II. SHUNT CONVERTER CONTROL SYSTEM
Seelam Swarupa,is a PG Student, G V P. College of Engineering,
Visakhapatnam. And K. V. S. Ramachandra Murthy, Associate Professor, G
V
P.
College
of
Engineering,
Visakhapatnam.
Emails:
murthykvs2000@yahoo.co.in
Fig 1 shows the de-coupled control system for the
shunt converter. The D-axis control system controls the dc
link capacitor voltage and the Q-axis control system controls
the UPFC bus voltage /shunt reactive power. The details of
the de-coupled control system design can be found .The de-
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Seelam Swarupa, and K. V. S. Ramachandra Murthy
60
coupled control system has been designed based on linear
control system techniques and it consists of an outer loop
control system that sets the reference for the inner control
system loop. The inner control system loop tracks the
reference.
III. SERIES CONVERTER CONTROL SYSTEM
Fig. 2 shows the overall series converter control
system. The transmission line real power flow is controlled
by injecting a component of the series voltage in quadrature
with the UPFC bus voltage . The transmission line reactive
power is controlled by modulating the transmission line side
bus voltage reference . The transmission line side bus
voltage is controlled by injecting a component of the series
voltage in-phase with the UPFC bus voltage.
Fig. 3: UPFC Connected to a Transmission Line.
Fig. 1 De-Coupled D-Q axis Shunt Converter Control
System.
The in-phase component (VseD) of the series injected
voltage which has the same phase as that of the UPFC bus
voltage, has considerable effect on the transmission line
reactive power (Qline) and the shunt converter reactive
power (Qsh). Any increase/decrease in the transmission line
reactive power (Qline) due to in-phase component (VseD) of
the series injected voltage causes an equal increase/decrease
in the shunt converter reactive power (Qsh). In short,
increase/decrease in transmission line reactive power is
supplied by the shunt converter. Increase/decrease in the
transmission line reactive power also has considerable effect
on the UPFC bus voltage. The mechanism by which the
request for transmission line reactive power flow is supplied
by the shunt converter is as follows. Increase in transmission
line reactive power reference causes a decrease in UPFC bus
voltage. Decrease in UPFC bus voltage is sensed by the
shunt converter UPFC bus voltage controller which causes
the shunt converter to increase its reactive power output to
boost the voltage to its reference value.
Fig. 2 Series Converter Real and Reactive Power Flow
Control System.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Seelam Swarupa, and K. V. S. Ramachandra Murthy
61
Fig. 5 Power system with UPFC.
IV. SIMULATION RESULTS
Fig. 4. Shunt Converter Q-Axis Controller with Reactive
Power Coordination Controller.
The increase in shunt converter reactive power
output is exactly equal to the increase requested by the
transmission line reactive power flow controller (neglecting
the series transformer T2 reactive power loss). Similarly, for
a decrease in transmission line reactive power, the UPFC
bus voltage increases momentarily. The increase in UPFC
bus voltage causes the shunt converter to consume reactive
power and bring the UPFC bus voltage back to its reference
value. The decrease in the shunt converter reactive power is
exactly equal to the decrease in transmission line reactive
power flow (neglecting the reactive power absorbed by the
series transformer T2).
In this process, the UPFC bus voltage experiences
excessive voltage excursions. To reduce the UPFC bus
voltage excursions, a reactive power flow coordination
controller has been designed. The input to the reactive power
coordination controller is the transmission line reactive
power reference. Fig.4S shows the shunt converter Q-axis
control system with the reactive power coordination
controller.
The gain of the washout circuit has been chosen to be
1.0. This is because, any increase/decrease in the
transmission line reactive power flow due to change in its
reference is supplied by the shunt converter. The washout
time constant is designed based on the response of the power
system to step changes in transmission line reactive power
flow without the reactive power coordination controller.
Discrete,
Ts = 5e-006 s.
powergui
A
Aa
Aa
aA
B
Bb
Bb
bB
C
Cc
Cc
L2_50km
Power Plant #1 B1
Pnom=1000 MW
B2
A
B
C
cC
L2_50km1
200 MW
B3
Vabc_B3
Vabc
From3
Iabc_B3
From4
Iabc
PQ
3-phase
Instantaneous
Active & Reactive Power
Scope4
G5
Fig. 6 Simulink Model of UPFC Connected Transmission
Line
A. Response to Step Changes in Reactive Power
Reference
A two machine power system with UPFC is shown in
fig. 6 has been considered to study the response of the
power system to step input changes in reactive power
reference. The analysis is carried out on two different
systems levels. One system is at 230 kV level and the other
is at 345 kV.
Table 1 shows the reduction in peak overshoot of the
reactive power oscillations on 230 kV system when it is
subjected to a step change. Magnitude of step change is
presented in column 3 and Peak over shoot without
controller is presented in column 4 and over shoot with
controller is presented in column 5.
System 1:
Generator ratings : 13.8 kV,1000MVA
Transformer ratings : 13.8 kV/230kV,1000MVA
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Seelam Swarupa, and K. V. S. Ramachandra Murthy
Qinitial
Q
(MVAr)
62
(MVAr)
Step
Change
MVAr
Over shoot
(with
out
coordination
controller)
Over
shoot
(with
controller)
125
75
50
180
147
125
50
75
176
153
125
25
100
173
152
125
-25
150
166
151
125
-50
175
163
150
125
-100
225
164
148
new
Table 2 shows the reduction in peak overshoot of the
reactive power oscillations on 345 kV system when it is
subjected to a step change. Magnitude of step change is
presented in column 3 and Peak over shoot without
controller is presented in column 4 and over shoot with
controller is presented in column 5.
System 2:
Generator: 13.8 kV,1000MVA
Transformer: 13.8 kV/345kV,1000MVA
Qinitial
Q
(MVAr)
Step
Change
MVAr
Over shoot
(with
out
coordination
controller)
Over
shoot
(with
controller)
(MVAr)
125
75
50
180
150
125
50
75
176
145
new
Fig 7 to 10 show the reduction in reactive power
oscillations on 230 kV system. And Fig. 11 and 12show the
reduction in reactive power oscillations on 345 kV system.
Load considered in this work is 200 MW synchronous
motor.
i)
Fig 8 Variation of Qline with step change of
50 MVAr with controller
Fig. 9 shows the variation of reactive power from 125
MVAR to 25MVAR at 0.3 seconds and back to 125MVAR
at 0.6 seconds. The peak over shoot without controller is
observed to be 173 MVAR and with the coordination
controller, it is observed to be 152MVAR. Fig. 10 shows
the variation of reactive power with coordination controller.
Fig. 9 Variation of Qline with step change of 100 MVAr
without controller
Results on 230 kV System :
Fig.7 shows the variation of reactive power from 125
MVAR to 75MVAR at 0.3 seconds and back to 125MVAR
at 0.6 seconds. The peak over shoot without controller is
observed to be 180 MVAR and with the coordination
controller, it is observed to be 147 MVAR. Fig .8 shows the
variation of reactive power with coordination controller.
Fig 10 Variation of Qline with step change of 100 MVAr
with controller
ii) Results on 345 kV System
Fig. 7 Variation of Qline with step change of
50 MVAr without controller
Fig. 11 shows the variation of reactive power from 125
MVAR to 75MVAR at 0.3 seconds and back to 125MVAR
at 0.6 seconds. The peak over shoot without controller is
observed to be 180 MVAR and with the coordination
controller, it is observed to be 150MVAR. Fig. 12 shows
the variation of reactive power with coordination controller.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Seelam Swarupa, and K. V. S. Ramachandra Murthy
63
REFERENCES
[1] S. Kannan, Sesha Jayaram and M. M. A. Salama, “Real and
Reactive Power Coordination for a Unified Power Flow
Controller”, IEEE Transactions on Power Systems, Vol. 19,
No.3, August, 2004, Pg. 1454 -1461.
[2] L. Gyugyi, C. D. Schauder, S. L. Williams, T. R. Reitman, D.
R. Torgerson, and A. Edris, “The unified power flow
controller: A New Approach to Power Transmission Control,”
IEEE Trans. Power Delivery, vol. 10, pp. 1085–1097, Apr.
1995.
Fig. 11 Variation of Qline with Step Change of 50 MVAr
without Controller
[3] C. D. Schauder, L. Gyugyi, M. R. Lund, D. M. Hamai, T. R.
Rietman, D. R. Torgerson, and A. Edris, “Operation of the
unified power flow controller (UPFC) under practical
constraints,” IEEE Trans. Power Delivery, vol. 13, pp. 630–
636, Apr. 1998.
[4] K. K. Sen and E. J. Stacey, “UPFC-UnifiedPower flow
controller: Theory, modeling, and applications,” IEEE Trans.
Power Delivery, vol. 13, pp. 1453–1460, Oct. 1999.
[5]
B. A. Renz, A. S. Mehraben, C. Schauder, E. Stacey, L.
Kovalsky, L. Gyugyi, and A. Edris, “AEP unified power flow
controller performance,” IEEE Trans. Power Delivery, vol. 14,
pp. 1374–1381, Oct. 1999.
[6] P. K. Dash, S. Mishra, and G. Panda, “A radial basis function
neural netwrok controller for UPFC,” IEEE Trans. Power Syst.,
vol. 15, pp. 1293–1299, Nov. 2000.
Fig. 12 Variation of Qline with Step Change of
50 MVAr with Controller
IV.
CONCLUSION
This thesis has implemented a new real and reactive
power coordination controller for a UPFC. The basic control
strategy is such that the shunt converter of the UPFC
controls the UPFC bus voltage/shunt reactive power and the
dc link capacitor voltage. The series converter controls the
transmission line real and reactive power flow. The
contributions of this work can be summarized as follows.
Response of Power System to Step Changes in
Reactive Power Flow Reference has been examined in this
Thesis.
A two bus system is considered with 13.8 kV
generator of 1000 MVA and step up transformer of 13.8
kV/345 kV, 1000 MVA. The step change in the reference
reactive power of 50 MVAr to 225 MVAr has been
introduced in the system and Peak over shoot in the reactive
power oscillations have been observed without the controller
and with the controller. It is observed that there is a 20%
reduction in the peak overshoot by implementing the real
and reactive power coordination controller. Also there is a
improvement in raise time of 30 msec.
[7] P. K. Dash, S. Mishra, and G. Panda “Damping multimodal
power system oscillation using a hybrid fuzzy controller for
series connected FACTS devices,” IEEE Trans. Power Syst,
vol. 15, pp. 1360–1366, Nov. 2000.
[8] Z. Huang, Y. Ni, F. F. Wu, S. Chen, and B. Zhang, “Appication
of unified power flow controller in interconnected power
systems-modeling, interface, control strategy and case study,”
IEEE Trans. Power Syst, vol. 15, pp. 817–824, May 2000.
[9] Y. Morioka, Y. Mishima, and Y. Nakachi, “Implementation of
unified power flow controller and verification of transmission
capability improvement,” IEEE Trans. Power System, vol. 14,
pp. 575–581, May 1999.
[10] Narain G. Hingorani, Laszlo Gyugyi “Understanding FACTS:
concepts and technology of flexible AC transmission systems”,
IEEE Press, 2000.
Swaroopa Seelam graduated from GVP College of Engineering and
is pursuing post graduation from GVP Collegeof Engineering,
Visakhapatnam.
Dr. K V S Ramachandra Murthy did his UG and PG from NIT,
Jamshedpur. He obtained doctorate from JNTU, Kakinada, India.
He is working as Associate Professor in the Department of EEE,
GVP College of Engineering, Visakhapatnam, India.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.K. Dinesh kumar, K.B. Naresh kumar, S. ManiKandan and S. Venkatanarayanan
64
Design of Bridgeless SEPIC Converter for Speed
Control of PMDC Motor
K.K. Dinesh kumar, K.B. Naresh kumar, S. ManiKandan and S. Venkatanarayanan
Abstract: The bridgeless SEPIC converter design is used for the
speed control of permanent magnet DC motor. This paper
focuses the design of Bridgeless SEPIC topology having reduced
switching and conduction losses with improved power factor, It is
designed to work in Discontinuous Conduction Mode (DCM) to
achieve the speed control of DC motor by varying the input supply
to the armature. This converter is investigated theoretically and
the performance comparisons of this proposed converter is
verified with MATLAB simulation. The design example of a low
voltage and PMDC Motor is developed.
Keywords: Bridgeless, Conduction, converter, SEPIC, speed,
switching.
In this proposed work the bridgeless SEPIC converter is
developed for the speed control of PMDC motor. The
Bridgeless SEPIC converter is designed for the energy
elements of Inductors and capacitors. The values obtained are
used in simulation. The conduction and switching losses are
verified. The power factor improvement is verified with
MATLAB simulink. The speed of the motor is controlled
900RPM to 1500RPM. Since the switching time is reduced
and the losses are minimized. This proposed converter carries
full current in the coupling capacitor and hence this capacitor
values to be selected to carry the full load current of the
PMDC.
I. INTRODUCTION
The SEPIC stands for single ended primary inductor
converter. It is a one type of DC-DC converter which is used
in many other applications like mobile phone battery charger,
electronic ballast, telecommunications and DC power
supplies etc, In this converter the output voltage is maybe
buck or boost or same voltage as that of the supply voltage.
The converter have been developed a new ZVS PWM SEPIC
topology. it has low switching and conduction losses due to
zero voltage switching and synchronous rectifier
operation[1]. The SEPIC have been designed to increases the
power factor correction in ac system, in order to achieve the
high power factor [2]. The SEPIC input current and input
voltage have been used to a certain extent, reducing the
amount of lower order harmonics and resulting high power
factor[3]. A new bridgeless PFC SEPIC converter have been
designed for high power factor under universal input voltage
condition[3]. A novel PFC topology have been developed by
the valley-fill circuit into the DCM SEPIC derived converter,
by implementing this topology. The solved the bus capacitor
voltage dependent on the output load issue and avoided high
voltage stress in light load[4]. Two new single–phase
bridgeless rectifiers with low input current distortion and low
conduction losses have obtained by implemented SEPIC
compressed with CUK PFC converter. The size of inductor
was reduced and obtained efficiency of SEPIC converter have
been improved[5].Single switch bridgeless SEPIC converter
have been developed and gave low switching loss compared to
bridgeless double switch converter also efficiency[6].
II. SEPIC CONVERTER
.
The SEPIC stands for single ended primary inductor
converter, which is used to buck or boost or same voltage as
that of supply voltage. The SEPIC output is controlled by
varying duty cycle to the power switches like MOSFET,
IGBT, GTO etc. it is also similar to traditional buck-boost
converter, it has one additional advantage the output is
non-inverted(the output same polarity as the input). Using
series capacitor the couple of energy from input to output and
being capable of true shutdown. when the switch is turned off
the capacitor voltage false to 0V. SEPIC converter is operated
in two mode, one continuous conduction mode (CCM) and
discontinuous conduction mode(DCM). The DCM mode
operation means the inductor current falls to zero.
Fig.1. Schematic diagram of conventional SEPIC converter.
K.K. Dinesh kumar, K.B. Naresh kumar, S. ManiKandan, S. Venkatanarayanan
AP (S G), Email id: kkdinesheee05@gmail.com, nrshkmr325@gmail.com,
manikandan0721@gmail.com, venjeyeee@gmail.com
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Vol. 2, Issue. 1, April-2013.
K.K. Dinesh kumar, K.B. Naresh kumar, S. ManiKandan and S. Venkatanarayanan
65
Fig.2: Current flows during switch is turn on condition
Fig.3: Current flows during switch is turn off condition.
A SEPIC said be in continuous-conduction mode means if
the current through the inductor never falls to zero. During
SEPIC steady state operation While switch S1 is turned on
current IL1 increases and the current IL2 current increase in
negative direction. The energy to increase the current IL1
comes from the input supply since S1 is a short while closed
and the instantaneous voltage VC1 approximately VIN , the
voltage VL2 is approximately –VIN. Therefore, the capacitor
C1 supplies the energy to increase the magnitude of the
current in IL2 and thus increase the energy stored in L2.
When the switch S1 is turned off , the current IC1 becomes
the same as the current IL1, since inductors do not allow
instantaneous change in current. The current IL2 will
continue in the negative direction, in fact it never reverses
direction. It can be seen from the fig.3 that a negative IL2 will
add to the current IL1 to increase the current delivered to the
load.
Fig.4.Permanent magnet DC motor
Fig.5.Construction of permanent magnet in PMDC.
The characteristics of PMDC motor is given below.
III. PERMANENT MAGNET DC MOTOR
Permanent magnet DC motor is similar to an ordinary dc
shunt motor except that its field is provided by permanent
magnet instead of salient pole wound structure. There are
three types of permanent magnet used for such motors, (i.e.)
Alnico, ferrite and rare-earth magnets. These materials has
high residual flux density and high coercivity, The armature
consist of slots to the accommodated armature winding. In
this type of motor field speed control is not possible but
armature speed control is only possible in order to vary the
input supply to the armature winding the motor speed is
varying as much we desired value. In this type of motor below
speed control only possible because of field having permanent
magnet, suppose we increase the voltage above rated voltage
means the motor insulation will become into failure and
motor
windings
will
be
short
circuited.
Fig.6.Charteristics of PMDC motor.
IV. BRIDGELESS SEPIC CONVERTER
A conventional AC-DC SEPIC converter had a bridge
circuit in input because this circuit converts ac-dc. The
converting process was done by means of diodes. During
positive half cycle couple of the diode was conducting and
negative half cycle another couple of the diode was
conducting due to this conduction loss also increases and also
presence of power switches the switching loss is increase. It is
an unavoidable one but conduction loss is avoidable one. A
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.K. Dinesh kumar, K.B. Naresh kumar, S. ManiKandan and S. Venkatanarayanan
bridgeless SEPIC converter gives a low conduction loss and
switching loss during switch turn on and turn off condition.
The bridgeless circuit also used to improve power factor in
SEPIC converter during conversion of ac-dc. Here three
identical inductor is used to reduce the ripple current and
coupling capacitor is used to store the input voltage and boost
voltage both capacitors are identical so that the voltage ripple
also reduced. During positive half cycle all components will
conduct except DS1, S2, C2, L3 and D02. During negative
half cycle all components will conduct except DS2, S1, C1,
L2 and DO1. Thus only eight components will be conducted
at each half cycle compared to eleven in bridgeless SEPIC
converter. In this circuit PID controller is used to vary the
speed of the PMDC motor by varying pulse width to the
SEPIC converter, we obtained the various voltage to the
motor.
Fig.7.Bridgeless SEPIC converter circuit diagram.
66
Fig.9.During negative half cycle, switch Q2 turn on and Q1 turn off
condition.
V. CIRCUIT OPERATION
The operation of the converter will be explained assuming
that the three inductors are working in DCM. Operating the
SEPIC in DCM offers advantages over continuous-current
mode (CCM) operation. Such as a near-unity power factor
can be achieved naturally and without sensing the input line
current. Also in DCM, both Q1 and Q2 are turned on at zero
current. While the diode DS1 are turned off at zero current.
Thus, the loss due to switching losses and the reverse recovery
of the rectifier are considerably reduced.
Fig.10(a).During positive half cycle, switch Q1 turn on and Q2 turn
off condition.
(a) MODE 1: During the positive half-line cycle, the first
dc-dc SEPIC circuit, L1-Q1-C1-L3-Do, is active through
diode Dp, which connects the input ac source to the output
ground. when the switch Q1 is turned on, diode Dp is forward
biased by the sum inductor currents iL1 and iL2. As a result,
diode DN is reversed biased by the input voltage. The output
diode is reversed biased by the reverse voltage (Vac + Vo). In
this stage, the three-inductor currents increase linearly at a
rate proportional to the input voltage Vac.
Fig.8.During positive half cycle, switch Q1 turn on and Q2 turn off
condition.
(b) MODE 2: During the negative half-line cycle, the second
dc-dc SEPIC circuit, L2-Q2-C2-L3-Do, is active through
diode DN, which connects the input ac source to the output
ground.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.K. Dinesh kumar, K.B. Naresh kumar, S. ManiKandan and S. Venkatanarayanan
67
1) Input voltage Vac =12 Vrms at 50Hz
2) Output voltage = Vo=15Vdc
3) Output power = 30Watts
4) Switching frequency = 330KHz
5)Maximum input ripple current∆ = 20%
fundamental current
6) Output voltage ripple ∆ = ±1% Fig.10(b).During positive half cycle, switch Q1 turn on and Q2 turn
off condition
At the instant, switch Q1 is turned-off, diode Do is
turned-on simultaneously providing a path for the three
inductor currents. Diode Dp remains conducting to provide a
path for iL1 and iL2. In this stage, the three inductor currents
decrease linearly at a rate proportional to the output voltage,
Vo.
(c)MODE 3: In this stage, both Q1 and Do are in their
off-state. Diode Dp provides a path for iL3. The three
inductors behave as current sources, which keep the currents
constant. Hence, the voltage across the three inductors is zero.
Capacitor C1 is charging up by iL1, while C2 is discharged by
iL2.
Fig.11. shows the main theoretical waveforms during one
switching period Ts. It should be mentioned here that if the
two active switches Q1 and Q2 are implemented as standard
MOSFET, then the body diode of Q2 will conduct during the
first stage and the circuit will not function properly. In other
words, there are reverse voltages applied to the active
switches, so that the switches must have reverse blocking
capability. Therefore, unidirectional current conducting
device must be implemented for Q1 and Q2. In this case,
turning ON or OFF Q2 during the first stage will not change
the circuit operation mode. Accordingly, both of the switches,
Q1 and Q2, can be driven by the same control signal, which
helps in reducing the cost and complexity of the driving
circuit.
The voltage conversion ratio M is
15
=
= 0.88(4)
12 ∗ √2
The value of
is
1
<
=
= 0.147(5)
2( + 1)
For values of
>
, the converter operates in CCM;
otherwise, the converter operates in DCM.
Inductance Le value is
=
= 2.22µ (6)
2
Inductances L1,L2 and L3 value can be determined as follows,
=
=
,
=
is given by
(2)
= 10
∆
=
,(7)
2
= 100
(8)
−
The required output capacitance to maintain peak-peak
output voltage ripple of 2% of Vo can be calculated as follows,
1
1 1
1
+ −
(9)
2
2
And Co1, Co2 =1mF
∆
=
The coupling capacitor C1 must be chosen such that its
voltage Follows the shape of the input ac line voltage wave
form with the lowest ripple as possible, C1 should not cause
low-frequency oscillations with inductors L1,L2 and L3,
based on three constraints , the value of C1=C2=10mF is
chosen for this particular design.
The inductor ripple current is,
̅
The rate of increase of the three inductor currents are given by
=
, = 0,1,2,3(1)
The peak switch current
of
̅
=
=
1+
2
2
=
+ (10)
1
2
The current
Where,
1
1
1
1
= + + (3)
2
−
1
−
1
−
(11)
simply found by following expression,
1−
1+
2
(12)
can be represented by,
And D1 is the switch duty cycle. This intervals ends when
Q1 is turned off, initiating the next subinterval.
̅
=
cos(
)(13)
VI. DESIGN PROCEDURE FOR BRIDGELESS SEPIC
A simplified design procedure is presented in this section
to determine the components values of the proposed
converter. Suppose we would like to design the SEPIC
converter with the following power stages specification.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.K. Dinesh kumar, K.B. Naresh kumar, S. ManiKandan and S. Venkatanarayanan
68
Fig.13.Capacitors C1 and C2 voltage waveforms.
Fig.14.Inductors L1 and L2 voltage waveforms.
Fig.11. Theoretical waveforms in DCM of proposed converter
VII. SIMULATION
A simulation performed at bridgeless SEPIC converter
inductors and capacitors values are taken above mentioned
value, Supply voltage and switching frequency are also
specified value. The bridgeless SEPIC converter simulated
waveforms are shown in fig.
Fig.15. Input voltage and current waveforms.
Fig.12.Inductors L1, L3 and L2 current waveforms.
Fig.16. Output voltage and current waveforms.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.K. Dinesh kumar, K.B. Naresh kumar, S. ManiKandan and S. Venkatanarayanan
b. Motor specifications
Sl.no.
1.
2.
3.
4.
5.
Parameter
Ra, La
Torque constant
J
Bm
Tf
Value
0.5Ω, 0.01H
1.8 N.m/A
0.05 Kg.m^2
0.02 N.m.s
0 N.m
Torque constant (N.m/A)
J-total inertia in Kg.m^2
Bm-viscous friction coefficient in (N.m.s)
Tf-coulomb friction torque in (N.m)
Where,
Ra-armature resistance in Ω
La-armature inductance in H
69
Zheng Zhao, Student Member, “A Novel Valley-Fill
SEPIC-derived Power Supply”, ieee transactions on power
electronics, vol. 27, no. 6, june 2012.
[5] Ahmad J. Sabzali, Esam H. Ismail, and Mustafa A. Al-Saffar
Member, IEEE, Senior Member, IEEE, Member, IEEE Abbas
A. Fardoun Senior Member, IEEE.
[6] Hyunsoo Koh, “Modeling and Control of Single Switch
Bridgeless SEPIC PFC Converter
K.K. DINESH KUMAR was born in India,
Madurai in 1992 is pursuing in K.L.N. college of
engineering, madurai as final year student in the
department of EEE. His area of interest is
converter control, Power Electronics, DC-DC
converters, Power supplies, Power factor correction etc
S. MANIKANDAN was born in India, Madurai in
1992 is pursuing in K.L.N. college of
engineering, madurai as final year student in the
department of EEE. His area of interest is
converter control, SEPIC converter and Power
Electronics,DC-DC converters.
K.B. NARESH KUMAR was born in India,
Madurai in 1992 is pursuing in K.L.N. college of
engineering, madurai as final year student in the
department of EEE His area of interest is
converter control, DC-DC converters, Power
supplies, Power factor correction.
VIII. CONCLUSION
The bridgeless SEPIC converter designed used for the
speed control of permanent magnet DC motor. This paper
Bridgeless SEPIC topology is used and having reduced
switching and conduction losses with improved power factor,
It is designed to work in Discontinuous Conduction Mode
(DCM) to achieve the speed control of DC motor by varying
the input supply to the armature. This converter is developed
in MATLAB simulink and Performance are verified. The
efficiency of this converter is obtained about 82.2%. The
further improvement can be done in DSP controllers.
REFERENCES
S.VenkatanarayananAP(S.G) was born in India ,Vandary,Madurai
in 1969, He Received BE Degree in 1998 at
Madurai Kamaraj University Madurai , ME in
2008 at Annauniversity Chennai, Also he is
have MBA and MPhil ,Presently pursuing his
part time Ph.D at Annauniversity .He is
working as Assistant Professor (Sr.Gr) at
K.L.N. college of engineering, Pottapalayam,
Sivagangai District in the department of EEE.
His area of interest is converter control, SEPIC converter and
Power Electronics,DC-DC converters, Power supplies, Power
factor correction etc and development of prototypes of converters
[1]
In-Dong Kimy, Jin-Young Kim, Eui-Cheol Nho, and
Heung-Geun Kim “Analysis and Design of a Soft-Switched
PWM Sepic DC-DC Converter” Journal of Power Electronics,
Vol. 10, No. 5, September 2010,pp.461-467.
[2] T. Raghu, S. Chandra Sekhar, J. Srinivas RaoJ. “SEPIC
Converter based-Drive for Unipolar BLDC Motor”
International Journal of Electrical and Computer Engineering
(IJECE) Vol.2, No.2, April 2012, pp. 159~165.
[3] M. R. Sahid, A. H. M. Yatim, Taufik Taufik I, “A New AC-DC
Converter Using Bridgeless SEPIC” 2010 IEEE.
[4] Hongbo Ma, Student Member, IEEE, Jih-Sheng Lai, Fellow,
IEEE, Quanyuan Feng, Senior Member, IEEE, Wensong Yu,
Member, IEEE, Cong Zheng, Student Member, IEEE, and
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
70
Apoorva Saxena and Subhash Chandra
Rural Off Grid Electrification Using Hybrid
Mini grid and its Socio Economic Impact
: A Case Study of District Pilibhit
Apoorva Saxena and Subhash Chandra

Abstract— Despite the best efforts of the governments of
various countries to promote rural electrification, it is not enough
to keep in pace with rapid urban and industrial growth. In
remote areas, off grid technologies combined with sustained
financial management can lead to environment friendly access to
electricity by rural population. This paper explores the socioeconomic impact of rural electrification, various technical
approaches for rural electrification with focus on Hybrid minigrid & financial model for sustained low cost operation of hybrid
mini-grid involving skilled village population.
Index Terms—Rural electrification, Hybrid mini-grid
architecture, scope analysis, community based implementation
model.
M
I. INTRODUCTION
odern energy services are crucial to human well being
and play an important role in the economic and social
development of the country. Significant efforts have been
made globally to provide electricity to both urban & rural
population. In this regard, global electrification rate went from
49 % in 1970 to 80.5 % in 2011 with around 5.2 billion people
having access to electricity [1].Despite this, over 1.3 billion
people worldwide are still without access to electricity. An
estimated 80 % of these people live in rural areas with
majority of them having scant chances of accessing electricity
in near future. More than 95 % of these people reside either in
Sub-Saharan Africa or developing Asia [1].
In developing Asia, it is projected that number of people
without access to electricity will come down by 45% from 675
million people in 2009 to 375 million in 2030[1] through
government sponsored schemes of grid extension.. But still
rural population will make majority of people which will not
be having access to electricity. One more point to consider is
regarding Quality of the service. Grid extension increases the
demand but if it is not accompanied with corresponding
increase in generation( which is most likely case in majority of
1.Apoorva Saxena is working as Assistant Professor in Department of
Electrical Engineering with GLA University, Mathura, India (phone:
9997624727; e-mail: apoorvatu@gmail.com.
2.Subhash Chandra is working as Assistant Professor in Department of
Electrical Engineering with GLA University, Mathura, India (phone:
7830775997; e-mail: 2003subhash@gmail.com.
Asian countries), adding new customers only aggravates the
problem of electricity outages and will ultimately lead to
lesser number of hours for which electricity will be available.
An Action-Aid study [2] takes our attention to an interesting
fact regarding rural electrification in India. According to the
report, the installed capacity of coal-fired power plants in
India increased from 74429 MW in 2002 to 96,794 MW in
2009.Along with this increase in 22365 MW in coal based
energy, 10,000 MW of hydro power capacity was also added
between 2002 and 2009.During the same time period number
of un-electrified villages came down marginally from 52 % in
2002 to 45 % in 2009 which counts to the electrification of
20,000 villages. Further, out of these 20,000 villages
electrified, 2000 villages were electrified through decentralized renewable energy system. So renewable energy
contributed around 2% of those reductions in un-electrified
villages. On the other side, despite addition of over 33,000
MW of coal fired power plants & large hydropower, they
contributed only 5 % in the rural electrification. So inference
that can be taken out from this is that the addition of electricity
generation for conventional power plants has not addressed
the issue of electricity access to the poor rural population.
Fig.1.Location of coal based plants & rural electrification
scenario [2]
The maps shown above clearly indicate that the area which
has highest concentration of thermal power plants has dismal
1-10 % of rural electrification rate (shown in red). This clearly
justifies our inference above & underlines the need to look
something beyond just extending the national grid to rural
areas.
Looking into this scenario, major technological challenge is
how to deliver sustainable electricity services to these rural
populations. Given the relatively small loads, topographical
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
71
Apoorva Saxena and Subhash Chandra
constraints-isolated “Hybrid Mini grid” can attain a greater
penetration, far beyond those which can be achieved in large
scale grids in the near future. This point will be elaborated
further in this paper.
The goal of this paper is to explore the positive impacts of
rural electrification and how it can lead to social upliftment
& gender equality among poor communities at village level,
contribute to the knowledge base of hybrid mini grids and
analyze the scope of implementing hybrid mini-grids in
district Pilibhit taking into consideration available local
resources. This paper is organized as follows: Section II
describes implications of rural electrification, Section III
details the various technical approaches to bring electricity to
rural areas with special focus on hybrid mini grids, Section IV
discusses the scenario regarding installation of Hybrid Mini
grids in district Pilibhit & Section V discusses the effective
business model that could be adopted for sustainable operation
of Hybrid mini grid.
II. IMPLICATIONS OF RURAL ELECTRIFICATION
Access to electricity leads to some direct benefits like higher
productivity of agriculture products [3] and some indirect
benefits like improved knowledge of weather conditions and
crop prices due to access to televisions and radios.
Electrification will be necessary in achieving any of the goals
laid down by the Government of India in 12th five year plan. It
can help to reduce child mortality rate through refrigeration of
vaccines which will be available at village panchayat levels. It
can help to achieve universal primary education by improving
evening study conditions.
Application of end-use energy technologies like food
preservation and processing, electric appliances for grinding ,
local craft production would encourage home based women
micro enterprises which can contribute significantly to house
hold incomes[4].Electrification can thus enhance social
welfare through augmented incomes.
In rural Asia 1.9 billion men and women relies on wood,
charcoal and dung as a major source of energy especially for
cooking purposes.These methods of energy production are
highly inefficient and poses significant health risk. As per
World Health Organization (WHO) projections, the number of
people who die prematurely each year could be over 1.5
million by 2030, which will be around 35 % more compared
to death caused by malaria & HIV/AIDS combined
together[4].
To promote the fuel transition in rural Asia from unhealthy
fuel-wood and traditional bio-mass to electric based /
improved bio-gas technology key factor would be to increase
the income level of women working as a labor that would
ultimately lead to economic worth in the use of women as a
labor. This could act as a strong incentive to economies on
women’s unpaid labor time in fuel collection and other
household activities, encouraging use of clean, efficient
sources of energy. So rural electrification can be a major
driving force in attaining good health for children & women &
can also lead to gender equality in rural India by empowering
rural women.
III. TECHNICAL APPROACHES FOR RURAL ELECTRIFICATION
There are three basic technical approaches to bring electricity
in rural areas [5]:
(a) Extension of national grid
(b) Isolated off-grid using renewable energy
(c) Hybrid mini grid
First option deals with simply extending the national grid to
remote locations. But this approach of rural electrification is a
challenging task because it involves delivery of a service to
the people that are remote, dispersed and with low electricity
consumption. This means that on one side the customer base is
generally poor and less able to pay the full cost of the service
and on the other side extending the transmission line to these
remote, tough terrains include high expansion cost [4]
.Combining both of these factors, it is imperative that to
expect extension of grid to the un-served rural population in
near future is a distant reality.
The second option depends mainly on the dispersion of the
household and type of load required. In these stand alone
systems, power generation is installed close to the load and
hence transmission and distribution costs are minimized.
However the total cost of energy tends to be higher due to lack
of subsidies.
The third option deals with a distribution network spread in a
localized area covering one or two villages and using at least
two different non renewable technologies (PV panels, small
hydro plants, biogas plants, wind turbines etc) for power
generation with a diesel driven generator acting as a back-up.
The combination of renewable energy sources with diesel
driven generator has proven to be the least – cost solution as
the advantage and benefits of every energy resource
complement each other, with solar PV collectors
complementing wind power during the month with less wind
or picking up when hydro-generation drops during the dry
season.
Fig.2. AC bus bar coupled Hybrid mini-grid [6]
A Hybrid mini grid is composed of three subsystems:
generation, distribution and demand [7].The structure of each
sub-system depends on the availability of resources & user
characteristics.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
72
Apoorva Saxena and Subhash Chandra
A. Generation
This sub-system comprises of renewable based generation,
storage devices, converters and energy management system of
Hybrid mini-grid.
Taking total wet manure per animal per day/ Kg as 35 of
which 4.5 Kg. is the total solid content [10], the total electrical
energy output and digester volume will be calculated while
designing the hybrid mini-grid
B. Distribution
This subsystem is responsible for distribution of energy to the
end user via mini grid. For the case discussed in this paper, we
propose the use of single phase alternating current system.
This decision will have direct impact on the cost of the project
and appliances that can be used.
C. Resources for Hydro-energy
In terms of water resources, this area has 17 rivers including
major rivers like Sharda & Gomti [11] and has a total canal
length of 938 Km [11] .
C. Demand
This subsystem includes all the end user side equipments such
as meters , wiring and equipments which will run on power
generated by hybrid power plant.
IV. IMPLEMENTAION SCOPE ANALYSIS FOR PILIBHIT
A. Adjusting to local resources available
Renewable energies are highly location specific in nature. So
any specific hybrid energy technology should be selected
according to the availability of different renewable sources in
a particular region.
Animal husbandry is very popular in this district due to the
availability of 78639 hectares of large dense forest[9] and
accessibility of fodder in the nearby forest. The number of
livestock present in the district is given in table below [9]
Cattle
Cows
Buffaloes
Goats
Pigs
Poultry
Numbers
154633
264822
99735
11091
95805
So it can be concluded that due to large number of cows and
buffaloes, there is a sufficient availability of cow dung in the
region which can act as a raw material for biomass plant
B. Calculation for digester sizing
The energy available from a biogas digester is given by [10]
(1)
E   H bVb
where  is combustion efficiency of boiler
H b is the heat of combustion per unit volume of biogas
Vb Volume of the bio-gas
Also, Vb  cm0
(2)
where c is biogas yield per unit dry mass of whole input
m0 is the mass of dry input.
With the help of these data, volume of fluid in the digester
(Vf) can be calculated. Hence volume of the digester is given
by
Vd = Vf ( flow rate) . t (retention time in digester) (3)
Name of the channel
Sharda Canal
Hardoi Branch
Kheri Branch
Sharda Sagar feeder
Outlet channel
Subsidiary Hardoi Branch
Length (in Km)
12.64
36.80
31.20
3.9
3.23
21.55
Looking into this scenario, there could be a major possibility
of having micro hydro power plants in this region.
The assessment of both biomass energy & hydro-energy
clearly indicates that a hybrid mini grid with biomass and
micro-hydro as energy sources will be ideally suited for
designing a self sustained, cost effective hybrid power
distribution network in this region.
V. PROPOSED BUSINESS MODEL
A. Community based Model
Hybrid mini grids are usually located in remote isolated areas
and hence does not attract private-sector /utility interest due to
obvious commercial reasons. So we propose a Community
based mini grid model in which community becomes the
owner and operator of the system and provide maintenance,
tariff collection and management services. In a community
based organization, the owners/managers are also the
consumers and hence they have strong interest in the quality
of the service and on the other side generate O & M jobs for
local poor people in the community.
However, there are some challenges facing this socio-business
structure [5]. First of all, local communities lack the technical
skills to design, install & maintain the system and business
skills to formulate & calculate tariff structure. So this
community based model requires substantial technical
assistance with regard to system installation, operation &
maintenance of Hybrid mini grid which can only be
implemented through participation from Central/State
government.
Second challenge facing this community based model is to
measure and limit the consumption of each user to avoid
potential conflicts within the community. Hence the
committee which will be in-charge of the system management
has to be constituted keeping in view the social structure of the
area and with due consent of local leadership. Therefore, it is
clear that if a community-based organization is to be
successful, it requires time, nurturing, and capacity building.
Sometimes, it may be more efficient to involve a private or
public entity that will take on the technical aspects and
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
73
Apoorva Saxena and Subhash Chandra
therefore limit the community organization’s role to
monitoring.
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Fig.3. Proposed Business Model
VI. CONCLUSION
Hybrid mini grids can help to increase the rural electrification
rate along with reliable power supply as compared to off- grid
single source stand alone system. This is due to the fact that
availability of power is ensured even when one of the
generation sources faces intermittence. Biogas digesters and
biomass gasifiers are particularly promising from the
economic perspective, given their high capacity factors and
availability in size ranges matched to mini grid loads. Mini
grid system are also becoming economically viable option as
the cost of renewable energy shows downward trend and fuel
prices increases . Despite these opportunities, penetration of
hybrid mini grid in most of the countries remains low. Some
of the reasons behind this could be use of poor quality or
untested technologies, insufficient funding or lack of
subsidies.
Poor assessment of local conditions often compounded by lack
of local data is also the major cause of failure in many of the
cases. Development of schemes without attention to
developing supplementary programmes dealing with issues
such as access to markets, SME development and working
with local financing institutions, has contributed to a lack of
demand and an inability to sustain the schemes.
So for long term viability of the system it is imperative to
include local leaders in decision making process and
encourage local rural population in the
operation &
maintenance of hybrid mini-grid. This community based
model of rural electrification could have myriad of positive
impacts on the socio-economic conditions of the rural
community and can ultimately lead to gender equality among
the rural communities. However, serious training programs
should be developed to compensate for the lack of skills
among local peoples with participation from Central/State
Government.
[10]
[11]
the poor: The clean energy option, for Action Aid, pp.15-17.
Hisham Zerriffi, Rural Electrification-strategies for distributed
generation, Springer 2011 pp.3-4
Reihana Mohideen “ Implications of clean & renewable energy
development for gender equality in poor communities in south-east
Asia” IEEE 2012
Alliance for rural electrification(ARE)-Hybrid Mini grids for rural
electrification: lessons learned pp. 10-14,
Arif Md. Waliullah Bhuiyan, Kazi Shariful Islam, Muhammad Mohsiul
Haque, Md. Rejwanur Rashid Mojumdar, and Md. Mahfuzu Rahman ,
”Community-Based Convenient Hybrid Mini-Grid : Implementation
Proposal and Analysis for Bangladesh ,” International Journal of
Innovation Management and Technology, Vol. 2, No. 5, October
2011.
International Energy Agency, Social, Economic & Organizational
Framework for Sustainable operation of PV hybrid systems within Minigrids 2011.
Brief industrial profile of district Pilibhit, Ministry of MSME, Govt. Of
India
Base Line survey in the minority concentrated districts of Uttar
Pradesh, sponsored by Ministry of minority affairs, Govt. of India ,
2008 pp.5
John Twidell &Tony Weir, Renewable Energy Resources - II
edition, Taylor & Francis group pp.383-384
www.pilibhit.nic.in
Apoorva Saxena has received his M.E. degree in Power
System & Electric Drives from Thapar University, India in
2008. He has completed his B.E. degree in Electrical &
Electronics Engineering from GLA Institute of Technology &
Management, Mathura, India in 2003. Currently, he is
working with GLA University, Mathura, India as Assistant
Professor in Electrical Engineering Department. His current research area
includes clean energy & Smart Grid Technologies. E-mail:
apoorvatu@gmail.com.
Subhash Chandra has received his M. Tech. degree in
Power System & Drives from YMCAIE, Faridabad, India in
2009. He has completed his B. Tech. degree in Electronics
Engineering from AIET, Lucknow , India in 2003. Currently,
he is working with GLA University, Mathura, India as
Assistant Professor in Electrical Engineering Department. His research
interest include Clean Energy & Application of Power Electronics in
Renewable Energy. E-mail: 2003subhash@gmail.com.
REFERENCES
[1]
[2]
International Energy Agency, World energy outlook 2011
Bast, Elizabeth and Srinivas Krishnaswamy, 2011. Access to energy for
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.Sandhya, Dr.A.Jaya Laxmi and Dr.M.P.Soni
74
Optimal Placement of Distribution Generation in
Radial Distribution System
K.Sandhya, Dr.A.Jaya Laxmi and Dr.M.P.Soni
Abstract: In this paper the methodology to find the optimal size
and location of distribution generation in radial distribution
system is presented. The load flow technique for radial
distribution system is proposed. The backward-forward sweep
method is used to carry load flow analysis. The proposed
methodology is applied on IEEE 33-bus test system. The results
include the comparison of voltage profile and power flows
before and after placing the DG.
II. LOAD FLOW
In any radial distribution network, the electrical equivalent
of a branch-i, which is connected between nodes 1 and 2
having resistance r(i) and inductive reactance x(i) is shown in
Fig.1.
Keywords: Distribution Generation, Distribution System,
Load Flow and Voltage Profile.
I. INTRODUCTION
With the restructuring of Power Systems and with shifting
trends towards distributed and dispersed generation, the issue
of Power Quality is going to take newer dimensions. The
share of DGs in power system worldwide is increasing and
their contribution in the future power system is expected to be
even more. Energy policies worldwide are encouraging
installation of DGs in both transmission and distribution
networks along with large scale power generating plants.
The general belief is that the future of the power
generation will be DGs. But the fact is that the distribution
systems were not planned to support the installation of active
power generating units in them. DGs come with opportunities
as well as challenges. They, in one hand, are expected to be
the solution of most of the power system problems while, on
the other hand, they are adding new problems. Their grid
connection, pricing, change in protection scheme are the
name of the few. Still maximum benefit from this new power
generation technology can reap if it is handled properly.
Hence, utilities and distribution companies need tools to place
small generating units in their distribution systems.
Fig.1. Electrical equivalent of a typical branch-i
From Fig.1 current flowing through the branch-i is given by
 P (Re( i ))  j * Q (Re( i )))
I (Re( i ))  
V (Re( i ))

*
... (2.1)
where,
Se(i) = Sending end node
Re(i) = Receiving end node
Let
I(i)=I(Re(i))
… (2.2)
V(Re(i)) = Voltage magnitude at branch i
V(Re(i))=V(Se(i))-I(i)×(R(i)+jX(i))
… (2.3)
where,
R = Resistance of branch i
X = Reactance of branch i
The active and reactive power losses in branch i are given
by
2
P (i) = I (i ) × R (i )
2
Q (i) = I (i )  X (i )
K.Sandhya is working as Research Scholar, Department of Electrical and
Electronics Engineering, JNTU College of Engineering, Hyderabad, AP,
INDIA. sandhyakp_msr@yahoo.co.in, Dr.A.Jaya Laxmi is worjing as
Associate professor, Department of Electrical and Electronics Engineering,
JNTU College of Engineering, Hyderabad, AP, INDIA. ajl1994@yahoo.co.in
and Dr.M.P.Soni is working as Professor and Head, Department of Electrical
and Electronics Engineering, MJ college of Engineering and Technology,
Banjarahills, Hyderabad, AP, INDIA, drmpsoni@yahoo.com



… (2.4)
…(2.5)
ln = number of branches
nd = number of nodes
Normally the substation voltage V(i) is known and is taken
as│V(1)│=1.0 (p.u) Initially, P(i) and Q(i) are set to zero for all
i. Then the initial estimate of P(2) and Q(2) will be the sum of
the loads of all the nodes beyond node 2 plus the local load of
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.Sandhya, Dr.A.Jaya Laxmi and Dr.M.P.Soni
75
node 2. For all the branches i = 1,2,…….,nd-1 , compute
P(i+1) and Q(i+1) . Compute │V(i=1)│, P(i) and Q(i) using Eqns.
(2.3), (2.4) and (2.5). This will complete iteration. Update the
loads P(i+1) and Q(i+1) (by including losses) and repeat the
same procedure until all the voltage magnitudes are computed
to a tolerance level of 0.0001 p.u. in successive iterations.
Once all the nodes and branches are identified, then
voltage magnitudes of all the nodes are calculated by using
the Eqn. (2.3). It is necessary to obtain the exact feeding
through all the receiving end nodes and the voltage
magnitudes of all the nodes as the voltage of the substation is
known (V(1)). Then compute the branch losses using Eqns.
(2.4) and (2.5). The convergence criterion is that if the
magnitude of voltage difference of successive iterations is less
than the error (i.e., 0.0001) value, the solution is converged.
The backward-forward sweep method is used to carry load
flow analysis.
consumed by a DG (wind turbine generator) in a simple form
can be represented by Equ. (3.5).
2
Q DG   ( 0 . 5  0 . 04 PDG
)
Now the real loss equation can be written as
2
n n  A [( P

ij
DGi  PDi )Pj  (1  0.04PDGi  QDi )Q j ]
PL   

2
i 1 j 1  Bij [(1  0.04PDGi  QDi ) Pj  ( PDGi  PDi )Q j ]


n
PL
 2 Aii (Pi  0.08PDGiQj )  2Bij (0.08PDGiPj  Qj )  0
PDGi
j 1
2
 Aii [ PDGi  PDi  0.08 PDGi ( 0.05  0 .04 PDGi
 Q Di )]  
 n

n
 ( A P  B Q )  0 .08 P


ij j
ij
j
DGi  ( Aii Q j  B ij P j )  0
 j 1

j 1
j 1
 j  i

X

i
PG = PD + PL
n
n
... (3.1)
... (3.2)
Y
B ij
ij
P
j
 B
ij


( A ii Q
j
 B
ij

)


P j) 


Q
j
... (3.8)
... (3.9)
Equ. (3.8), thus, can be written as
3
0.0032AiiPDGi
 PDGi[1.004Aii  0.08AiiQDi  0.08Yi ]  ( Xi  AiiPDi )  0
... (3.10)
If the above equation is solved for PDGi , it will be
known that the amount of real power that the wind turbine
has to produce at various locations so as to minimize the real
loss. This will solve the sizing problem and placement
problem is solved by comparing the losses by putting DG of
corresponding optimal sizes at various locations. The bus at
which the total loss is minimum and corresponding size will
be the optimal location and size, respectively.
... (3.3)
IV. RESULTS
where
R ij Cos (  i   j ) 

V iV j


R ij Sin (  i   j ) 


V iV j

i
j 1
j1
i 1 j 1
A ij 
( A
n
where, PL is the real power loss in the system, PG and
PD are its power generation and demand, respectively.
PL   Aij ( Pi Pj  Qi Q j )  Bij (Qi Pj  Pi Q j )

j 1
j i
III. PLACEMENT OF DG
Min PL
Such that
... (3.7)
j 1
n
The objective function can be written as:
.. (3.6)
The necessary condition for minimum loss is:
Let,
The objective of the placement technique is to minimize the
real power loss. The DG supplies real power and absorbs
reactive power so the bus where the DG is installed has to be
treated as a load bus. Most of the wind turbines have the
similar characteristic, so the location at which they are
connected has been treated as load buses while performing
load flow analysis.
... (3.5)
... (3.4)
Pi and Qi are net real and reactive power injection in bus
‘i’, respectively.
Rij is the line resistance between buses ‘i’ and ‘j’.
Vi and  i are the voltage and angle at bus ‘i’,
respectively.
For wind turbines, induction generators are used to
produce real power and reactive power will be consumed in
the process. The amount of reactive power they consume is a
function of the active power output. The reactive power
The computer programs have been developed in
MATLAB software to examine the efficiency of the proposed
approach. The proposed work is tested on 33-bus radial
distribution system with a load of 3.72 MW and 2.3 MVAR.
The proposed method is illustrated with 33 bus test system.
Bus No. 1 is the source node connected to the transmission
system while Branch 1 refers to the branch connecting Bus
No. 1 to Bus No. 2. Based on the proposed methodology, the
optimal DG sizes for all the buses are found in terms of their
optimal real power production and corresponding reactive
power consumption. The proposed algorithm is tested for
solving IEEE-33 node systems whose single line diagram is
shown in Fig. 2. The line, load data is shown in Table 1.
The voltages obtained before placing DG and after
placing DG are tabulated in Table 2. From the results it can be
observed that the voltages obtained from after placing DG is
greater than before placing DG and the active power losses
reduced from 202.50KW to 132.29 KW which results in
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.Sandhya, Dr.A.Jaya Laxmi and Dr.M.P.Soni
76
34.6716 % real power loss reduction and the reactive power
losses reduced from 135.13 to 88.40 KVAR which results in
34.5815 % reactive power loss reduction and minimum
voltage is increased to 0.94947 from 0.91306 (p.u).
Table.1.The line and load data for 33-node radial distribution system
Branch
Number
Sending
end Node
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
2
19
20
21
3
23
24
6
26
27
28
29
30
31
32
Base MVA = 100
Receiving
end
Node
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Resistance
R ()
Reactance
X()
0.0922
0.4930
0.3660
0.3811
0.8190
0.1872
0.7114
1.0300
1.0440
0.1966
0.3744
1.4680
0.5416
0.5910
0.7463
1.2890
0.7320
0.1640
1.5042
0.4095
0.7089
0.4512
0.8980
0.8960
0.2030
0.2842
1.0590
0.8042
0.5075
0.9744
0.3105
0.3410
0.0470
0.2511
0.1864
0.1941
0.7070
0.6188
0.2351
0.7400
0.7400
0.0650
0.1238
1.1550
0.7129
0.5260
0.5450
1.7210
0.5740
0.1565
1.3554
0.4784
0.9373
0.3083
0.7091
0.7011
0.1034
0.1447
0.9337
0.7006
0.2585
0.9630
0.3619
0.5302
Active
power
(kW)
100.00
90.00
120.00
60.00
60.00
200.00
200.00
60.00
60.00
45.00
60.00
60.00
120.00
60.00
60.00
60.00
90.00
90.00
90.00
90.00
90.00
90.00
420.00
420.00
60.00
60.00
60.00
120.00
200.00
150.00
210.00
60.00
Reactive
power
(KVAr)
60.00
40.00
80.00
30.00
20.00
100.00
100.00
20.00
20.00
30.00
35.00
35.00
80.00
10.00
20.00
20.00
40.00
40.00
40.00
40.00
40.00
50.00
200.00
200.00
25.00
25.00
20.00
70.00
600.00
70.00
100.00
40.00
Base KV = 12.66
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.Sandhya, Dr.A.Jaya Laxmi and Dr.M.P.Soni
77
Fig. 2. Single line diagram of 33-Bus radial distribution system.
Table 2. Voltages obtained for 33-Bus system
Voltage (p.u)
Node No.
Voltage (p.u)
After placing
DG
1.00000
Node No.
1
Before
placing DG
1.00000
2
0.99702
3
17
Before
placing DG
0.91367
After placing
DG
0.95005
0.99769
18
0.91306
0.94947
0.98295
0.98716
19
0.99650
0.99716
4
0.97547
0.98230
20
0.99292
0.99358
5
0.96807
0.97764
21
0.99221
0.99288
6
0.94967
0.96503
22
0.99158
0.99224
7
0.94618
0.96258
23
0.97938
0.98361
8
0.94134
0.96281
24
0.97271
0.97696
9
0.93507
0.96364
25
0.96938
0.97365
10
0.92925
0.96504
26
0.94774
0.96313
11
0.92839
0.96421
27
0.94517
0.96061
12
0.92689
0.96277
28
0.93373
0.94937
13
0.92074
0.95685
29
0.92552
0.94129
14
0.91848
0.95467
30
0.92196
0.93779
15
0.91706
0.95331
31
0.91780
0.93370
16
0.91570
0.95200
32
0.91688
0.93280
33
0.91660
0.93782
Table 3. Comparison of Active and Reactive power losses in 33-Busradial distribution system
DG placement
Active power losses
(KW)
Reactive power losses
(KVAR)
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.Sandhya, Dr.A.Jaya Laxmi and Dr.M.P.Soni
78
Before placing DG
202.70
135.23
After placing DG
25.29
3.34
Table 4. Bus ranking based up on the loss reduction capability for 33-Bus radial distribution system
Reactive
power
losses
(KVAR)
Real
power loss
reduction
(%)
Reactive
power loss
reduction
(%)
Pi  Pg  Pd
DG Size
(MVAR)
Real
power
losses
(KW)
1.1079
0.0991
132.29
88.40
34.6716
34.5815
1.0479
9
0.7461
0.0723
147.59
98.21
27.1160
27.3218
0.6861
16
0.6726
0.0680
147.71
98.21
27.0567
27.3218
0.6126
17
0.6502
0.0669
151.03
101.77
25.4172
24.6873
0.5902
15
0.5370
0.0615
153.62
101.80
24.1382
24.6651
0.4770
11
0.5390
0.0616
156.59
104.04
22.6716
23.0074
0.4940
30
0.5123
0.0605
159.61
107.14
21.1802
20.7133
0.3123
12
0.3007
0.0536
174.58
116.30
13.7876
13.9347
0.2407
8
0.2766
0.0531
181.86
121.09
10.1925
10.3899
0.0766
Bus
NO.
DG
Size
(MW)
10
(MW)
Fig.3 Bus Voltages Before and After Optimal DG Installation in the 33-Bus System
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.Sandhya, Dr.A.Jaya Laxmi and Dr.M.P.Soni
79
Fig. 4. Branch Currents Before and After Optimal DG Installation in the 33-Bus System
Fig. 5 Optimal Real Power Production Before and After Optimal DG Installation in the 33-Bus System
The voltages before and after optimal DG installation is
shown in Fig. 3, from which it is clear that voltage profile is
improved by optimal placement of DG. The branch currents
before and after DG placement is shown in Fig. 4 and from
this it is observed that the branch currents are decreases after
placing DG compared to before placing DG. The Fig. 5 shows
the optimal real power production before and after DG
placement. It is clearly observed that the optimal real power
loss is reduced after DG placement. From the results it can be
observed that the voltages obtained from after placing DG is
greater than before placing DG and the active power losses
reduced from 225.02 to 129.46 KW which results in 42.4673
% real power loss reduction and the reactive power losses
reduced from 102.18 to 61.34 KVAr which results in 39.9686
% reactive power loss reduction and minimum voltage is
increased to 0.94326 from 0.90918 (p.u).
V. CONCLUSION
This paper presents methodology to place wind turbine DG
optimally in primary distribution systems with the view of
minimizing the real power loss in the system while
considering its characteristic. The methodology is fast and
accurate in determining the size and location of DG. In this
paper, it is assumed that the DG installed at one location at a
time, which is a valid assumption. It is observed that the
optimal DG placement in the radial distribution system
improves the voltage profile. Losses of the system are also
reduced with a good percentage, after placing DG.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
K.Sandhya, Dr.A.Jaya Laxmi and Dr.M.P.Soni
REFERENCES
[1]. W.F. Tinnery and C.S.Hart, “Power flow solution by
Newton’s”, IEEE Transaction On power Apparatus and
Systems, Vol. PAS-86, Nov.1967, pp. 1449-1460.
[2]. B. Stott and O.Alsac, “Fast decoupled load flow”, IEEE Trans.
on power Apparatus and Systems, Vol. PAS-93, 1974, pp.
859-869.
[3]. S.I.Wamoto and Y.Tamura, “A load flow calculation method for
ill-conditioned pwer system”, IEEE Trans.on power Apparatus
and Systems, Vol. PAS-100, 1981, pp. 1736-1740.
[4]. D.Rajicic and Y. Tamura, “A modification to fast decoupled
power flow for networks with high R/X Ratio”, IEEE
Transaction on power systems, Vol. 3, 1988, pp. 341-348.
[5]. W.H.Kersting and D.L.Mendive, “An application of ladder
networks theory to the solution of three phase radial load flow
problem”, IEEE PES winter meeting New York, January 1976,
paperA76 044-8.
[6]. D. Shirmohammadi and H.W.Hong, “A compensation - based
power flow method for weakly meshed distribution and
transmission networks”, IEEE Trans. on power delivery, Vol. 3,
1988, pp.753-762.
[7]. Mithulananthan, N. Oo, T. and Phu, L.V. , “ Distributed
Generation Placement in Power Distribution System Using
Genetic Algorithm”, International Journal on Science, Vol. 9,
No. 3, pp. 55-62
[8]. Kim, K. H. Lee, Y. J. Rhee, S. B. Lee, S. K. and You, S. K.,
“Dispersed Generation Placement Using Fuzzy-GA in
Distribution System”, In Proceedings of IEEE Power
Engineering Society Summer Meeting, Chicago, Vol. 3,2002,
pp. 1148-1153.
[9]. Kim, J. O. Nam, S.W. Park, S. K. and Singh, C., “ Dispersed
Generation Planning Using Improved Hereford Ranch
Algorithm”, Electric Power Systems Research, Vol. 47,1998,
pp. 47-55.
80
of Technical Education (M.I.S.T.E), Member System Society of India
(M.S.S.I), Member IEEE, Member International Accredition Organization
(IAO) and also Member of Institution of Electronics and Telecommunication
Engineers (MIETE).
Dr. M. P. Soni, Worked as Addl. General Manager
in BHEL (R & D in Transmission and power System
Protection. Worked as Senior Research Fellow at
I.I.T. Bombay for BARC Sponsored Project titled,
‘Nuclear Power Plant Control’ during the year 1974
- 1977. Presently Working as Professor and Head,
Department of Electrical and Electronics
Engineering, M.J. College of Engineering and
Technology, Banjarahills, Hyderabad. India. He has undertaken the following
projects like “Dynamic Simulation Studies on Power System and Power Plant
Equipments”, “Initiated developments in the area of Numerical Relays for
Substation Protection”, “Developed Microprocessor based Filter bank
protection for National HVDC Project and commissioned at 220 kV Substation
s ,MPEB Barsoor and APTRANSCO Lower Sileru, Terminal Stations of the
HVDC Project. “Commissioned Numerical Relays and Low cost SCADA
System at 132kV, GPX Main Distribution Substation, BHEL Bhopal”. He has
20 international and national conference papers to his credit. His research
interests include power System protection and advanced control systems.
K.Sandhya, obtained B.Tech degree in 2001 and
M.Tech in 2007 with specialization in Electrical
Power
Systems from Jawaharlal
Nehru
Technological University and pursuing Ph.D.
(Power Quality) from Jawaharlal Nehru
Technological University, Hyderabad, India. She
has 11 years of teaching experience. Her research
interests are Power Systems, Power Quality, FACTS
and Custom Power Devices. She has 6 international
and national conference papers to her credit. She is a
Member of Indian Society of Technical Education (M.I.S.T.E).
Dr. A. Jaya Laxmi completed her B.Tech. (EEE)
from Osmania University College of Engineering,
Hyderabad in 1991, M. Tech. (Power Systems) from
REC Warangal, Pradesh in 1996 and completed Ph.D.
(Power Quality),
from
Jawaharlal Nehru
Technological University College of Engineering,
Hyderabad
in 2007. She has five years of
Industrial experience and 14 years of teaching
experience. She has worked as Visiting Faculty at
Osmania
University College of
Engineering,
Hyderabad and is presently working as Associate Professor, Department of
Electrical and Electronics Engineering, JNTU College of Engineering,
Hyderabad. She has 50 International and 10 National papers published in
various conferences held at India and also abroad. She has 20international
journal papers and 5 national journals & magazines to her credit. Her research
interests are Neural Networks, Power Systems & Power Quality. She was
awarded “Best Technical Paper Award” for Electrical Engineering in Institution
of Electrical Engineers in the year 2006. Dr. A. Jaya Laxmi is a Member of
Institution of Electrical Engineers Calcutta (M.I.E), Member of Indian Society
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Ms. Preeti Dhiman, Deepankar Anand, Ekta Singh and Komal Grover
81
PC Based Speed Control of Induction Motor
Ms. Preeti Dhiman, Deepankar Anand, Ekta Singh and Komal Grover
Abstract—In industrial surroundings induction motors are
gaining popularity due to their performing proficiency. Mostly
hardware manual control system is used for controlling the
various parameters of induction motor such as speed, torque,
direction and frequency. In the present paper, we are
controlling the speed of an induction motor by controlling the
voltage required to drive the motor by using Thyristor. The
whole procedure for controlling the speed of an induction
motor is being done by coding in MATLAB. This method of
controlling speed of induction motor is advantageous as
compared to other conventional methods using techniques
which require wires for their proper implementation.
Keywords—MATLAB, optocoupler, HT12E(12-bit
encoder), HT12D(12-bit decoder), Microcontroller,
M9MZ60G4Y 4P 60 W 200 V / 220 V (induction
motor).
1. INTRODUCTION
A simplest method to control the rotation speed of an
Induction motor is to control its driving voltage. The higher
the voltage is, the higher speed the motor tries to reach. An
induction or asynchronous motor is a type of AC motor
where power is supplied to the rotor by means of
electromagnetic induction, rather than by slip rings and
commentators as in slip-ring AC motors. These motors are
widely used in industrial drives, particularly poly phase
induction motors, because they are robust, have no friction
caused by brushes, and their speed can be easily controlled.
Various other methods are also been used like fuzzy logic
approach which makes use of Simulink. Another method
called ANFIS (Adaptive Neuro-Fuzzy Inference System) is
also used in some approaches of speed control of induction
motor.
In this research paper we are going to introduce speed
control of induction motor. In this paper we are using
MATLAB to generate code for controlling induction motor
connected at the parallel port. At the pc parallel port we
have connected RF transmitter, to transmit code to the
remote location. At the remote location we have RF receiver
microcontroller and Induction motor. The microcontroller
receives decoded binary signal and performs programmed
logical operation on motor.
Ms. Preeti Dhiman is working as Asst. Prof. Galgotia’s College of Engg. &
Tech, Preetidhiman81@gmail.com, Ekta Singh, Deepankar Anand and
Komal Grover are with Galgotia’s College of Engg. & Tech, Emails:
Ektasingh2309@gmail.com,
Deepravilko0522@hotmail.com
,
Komalgrover89@gmail.com
2.
WORKING METHODOLOGY
In recent years, speed control of induction motor drive is
widely used in high performance drive system because of its
advantages like high efficiency, very simple , extremely
rugged, good power factor and it does not require starting
motor. Induction motors are used in many applications such
as HVAC, Industrial drives control, automotive control,
etc... In recent years there has been a great demand in
industry for adjustable speed drives [1].
Fuzzy logic control has found many applications in the
past decade. The simulation work in fuzzy logic controller is
to be done by varying the change of mutual inductance and
rotor resistance which in itself is a major problem. Fuzzy
Logic, deals with problems that have vagueness, uncertainty
and use membership functions with values varying between
0 and 1 [2]. This means that if a reliable expert knowledge is
not available or if the controlled system is too complex to
derive the required decision rules, development of a fuzzy
logic controller become time consuming and tedious or
sometimes impossible.
The advantage of coding in MATLAB is that it control
the speed of induction motor using low cost PC based
platform. The code generated will be sent to the parallel port
of PC from where it will be converted into digital form.
Pin
number
on
connector
1
I/O
Direction
Active
Polarity
Signal Description
Output
0
2-9
Output
-
10
Input
0
11
Input
0
12
Input
1
13
Input
1
14
Output
0
Strobe
(data
available signal).
Data lines (bit 0 is
pin 2, bit 7 is pin 9).
Acknowledge
line
(active when remote
system has taken
data).
Busy line (when
active,
remote
system is busy and
cannot accept data).
Out of paper (when
active, printer is out
of paper).
Select. When active,
printer is selected.
Auto feed. When
active, the printer
automatically inserts
a line feed after
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Ms. Preeti Dhiman, Deepankar Anand, Ekta Singh and Komal Grover
82
every carriage return
it receives.
15
Input
0
16
Output
0
17
Output
0
18-25
-
-
Error. When active,
there is a printer
error.
Init. When held
active for at least 50
µsec, this signal
causes the printer to
initialize itself.
Select input. This
signal,
when
inactive, forces the
printer off-line.
Signal ground.
Table 2.1: Parallel port signal
Table 2.1 shows pin details of the standard parallel port
(SPP) and their traditional usage. The base address of the
first parallel port (LPT1) is 378 (hex) or 888 (decimal). The
data port of the parallel port can be accessed at its base
address. The status port can be accessed at base address+ 1,
i.e., 0379 hex (or 889 decimal). The control port can be
accessed at base address+ 2, i.e., 037A hex (or 890 decimal).
In case you are using LPT2 port, then substitute the base
address of LPT2 as 0278 (hex) in place of 0378 (hex).
The circuit for interfacing the PC’s parallel port to the
devices to be controlled. The parallel port outputs the
control signals generated by the software. The control
signals are not continuous but a single clock pulse. For
every ‘on’ or ‘off’ control, only a single clock pulse is sent
from the parallel port to the circuit.
A.
1.
2.
3.
4.
5.
6.
7.
TRANSMITTER SECTION:
The transmitting site checks the busy line to see if the
receiving is busy. If the busy line is active, the
transmitter waits in a loop until the busy line becomes
inactive.
The transmitting site places its data on the data lines.
The transmitting site activates the strobe line.
The transmitting site waits in a loop for the
acknowledge line to become active.
The transmitting site sets the strobe inactive.
The transmitting site waits in a loop for the
acknowledge line to become inactive.
The transmitting site repeats steps one through six for
each byte it must transmit.
Figure 2.1 Transmitter section block diagram
There are many situations where signals data need to be
transferred from one subsystem to another within a piece of
electronics equipment, or from one piece of equipment to
another, without making a direct ohmic electrical connection.
Often this is because the source and destination are (or may
be at times) at very different voltage levels like a
microprocessor which is operating from 5V DC but being
used to control a triac which is switching 240V AC. In such
situations the link between the two must be an isolated one,
to protect the microprocessor from overvoltage damage.
Relays can of course provide this kind of isolation, but even
small relays tend to be fairly bulky compared with ICs and
many of today’s other miniature circuit components because
they are electro-mechanical, relays are also not as reliable
and only capable of relatively low speed operation. When
there is a need of small size, higher speed and greater
reliability, a much better alternative is to use an optocoupler.
These use a beam of light to transmit the signals or data
across an electrical barrier, and achieve excellent isolation.
Optocouplers typically come in a small 6-pin or 8-pin IC
package, but are essentially a combination of two distinct
devices: an optical transmitter, typically a gallium arsenide
LED (light-emitting diode) and an optical receiver such as a
phototransistor or light-triggered diac. The two are separated
by a transparent barrier which blocks any electrical current
flow between the two, but does allow the passage of light.
The basic idea is shown in Fig.1, along with the usual circuit
symbol. HT 12E (Encoder).
Figure 2.2: Optocoupler
The 212 encoders are a series of CMOS LSIs for remote
control system applications. They are capable of encoding
information which consists of N address bits and 12_N data
bits. Each address/ data input can be set to one of the two
logic states. The programmed addresses/data are transmitted
together with the header bits via an RF or an infrared
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Ms. Preeti Dhiman, Deepankar Anand, Ekta Singh and Komal Grover
83
transmission medium upon receipt of a trigger signal. The
capability to select a TE trigger on the HT12E or a DATA
Trigger on the HT12A further enhances the application
flexibility of the 212 series of encoders. The HT12A
additionally provides a 38 kHz carrier for infrared systems.
Figure 2.3: Block diagram of HT12E
A.
Figure 2.4: Block diagram of Receiver section
RECEIVER SECTION:
1. The receiving site sets the busy line inactive (assuming it
is ready to accept data)
2. The receiving site waits in a loop until the strobe line
becomes active.
3. The receiving site reads the data from the data lines (and
processes the data, if necessary).
4. The receiving site activates the acknowledge line.
5. The receiving site waits in a loop until the strobe line
goes inactive.
6. The receiving site sets the acknowledge line inactive.
7. The receiving site repeats steps one through six for each
additional byte it must receive.
B.
RF Receiver:
HT 12D Receive and decode 12 bit encoded data
transmitted by HT12E, for further processing. The HT12D is
12 bit decoders are a series of CMOS LSIs for remote control
system applications. They are paired with Holtek’s 2^12
series of encoders. For proper operation, a pair of
encoder/decoder with the same number of addresses and data
format should be chosen. The decoders receive serial
addresses and data from a programmed 2^12 series of
encoders that are transmitted by a carrier using an RF
transmission medium. They compare the serial input data
three times continuously with their local addresses. If no
error or unmatched codes are found, the input data codes are
decoded and then transferred to the output pins. The VT pin
also goes high to indicate a valid transmission. The 2^12
series of decoders are capable of decoding information that
consist of N bits of address and 12_N bits of data. Of this
series, the HT12D is arranged to provide 8 address bits and 4
data bits.
The decoded data is used to control the speed of
induction motor in various ways. Here we using pulse width
modulation technique with microcontroller logic [3], [4].
C.
MICROCONTROLLER LOGIC:
The function of microcontroller is to control input output
based on the programmed embedded hex logic. The
microcontroller continuously scans input logic. The input
logic is 4BCD data from HT12D one from fire sensor and
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Ms. Preeti Dhiman, Deepankar Anand, Ekta Singh and Komal Grover
one from light sensor. If any one of them changes their logic
level microcontroller goes to particular subroutine and
perform particular task.
Let us consider a case when key ‘2’ is pressed on the
keyboard of PC, thus at receiver side HT12D generate
corresponding BCD logic 0010. The microcontroller receives
0010 at pin no 1,2,3,4. The microcontroller is programmed if
input is 0010, move to motor left. The motor will move left.
This moment is done by microcontroller using pulse width
modulation. Thus when we press 2 key microcontroller
provide different pulses to the induction motor. In the same
way all microcontroller subroutine gets executed and perform
corresponding task.
2.
84
[3]
[4]
[5]
[6]
[7]
EASE OF USE
One of the problems with the ANFIS design is that a
large amount of training data might be required to develop an
accurate system, depending always on the research study.
Another disadvantage, which has been discussed, is the fact
that there is only one output from an ANFIS. Thus, ANFIS
can only be applied to prediction tasks or the approximation
of nonlinear function where there is only one output.
Furthermore, another drawback has to do with the
optimization algorithm used in this study. More specifically,
the error back-propagation algorithm is based on gradient
descent method which according to the error surface tries to
find the best weight and bias composition in order to
minimize the network error, but there are some disadvantages
like slow converges, lack of robustness and inefficiency[5-8].
[8]
S.M.Wenkhede, R.M.Holmukhe, Miss.A.M.Kada, Miss.P.R.
Shinde, P.S. Chaudhary, Micro controller Based Control of
Three
Phase
Induction
Motor
Using
PWM
Technique,International Conference on Electrical Energy and
Networks (ICEEN), 2011
Mrs.DeepaliS.Shirke, Prof. Mrs.Haripriya, H.Kulkarni,
Microcontroller based speed control of three phase induction
motor using v/f method,International Journal of Scientific and
Research Publications (IJSRP), ISSN2250-3153, volume
3,ISSUE 2, 2013 Electr
Industrial electronic series, Series Editor, J. David Irwin,
Auburn University
8051 Microcontroller M.A. Mazidi
Y. Yorozu, M. Hirano, K. Oka, and Y. Tagawa, Electron
spectroscopy studies on magneto-optical media and plastic
substrate interface, IEEE Transl. J. Magn. Japan, vol. 2, pp.
740–741, August 1987 [Digests 9th Annual Conf. Magnetics
Japan, p. 301, 1982].
M. Young, The Technical Writer's Handbook. Mill Valley,
CA: University Science, 1989.
In our approach, we are using thyristor to generate different
set of voltages for controlling the speed of an induction
motor and this is being achieved by controlling its firing
angle. So, out main focus is to control their speed of motor
using the easiest way.
3.
CONCLUSION
In this paper, we presented a system for speed control of
induction motor using easy n less tedious circuitry.
Microcontroller that has been used will make the control
more effective. Since induction motor is widely used in
industries, thus its speed control will be a great asset.
References
[1]
[2]
W. Leonhard, Control of Electrical Drives, Springer-Verlag
Berlin Heidelberg, New York, Tokyo, 1985.
T. D. Dongale1, T .G. Kulkarni, S.R.Jadhav, S.V.Kulkarni,
R. R. Mudholkar, Ac induction motor control-neurofuzzy,International Journal Of Engineering Science and
Advanced Technology(IJESAT),ISSN:2250-3676,Volume 2,
issue-4,2012
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Annapurna Birdar and Ravindra G. Patil
85
Energy Conservation Using Variable Frequency
Drive
Annapurna Birdar and Ravindra G. Patil
Abstract: The paper describes the use and importance of VFD
drive in firing of ceramic insulators. The ceramic insulators
undergo certain physical treatments before being subjected to
some mechanical and electrical test. Heat treatment is the most
important one. This treatment makes the insulator durable,
bonded and moisture less. The heating process is generally
carried out in kiln. It requires gas or oil as fuel and air as
medium.
Volume of air pumped into the kiln is controlled by air blower
motor, which is necessary for firing of insulators. Variable
frequency drives (VFDs) are used to control three phase
induction motor which intern controls the output of an air
blower motor. VFDs are used to vary supply frequency to
control the speed of air blower motor.
Installation of VFDs offers high efficiency ease of operation and
savings in cost due to less power consumption. VFDs require less
maintenance, improve process control and have become the
drive of choice in the majority of applications. In addition, speed
control is generally the most energy efficient flow control
technique because it requires the least amount of energy to meet
the given load.
The project is designed to highlight the use of VFDs for the
control of air flow in the kiln used for firing of insulators by
varying the supply frequency.
Keywords: Blower Control, Energy Conservation, Speed
Control, Supply Frequency Control, VFD.
I. INTRODUCTION
Motors are designed to run at a constant speed. However,
motor drive systems are often operated at variable load. In
particular, fans and pumps have highly irregular load profiles.
This means, the motors on these systems either run at constant
speed bypassing the excess capacity, or use some form of
capacity regulation such as dampers, valves or inlet guide
vanes, all of which are very inefficient. System output can be
controlled by adjusting the speed of the motor using Variable
Frequency Drives. VFDs offer higher efficiencies are easier to
control, require less maintenance, improve process control
and have become the drive of choice in the majority of
applications. In addition, speed control is generally the most
energy efficient flow controls technique because it requires
the least amount of energy to meet the given load.
II. INDUCTION MOTORS
Induction motors [3] are the most common motors used in the
industrial motion control systems as well as in main powered
home appliances. Although induction motors are easier in
design than DC motors, the speed and torque control in
various types of induction motors require a greater
understanding of the design and the characteristics of these
motors. Three phase induction motors are commonly used in
adjustable-speed drives. Their main advantages over other
motors are self-starting property, higher power factor, good
speed regulation and robust construction.
Working principle
The working principle of the three-phase induction motor is
based on the production of rotating magnetic field (RMF).
Such a field is produced by supplying currents to a set of
stationary windings, with the help of three phase ac supply.
The current carrying windings produce the magnetic field or
flux, due to the interaction of three fluxes produced due to
three phase supply, resultant flux has a constant magnitude
and its axis rotating in space, without physically rotating the
windings. The RMF gets cut by rotor conductors as RMF
sweeps over rotor conductors. As a result emf gets induced in
the rotor conductors called rotor induced emf. Any current
carrying conductor produces its own flux. Thus, the rotor
produces its flux called rotor flux. As all the rotor conductors
experience a force due to the interaction of the two fluxes, the
overall rotor experiences a torque and starts rotating. Thus,
interaction of the two fluxes is essential for motoring action.
Speed of an induction motor:
The magnetic field created in the stator rotates at a
synchronous speed (Ns), which is given by
=
120
Where, = the synchronous speed of the stator magnetic
field in RPM, P= the number of poles on the stator, f= the
supply frequency in hertz
Annapurna Birdar, M.Tech(PES), EEED, BEC, Bagalkot and Ravindra G.
Patil
Associate Professor,
EEED,
BEC,
Bagalkot, Emails:
biradar_annapurna@yahoo.co.in, rgpapril@yahoo.co.in
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Annapurna Birdar and Ravindra G. Patil
Figure 1: Operating principle of Induction motor
The magnetic field produced in the rotor because of the
induced voltage is alternating in nature. To reduce the relative
speed, with respect to the stator, the rotor starts rotating in the
same direction as that of the stator flux and tries to catch up
with the rotating flux. However, in practice, the rotor runs
slower than the stator field. This speed is called the Base
speed ( ). The difference between and is called the
slip. The slip varies with the load. An increase in load will
cause the rotor to slow down or increase slip. The slip is
expressed as a percentage and can be determined by the
following expression.
−
%
=
∗ 100
Speed control of ac induction motors:
Speed control of a motor is a provision for intentional change
of speed according to the requirement of workload connected
with the motor.
A three-phase induction motor is inherently a constant speed
motor and it is very difficult to achieve smooth speed control
and if speed control is achieved by some means, the
performance of the induction motor in terms of its power
factor, efficiency etc gets adversely affected.
The speed of the induction motor depends on the frequency (f)
and the number of poles. The synchronous speed can be
obtained by the following expression.
= (1 − ) ∗
Where, ‘Nr’ is the rotor speed and s is the slip which has an
operational range of 0.01 to 0.05.
Methods of Speed Control:
1.
Speed control by changing the rotor resistance
Torque produced in case of three-phase induction motor is
given by
=
∗ ∗
∗
+( ∗ )
Where,
= rotor induced emf per phase on standstill
condition
= rotor reactance per phase on standstill
= rotor resistance per phase on standstill
S= slip.
For low slip region ( ∗ ) ≪
and can be neglected and
for constant supply voltage
is also constant. Therefore,
torque is inversely proportional to rotor resistance. Thus if the
rotor resistance is increased, the torque produced decreases.
86
But when the load on the motor is same, motor has to supply
same torque as load demands. Thus, motor reacts by
increasing its slip to compensate decrease in T due to
and
maintains the load torque constant. So due to additional rotor
resistance , motor slip increases i.e. the speed of the motor
decreases. But this method has the following disadvantages:
 Large speed changes are not possible. This is
because, for large speed change, large resistance is
required to be introduced in rotor which causes large
rotor copper loss to reduce the efficiency.
 The method cannot be used for squirrel cage
induction motor.
 Speed above rated values cannot be obtained.
 Large power losses occur due to large losses and
reduced efficiency.
 Sufficient cooling arrangements are required, which
make the external rheostats bulky and expensive.
2.
Speed control by changing number of poles
In the pole changing method, the stator winding of each
phase is divided into two equal groups of coils. These coil
groups are connected in series or parallel with the current
direction being reversed only in one group to create two
different numbers of poles (even) in the ratio 2:1
respectively. When the connection is changed from series
to parallel or vice versa, the current in one of the group of
coils is also reversed at the same time. This technique is
called consequent pole method, which is applied to all the
three windings (phases). This type of speed control is
suitable for squirrel cage rotor which can adapt to any
number of stator poles. This method has the following
disadvantages:
 Smooth speed control is not possible.
 Two different stator windings are to be wound;
hence increases the cost of the motor.
 Complicated from design point of view.
3.
Speed control by changing stator voltage
The torque developed by an induction motor is
proportional to the square of the voltage applied. If the
supply voltage is reduced below rated value, torque also
reduces. To supply the same load it is necessary to
develop same torque hence the value of slip increases so
that torque produced remains the same. Increase in slip
means motor runs at a lower speed. This method of speed
control is suitable for a narrow band of speeds. Starting
currents of such motors is very high.
Also, the rotor must have high inherent resistance to limit
the inrush of the current. This in turn means that the
losses in the rotor will be very high since the power is
dissipated as heat. This results in overheating of the rotor.
This method is usually employed for slip ring induction
motor. This method has the following drawbacks:
 Due to the reduction in voltage, current drawn by the
motor increases and this may result in the
overheating of the motor.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Annapurna Birdar and Ravindra G. Patil


4.
Large change in voltages is required for small
change in speed.
Due to reduced voltage, rotor induced emf decreases
the value of maximum torque. Additional voltage
changing equipment is necessary.
Supply frequency control or V/f control
Since motor depends on the speed of the rotating
field, which depends on the supply frequency, speed
control can be affected by changing the frequency of
the AC power supplied to the motor.
As in most machines, the induction motor is
designed to work with the flux density just below the
saturation point over most of its operating range to
achieve optimum efficiency.
The flux density B is given by
Where V is the applied voltage, f is the supply frequency and
is a constant which depends on the stator winding constant
stator turns per phase. In other words, if the flux density is
constant, Volts per hertz is also a constant. This is an
important relationship and it has the following consequences.
For, speed control, the supply voltage must increase in step
with frequency; otherwise the flux in the machine will deviate
from the desired optimum operating point. Practical motor
controllers based on frequency control must therefore have a
means of simultaneous controlling the motor supply voltage.
This is known as Volts/Hertz control.
Increasing the frequency without increasing the voltage will
cause the reduction of the flux in the magnetic circuit thus
reducing the motor’s output torque. The reduced motor torque
will tend to increase the slip with respect to the new supply
frequency. This in turn causes a greater current flow in the
stator, increasing the IR volt drop across the winding as well
as
copper losses in the windings. The result is a major
drop in the motor efficiency. Increasing the frequency, still
further will ultimately cause the motor to stall.
Increasing the voltage without increasing the frequency will
cause the material in the magnetic circuit to saturate.
Excessive current will flow giving rise to high heat dissipation
due to
losses in the windings and high eddy current losses
in the magnetic circuit and ultimately damage to the motor
due to overheating. Increasing the voltage will not force the
motor to exceed the synchronous speed because as it
approaches the synchronous speed, the torque drops to zero.
Hence, in this method, the supply to the induction motor
required is variable voltage variable frequency supply and can
be achieved by electronic scheme using converter and inverter
scheme.
87
Figure 2: Electronic scheme for V/f control
The control system converts the desired speed to a frequency
reference input to a variable frequency, variable voltage
inverter. At the same time, it multiplies the frequency
reference by the Volts/Hertz characteristic ratio of the motor
to provide the corresponding voltage reference to the inverter.
Changing the speed reference will then cause the voltage and
frequency outputs from the inverter to change in unison.
III. VARIABLE FREQUENCY DRIVE
Brief Overview
Insulators are designed to work under variable atmospheric
conditions and are subjected to high mechanical stress. They
have to undergo certain physical treatments before they are
used in practical applications. One of the main treatments is
the heat treatment or firing. This process makes the insulator
lose its moisture content and makes it durable and bonded.
Insulators are heated at different pressures for different
periods of time. The heating of insulators is done inside the
kiln and air inside this heating chamber has to be maintained
under certain pressure so as to maintain the necessary
temperature. Air is used for combustion. The passage of air
inside the kiln is done by using air blower which is driven by
three phase induction motor. The amount of air sent into the
kiln by this blower is controlled by using damper
arrangement. The position of the damper is adjusted to let the
required amount of airflow into the kiln. But, this method of
controlling air pressure offers various disadvantages which
are dealt with in detail in later in this chapter. This
necessitated developing an efficient, economical, accurate
and flexible method for the heating of insulators.
The paper involves the basic study of a VFD, its use in
efficient firing of insulators, effective speed control method
of air blower motor and obtaining the cost saving analysis for
the same.
The VFD arrangement converts the supply as desired and
this converted supply is given to the motor. The speed of
rotation of the motor is controlled efficiently. [1]
Heat Treatment of Insulators
Figure 3: Block Diagram of treatment process
The parameters of the block diagram are explained below:
Fuel Tank: The fuel used in this kiln is gas. Huge cylinders
made of steel are used for storing the gas fuel. This is placed
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Annapurna Birdar and Ravindra G. Patil
in a remote place and the fuel is carried through steel pipes to
the required areas.
Fuel Pressure Control: The pressure of the incoming fuel
plays as important role in the prevailing temperature inside
the kiln. The pressure and the air to the kiln decide the
temperature inside the kiln. Dampers are used for the fuel
pressure control and they are witnessed by using manometers.
88
chambers within the cylinder which passage is opened and
closed by the movement of the piston and an air regulating
valve press-fit into the lower air port portion of the cylinder.
VFD System Description
A variable frequency drive system generally consists of an
AC motor, a controller and an operator interface. A general
block diagram of a VFD system is as shown in fig 4.
Burner: Gas is supplied to the kiln using burners made of heat
resistant materials. These burners are connected to the gas
supply pipes through valves. The figure shows one of the
burners in the kiln. A mixture of air and gas is sent inside the
heating chamber. There is an ignition spark plug called a
lighter which ignites the flame whenever required. The lighter
operation is controlled manually.
Gas Supply: The gas is supplied to the kiln by using burners
made of heat resistant materials. These
blowers are
connected to the gas supply pipes through valves.
The mixture of air and gas is sent inside the heating chamber.
Using igniting spark plug which is called a lighter ignites the
flame whenever required. The lighter operation is controlled
manually at the remote station as the lighter is electrical
igniter.
Kiln: The kiln is the heating chamber where the insulators are
treated. The kiln is build with bricks and they are coated with
heat resistive paints. Care is taken such that heat does not leak
out as this leakage not only reduces the efficiency of the
process but also affects the quality of the insulator.
Air Blower motor: Air blower controls the internal heat of the
chamber. This setup consists of a three phase induction motor
connected to a fan or blower. The pressure of air entering the
kiln is controlled by using damper of speed drive
arrangement. Separate pipes and tubes maintained for gas and
air.
Burning Process: Liquid petroleum gas (L.P.G.) is used as a
fuel in the burner. A small amount of fuel is passed through
pilot valve to the ignition chamber and at the same time a
voltage of about 5kV is applied across the spark plug through
the ignition transformer. If the fuel is ignited the ultra violet
(U.V.) sensor senses the blue flame and correspondingly a
feedback is sent to the main valve for the continued supply of
fuel. If the U.V. sensor doesn’t sense the blue flame a
feedback is sent to stop the further supply of fuel.
Air is supplied to the ignition chamber from primary and
secondary air panel through blowers. The primary air panel
supplies air necessary for burning and secondary air panel
helps in the uniform distribution of air throughout the
chamber.
Blowers work on the principle of centrifugal force. The
amount of air flow into the blower is controlled by variable
frequency drive (V.F.D’s).
Dampers: An air damper comprises a cylinder having air
ports at its upper and lower portions, a piston rod, a piston
movably mounted on one end of the piston rod, a return
spring, an air passage provided between upper and lower
Figure 4: Variable frequency drive system
VFD Motor
The motor used in a VFD system is usually a three-phase
induction motor .Some types of single-phase motors can be
used, but three-phase motors are usually preferred. Various
types of synchronous motors offer advantages in some
situations, but induction motors are suitable for most purposes
and are generally the most economical choice. Motors that are
designed for fixed-speed mains voltage operation are often
used, but certain enhancement to the standard motor designs
offer higher reliability and better VFD performance.
VFD Operation
When a VFD starts a motor, it initially applies a low
frequency and voltage to the motor. The starting frequency is
typically 2Hz or less. Starting at such low frequency avoids
the high inrush current that occurs when a motor is started by
simple applying the utility (mains) voltage by turning on a
switch. When a VFD starts, the applied frequency and voltage
are increased at a controlled rate or ramped up to accelerate
the load without drawing excessive current. This starting
method typically allows a motor to develop 150% of its rated
current. When a motor is simply switched on at full voltage, it
initially draws at least 300% of its rated current while
producing less than 50% of its rated torque. As the load
accelerates, the available torque usually drops a little and then
rises to a peak while the current remains very high until the
motor approaches full speed. A VFD can be adjusted to
produce a steady 150% starting torque from standstill right up
to full speed while drawing only 150% current.
With a VFD, the stopping sequence is just the opposite as the
starting sequence. The frequency and voltage applied to the
motor are ramped down at a controlled rate. When the
frequency approaches zero, the motor is shut off. A small
amount of braking torque is available to help decelerate the
load a little faster than it would stop if the motor were simply
switched off and allowed to coast. Additional braking torque
can be obtained by adding a braking circuit to dissipate the
braking energy or return it to the power source.
Functional Block Diagram
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Annapurna Birdar and Ravindra G. Patil
89
As already mentioned in the VFD operation the conversion
process incorporates three functions:


Rectifier Stage: A full-wave, solid-state rectifier
converts three-phase 50Hz power from a standard
440 or higher utility supply to either fix or adjustable
DC voltage. The system may include transforms if
higher supply voltage is used.
Inverter
Stage:
Electronic
switches-power
transistors or thyristors- switches the rectified DC on
and off, and produce a current or voltage waveform
at the design of the inverter and filter.
Control System: An electronic circuit receives
feedback information from the driven motor and
adjusts the output voltage or frequency to the
selected values. Usually the output voltage is
regulated to produce a constant ratio of voltage to
frequency (V/Hz). Calculation may incorporate
many complex control functions.
Table 1: The heating cycle of hollow insulators
Hours
Burner Temperature
175.83
274
413.2
16-20
554.4
21-25
735.6
26-30
871.6
31-35
912.4
36-40
975.4
41-45
1027.8
46-50
1035.2
51-55
1100.2
56-60
1109.4
1209.8
76-80
1259.0
Temperature
Table 2: The readings obtained for power consumption during the
heating cycle of hollow insulators with the damper system
IV. ENERGY SAVING ANALYSIS
6-10
71-75
Figure 6: The Temperature Required for Firing at Different Time
Periods
Observations
Heating Cycle:
Consider the below mentioned temperature table 1which
gives data for firing of insulators at different time
Periods.
11-15
1181.4
5 15 25 35 45 55 65 75
Advantages of VFD [5]
1. Bearing and winding life increases.
2. Smooth control of temperature, pressure and speed.
3. Maintenance and break down time decreases
1-5
1120.2
66-70
1400
1200
1000
800
600
400
200
0
Figure 5: Circuit Diagram of Variable Frequency Drive

61-65
Flow rate
(
/hr)
Hours
300
350
400
625
800
825
860
875
725
850
900
770
330
360
400
500
600
850
900
950
1060
1775
Total
19
2
14
2
2
2
2
2
2
5
2
2
2
2
2
2
2
2
3
2
2
2
77
With damper
KW
KWh
11.3
11.4
11.9
11.9
12
12.5
12.6
12.6
12.5
12.5
13.2
12
12
12.3
11.6
11.6
11.4
11.9
12.6
12.7
13.3
14.4
215.1
22.8
166.2
23.8
24
25
25.2
25.2
25
62.5
26.4
24
24
24.6
23.2
23.2
22.8
23.8
37.8
25.4
26.6
28.8
925.38
Table 3: The readings obtained for power consumption during the
heating cycle of hollow insulators after installation of VFD
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Annapurna Birdar and Ravindra G. Patil
Flow
rate
(m3/hr)
Hours
300
90
will be quite large. Thus for the best energy conservation, the
Variable Frequency Drives can be used.
With VFD
Speed
Frequency
KW
KWh
19
840
14
4.14
78.8
350
2
1080
18
4.41
8.8
400
625
800
14
2
2
1320
1340
1410
22
22.3
23.5
4.8
5.57
6.09
67.1
11.1
12.1
825
860
875
725
850
900
770
330
360
400
2
2
2
2
5
2
2
2
2
2
1490
1560
1620
1680
1740
1800
1830
1845
1920
2010
24.8
27.5
27
28
29
30
30.5
30.75
32
33.5
6.14
6.55
6.59
6.14
6.48
6.97
6.02
4.55
4.8
4.69
12.8
13.1
12.2
12.3
32.4
13.9
12
9.1
9.6
9.4
500
600
850
900
950
1060
1775
Total
2
2
2
3
2
2
2
77
1845
1845
1830
1860
1950
2000
2040
30.75
30.75
30.5
31
32.5
33.3
34
5.04
5.26
6.17
6.65
6.83
7.41
9.51
10.1
10.5
12.3
20
13.7
14.8
19
416.3
250
Cost paid per unit of energy consumed for commercial
purpose is Rs 6.25
 Total cost saving per annum: 27995*6.25 = 1.75
Lakh
 Cost of VFD : 1.5 Lakh
 Simple payback period : 1 year
Advantages of VFD System over Damper System
1. The method of firing the insulators became accurate
2. The temperature control of the firing chambers was
easily done with the help of AC drives
3. Loss of energy of the dampers while firing the
insulators was minimized
4. There was considerable increase in the production of
the insulators as the number of fault pieces is
minimized.
5. Increased efficiency
With Damper
200
KWH Consumed
Saving Calculation
As already mentioned, the employment of VFDs result in
considerable saving in energy for the industries and the
payback period of the invested amount into the VFD is also
very less. From the comparison of power consumption in
between damper technique and the VFD system of speed
control, the energy saving[1] per annum was calculated as
below:
 Energy consumed (in KWh) with damper: 925.3
KWh
 Energy consumed (in KWh) with VFD: 416.3 KWh
 Difference in KWh per cycle : 925.3 – 416.3= 509
KWh
 No. of cycles per year
: 55
 KWh saving per annum : 55*509=27995 KWh
With VFD
150
100
50
0
0
500
1000
1500
Flow rate
Figure 7: The Comparison of KWH Consumed When Damper and VFD
are Used
The above graph infers that with the use of VFD, which
controls the speed of air blower motor by varying the supply
frequency and voltage, the power consumed by motor can be
saved. As we know that the power consumed will be
proportional to the cube of the motor speed, the power saved
V. CONCLUSION
The declining resources combined with environmental global
warming concerns and increasing energy prices make energy
efficiency a crucial objective. Furthermore, improving energy
efficiency is often the cheapest, fastest and most
environmentally friendly way to meet the world’s energy
needs. [4]
The paper is designed to highlight the use of VFDs for the
control of air flow in the kiln used for firing of insulators by
varying the supply frequency.
Replacing the dampers by VFDs in the firing of insulators
gives more accurate firing and reduces the cost of production
of insulators. By the use of VFDs, loss of energy in damper
operation can be minimized and man power is reduced.
From the above estimation we can conclude that the
efficiency is increased and energy can be conserved
economically.
REFERENCES
[1] “Energy Conservation through the use of Variable Frequency
Drive”-A Case Study at Tata Power Company Ltd, Mumbai,
Pramod K. Sangale and Gaurav S. Tambe.
[2] Toshiba VF-P7 drive manual.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Annapurna Birdar and Ravindra G. Patil
91
[3] “Standard Handbook for Electrical Engineers”, Fink and Beaty,
11th edition, McGrawHillpublications.
[4] M. Benhaddadi, F. Landry, R. Houde, and G. Olivier, “Energy
Efficiency Electric Premium Motor-Driven Systems”,
978-1-4673-1301-8/12/$31.00 ©2012 IEEE, International
Symposium on Power Electronics, Electrical Drives,
Automation and Motion
[5] M.Veera Chary, N.Sreenivasulu, K.Nageswar Rao, D.Saibabu,
“Energy Saving Through VFD’s for Fan Drives in Tobacco
Threshing Plants”, 0-7803-5812-0/00/$10.00 ©2000 IEEE.
Annapurna Biradar was born in Bijapur,
Karnataka, India on 16 December 1988. She
obtained B.E (Electrical and Electronics) from
Visvesvaraya
Technological
University,
Karnataka., India. She is currently perusing
M.Tech Degree in Power and Energy Systems
in Electrical and Electronics Engineering, Basaveshwar Engineering
College, Bagalkot, India.
Ravindra G Patil was born in Hampiholi of
Ramdurg Tal, Karnataka, India on 1st April
1961. He obtained B.E (Electrical and
Electronics) from Karnataka University,
Dharwad, Karnataka India in 1984 and M.E
from Jadhavpur University, Kolkata, West
Bengal, India in 1993. His areas of interest
include Power Electronics, Machines and Drives. Presently he is
working as Associate Professor in the Department of Electrical &
Electronics Engineering at Basaveshwar Engineering College,
Bagalkot, India.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mrs. Hiral Raval Jani
92
Review Paper on Industrial Automation based
on OpenCV
Mrs. Hiral Raval Jani
Abstract: As the name Industrial Automation based on
OpenCV suggests that some kind of control in
instruments/industrial
machines
is
being
done.
OpenCV(Open Computer Vision) is the image processing
library. We can write programs in any IDEs(Integrated
Development Environments) in C/C++ language installing
OpenCV library in it. Based on that image processing results
we can control or automate industrial machines or any
process in industries. We can choose any sequences for that.
Keywords: Automation, IDE, Image Processing,
Linux, OpenCV
I.INTRODUCTION
Fig.2. Block Diagram to implement in Windows O.S.
Fig.1. Simple Block Diagram
Here is the simple block diagram. First block
shows any machine of industry. I have shown some
industrial examples below. For data acquisition we can
use any type of camera but for real time application USB
webcam is the best where very high resolution is not much
concern. For Image Analysis I have used Qt Creator IDE
in Linux Ubuntu. After that we can install and include
OpenCV library in Qt Creator. As a part of controlling
action we can display message/ make alarm on for
different kind of sequences. Then one can take actions
manually. Another possibility is, halt in process by
connecting hardware with Qt Creator. If we use Qt
Creator in Windows Operating System, we can use
proximity switch& PLC, and can give signal to stop
machine in case of error. Block diagram of it given below.
II.AUTOMATION
Automation involves the monitoring of inputs
and providing of outputs using the brain for processing the
inputs and making the decision in achieving what is
needed as an output. Automation gives more productivity,
safety, improved plant performance.
III.IMAGE PROCESSING
Fig.3. Image Processing Understanding
Mrs. Hiral Raval Jani is pursuing M.Tech I.C. 2013, D.D.I.T.,
Nadiad, Gujarat, India, Email: hir.hr.raval@gmail.com
IV.EMBEDDED/ MACHINE VISION
Embedded Vision refers to machines that
understand their environment through visual means.
Embedded vision is the merging of two technologies:
embedded systems and computer vision (also sometimes
referred to as machine vision). Computer vision is the use
of digital processing and intelligent algorithms to interpret
meaning from images or video. Computer vision has
mainly been a field of academic research over the past
several decades.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mrs. Hiral Raval Jani
93
V.OPENCV
OpenCV is an open source computer vision
library developed in C and C++. It is optimized and
intended for real-time applications. It is independent of
platforms and hardware, allows for generic loading,
saving and acquisition of images and videos, and provides
both low and high level APIs (Application Programming
Interfaces).
VI.LINUX
Linux was originally developed as a free
operating system for Intel x86-based personal computers.
It has since been ported to more computer hardware
platforms than any other operating system. It is a leading
operating system on servers and other big iron systems
such as mainframe computers and supercomputers: more
than 90% of today's 500 fastest supercomputers run some
variant of Linux. Linux also runs on embedded systems
such as mobile phones, tablet computers, network routers,
televisions and video game consoles; the Android system
in wide use on mobile devices is built on the Linux kernel.
Fig.5. Qt Creator
Qt Designer is used to design the User Interfaces
of your application. Even the Designer is integrated into
Qt Creator.
VII.UBUNTU
Ubuntu is a computer operating system based on
the Debian Linux distribution and distributed as free and
open source software, using its own desktop environment.
As of 2012, according to online surveys, Ubuntu is the
most popular Linux distribution on desktop/laptop
personal computers, and most Ubuntu coverage focuses
on its use in that market. However, it is also popular on
servers and for cloud computing.
VIII.QT
Fig.4. Qt Cycle
Qt is a framework to create cross-platform
applications. Using Qt one can create amazing GUI
applications quickly and easily. Visual Studio and X code
is used to create applications in Windows and Mac
respectively. Qt is similar to these tools in that it helps you
to design and code your application. But, the real
advantage of Qt is that that your application can be made
to run on Windows, Mac and Linux without you having to
change your code.
Qt Creator is the main IDE (Integrated
Development Environment).
Fig.6. Qt Designer
Qt Linguist is a tool for aiding the translation of
your application into various languages.
Fig.7. Qt Linguist
Qt Assistant is used for viewing the help files and
documentation related to Qt.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Fig.8. Qt Assistant
Using if conditions we can display message or
Vol. 2, Issue. 1, April-2013.
Mrs. Hiral Raval Jani
94
play sound if error occurred.
For sound we can use:
Qsound :: play(“file loacation.wav ”);
Before that we need to install and add various libraries
regarding sound in Qt Creator.
a.
IX.EXAMPLES
CNC lathe auto loader
Here we can continuously detect object and can say if
object is present or absent.
Fig.11 (b). Plastic Injection molding machine open with
pieces eject in clamp unit
b.
CNC router
Fig.9. CNC lathe with auto loader
Fig.11 (c). Plastic Injection molding machine closed
c.
Fig.10. CNC Router
We can show edges of work piece and calculate angle in
accordance with x, y positions.
Plastic Injection Molding Machine
Monitoring of pieces in molding machine can be done by
continuous tracking.
Fig.12 (a). Another Plastic Injection molding machine
open with pieces showing reference and template
Fig.12 (b). Plastic Injection molding machine open with
pieces showing result
Fig.11 (a). Plastic Injection molding machine open with
pieces
X.CONCLUSION
These are only examples. Image Processing is very
vast so we can use it on multiple machines and in multiple
ways. I have opted Linux Operating System, Qt Creator,
OpenCV even though other software like MATLAB,
LabView are available, as software cost matters.
Implementing Embedded Vision is challenging as there is
limited experience in building practical solutions.
Generally image processing based companies are from
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mrs. Hiral Raval Jani
95
abroad, if we are successful in such kind of applications, it
will be more beneficial. This is futuristic technique. It will
going to be deployed much, like the way wireless
technologies are now taking place.
ACKNOWLEDGMENT
I would like to thank you for the valuable
guidance of my Internal Guide Prof. S.S.Bhavsar and
External Guide Er. Mahesh Vyas.
[1]
REFERENCES
An Introduction to the Linux Command Shell For
Beginners by Victor Gedris In Co-Operation With The
Ottawa Canada Linux Users Group an ExitCertified
[2] Basic Linux Commands by Srihari Kalgi, M.Tech, CSE
(KReSIT), IIT Bombay May 5, 2009
[3] Open Source Computer Vision Library Reference Manual
Copyright © 1999 -2001 Intel Corporation All Rights
Reserved Issued in U.S.A.
[4] OpenCV Reference Manual v2.1, March 18, 2010
[5] Qt Tools Overview by Thomas Strehl 29.10.2009
[6] Getting
started
with
Qt
(http://qt.nokia.com/developer/getting-started/gettingstarted)
[7] Get started with Qt GUI Programming By Suvish V.T.
[8] Lectures on Image Processing, by Alan Peters. Vanderbilt
University. Updated 15 September 2011.
[9] Fundamentals of Embedded Computer Vision: Creating
Machines That See by Eric Gregori Senior Software
Engineer/Embedded Vision Specialist, BDTI, September
13, 2012
[10] Wikipedia
[11] Electronics for you, august 2012
[12] Webinar on www.designnews.com
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Manish Raval and Ved Vyas Dwivedi
96
Commencing the FACTS in Variable Energy
Sources Network to Optimize Existing
Transmission System with Stability
Manish Raval and Ved Vyas Dwivedi
Abstract: Growing concern for the environmental degradation
has led to the world’s interest in renewable energy resources.
Due to the beneficiary policy, variable wind, solar and hydro
generation is gradually increased in the world. The big mass of
variable generation is creating fluctuation in voltage, frequency
and power factor of grid network and it led to the instability in
the existing grid system of utility and also create the power
evacuation problem. To compensate the above problems the
grid networks requires a careful design to maintain the system
with continuous power flow operation without any limitations
as well as optimization of existing transmission system. The
focus of this research paper is to commence the FACTS
(Flexible A.C. Transmission System) to control the power flow
of the unbalanced transmission network due to impose of
power from variable generating system. This project proposes a
case study to control the power flow of power system with
UPFC. In this study 5-Bus network system has selected and
simulation has done with and without the UPFC to measure the
power flow of the network. With the use of UPFC the power of
overloaded transmission network regulated with good voltage
profile and avoids the evacuation problem. This system is
costlier and complex as compare to static voltage regulating
system.
Indexing words: Grid, Unified power flow controller, Load flow,
Voltage Regulation
1.
INTRODUCTION:
Grid connectively and transmission constants have often
been cited as key constants in wind energy development in
the country if the target of the National action plan on
climate change of achieving 15 percent power generation
through renewable energy sources by 2020 is to be met the
country needs to add 25000 MW of wind power capacity.
Though the Government has put in place the required policy
support to attract and encourage investor, unless issues
related to grid integration of wind power are sorted out this
target will remain more wishful linking. At present, potential
sites across the country remain undeveloped as evacuation of
power is technically not feasible due to saturation of the
local transmission system. Grid saturation has also resulted
in the loss of several MUs of power from existing wind
farms as grid managers impose back down instructions every
time power intake from other sources increases. Grid
managers instead of balancing the different elements
(including wind) in the increasingly complex national grids,
real wind as a risk to grid security. Erratic grid availability
has become a bigger cause for concern for developers in
recent times, especially because of the newly introduced
generation-based incentives and renewable energy
certificates. The benefits from which are entirely dependent
on the power feel in to the grid.
Connectivity challenges for new farms:Evacuation of power is one of the basic investment
decision criteria for wind power developers as the majority
of high wind potential sites are located in remote areas.
These areas, which have the potential for setting up large
wind projects of 100-200MW, usually have low
transmission capacity of about 20 MW. It is because of this
scenario that developers face what Jami Hossain, Chief
Member and Co-founder wind farm management services
calls “chicken and eggs: situation while planning large wind
farms for example, a given site may have excellent wind
potential but may have poor grid infrastructure, investments
in planning and land procurement risky.
Wind energy developers are also at a disadvantage when
it comes to bearing the construction cost of evacuation
infrastructure. Unlike conventional energy projects where
the cost is usually born by the transmission or distribution
companies.
Manish Raval is a 1Ph.D Scholar (Electrical Engg.), Department of
Engineering, Pacific University, Udaipur, Rajasthan-INDIA, E-mail:
manishraval_aei@yahoo.co.in, and Ved Vyas Dwivedi is Director, Noble
Group of Institutions – Junagadh, Gujarat – INDIA, Tel: +91-2691 030521;
Fax: +91-2691 034520; E-mail: director.principal.ngi@gmail.com
The Mandavising author of article in renewable source
[1] mentioned that the intermittent nature of wind power,
Solar power and hydro power (variable source) are major
cause for concern for grid managers as it leads to a low and
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Manish Raval and Ved Vyas Dwivedi
unpredictable plant load factor, which upsets the voltage
profile of the grid and also discussed about the evacuation
problems for wind energy and solar energy development in
India. The technology of power system utilities around the
world has rapidly evolved with considerable changes in the
technology along with improvements in power system
structures and operation.
At the same time building of the new transmission
circuits is becoming more difficult because of economic and
environmental reasons and Wright of Way problems.
Therefore, power utilities are forced to utilize existing
system without spending extra expenditure. However,
stability has to be maintained at all times. Hence, in order to
operate power system effectively, without reduction in the
system security and quality of supply, even in the case of
contingency conditions such as loss of transmission lines
and/or generating units, a new control strategies need to be
implemented.
In present day highly complex and interconnected power
systems, need to improve electric power utilization with
maintaining reliability and security. Available power
generation, usually not situated near a growing load center,
is subject to maintain economical and environmental and
power evacuation issues. In order to meet the increasing
power demand, utilities prefer to rely on already existing
generation and power transferring arrangements instead of
building new transmission lines that are subject to
environmental and economic issues. [1].
On the other hand, power flows in some of the
transmission lines are below their thermal limits, while some
lines are overloaded, which has as an overall negative effect
on voltage profiles and decreasing system stability and
security. In addition, existing traditional transmission
facilities, in most cases, are not designed to handle the
control requirements of complex, highly interconnected
power systems. This overall situation requires the review of
traditional transmission methods and practices, and the
creation of new concepts which would allow the use of
existing generation and transmission lines up to their full
capabilities without reduction in system stability and
security. Another reason that is forcing there view of
traditional transmission methods is the tendency of modern
power systems to follow the changes in today's global
economy that are leading to deregulation of electrical power
markets in order to stimulate competition between utilities
[1].
Commencement of Flexible A.C. transmission system
creates a tremendous quality impact on power system
stability. These features become even more significant
knowing that the UPFC can allow loading of the
transmission lines close to their thermal limits, forcing the
power to flow through the desired paths. This will give the
power system operators much needed flexibility in order to
satisfy the demands that will impose the deregulated power
system.
97
This project proposes a case study to control the power
flow of a power system with UPFC. In this study, a 5-Bus
network for the analysis with and without the UPFC has
been studied and presented.
Literature Survey
Many articles, journals and IEEE papers are found for
UPFC operation, modeling and control.
The UPFC which was proposed by [2], outlines the
technical and economic factors which characterize the
uniform, all solid-state power-flow controller approach for
real-time controlled, flexible AC transmission systems. The
unified power-flow controller in its general form can provide
simultaneous, real-time control of all basic power system
parameters (transmission voltage, impedance, and phase
angle), or any combinations thereof, determining the
transmitted power.
The [3] had proposed the Unified Power Flow Controller
(UPFC) for controlling power flow in modern power
systems. Essentially, the performance depends on proper
control setting achievable through a power flow analysis
program. This paper aims to present a reliable method to
meet the requirements by developing a Newton-Raphson
based load flow calculation program through which control
setting of UPFC can be determined directly.
The [4-5] presented their research work with digital
simulation of 14-bus power system using UPFC to improve
the power quality. The UPFC is also capable of improving
transient stability in a power system. It is the most complex
power electronics system for controlling the power flow in
an electrical power system.
The [6] simulated IEEE 5- bus system using MATLAB
Simulink to do the load flow analysis of the system. In this
paper the author shows that with use of UPFC the power
transfer capability of the same system can improve. While
the [7]shows that shunt FACTS devices plays a very
important role in controlling the reactive power flow when
placed at the midpoint of a long transmission line. It also
affects the system voltage regulation and transient stability
of the system. Author also analyzed when transient fault
occurs in the system FACTS devices connected to the
system becomes important part for transient stability.
2. Flexible A.C. Transmission
Alternating current transmission system incorporating
power electronic-based and other static controllers to
enhance controllability and increase power transfer
capability.
Flexibility of Electric Power Transmission: The ability to
accommodate changes in the electric transmission system or
operating conditions while maintaining sufficient steadystate and transient margins [8].
FACTS Controller: FACTS controller are the power
electronic-based system and other static equipment that
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Manish Raval and Ved Vyas Dwivedi
provide control of one or more AC transmission system
parameters.
The controllers that are designed based on the concept of
FACTS technology to improve the power flow control;
stability and reliability are known as FACTS controllers.
These controllers were introduced depending on the type of
power system problems. Some of these controllers were
capable of addressing multiple problems in a power system
but some are limited to solve for a particular problem. All
these controllers grouped together as a family of FACTS
controllers categorized as follows as shown in figure1.
 First Generation of FACTS Controllers: Static VAR
Compensator (SVC) and Thyristor Controlled Series
Compensator (TCSC)
 Second Generation of FACTS Controllers: Static
Synchronous Series Compensator (SSSC) and Static
Synchronous Compensator (STATCOM)
 Third Generation of FACTS Controllers. The third
generation of FACTS controllers is designed by
combining the features of previous generation’s series
and shunt compensation FACTS controllers. : Unified
Power Flow Controller (UPFC) and Interline Power
Flow Controller (IPFC) are third generation FACT
Controllers. They are discussed as below.
98
voltage magnitude and phase angle in series with the line to
control the active and reactive power flows on the
transmission line. Hence the series converter will exchange
active
and
reactive
power
with
the
line.
Fig.2 Unified Power Flow Controller (UPFC) [8].
Characteristic of UPFC:
The concept of UPFC makes it possible to handle
practically all the power flow control and transmission lines
compensation problems using solid-state controllers that
provide functional flexibility which are generally not
obtained by Thyristor-controlled controllers.
Interline Power Flow Controller (IPFC):
Its design is based on Convertible Static Compensator
(CSC) of FACTS Controllers. As shown in Figure 3, IPFC
consists of two series connected converters with two
transmission lines. It is a device that provides a
comprehensive power flow control for a multi-line
transmission system and consists of multiple number of DC
to AC converters, each providing a series compensation for a
different transmission line. The converters are linked
together to their DC terminals and connected to the AC
systems through their series coupling transformers. With this
arrangement, it provides series reactive compensation in
addition any converter can be controlled to supply active
power to the common dc link from its own transmission line
[9].
Fig.1 Block Diagram of FACTS Controllers [8].
Unified Power Flow Controller (UPFC):
It is designed by combining the series compensator
(SSSC) and shunt compensator (STATCOM) coupled with a
common DC capacitor. It provides the ability to
simultaneously control all the transmission parameters of
power systems, i.e. voltage, impedance and phase angle.As
shown in Figure 2. it consists of two converters – one
connected in series with the transmission line through a
series inserted transformer and the other one connected in
shunt with the transmission line through a shunt transformer.
The DC terminal of the two converters is connected together
with a DC capacitor. The series converter control to inject
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Manish Raval and Ved Vyas Dwivedi
Fig. 3 Interline Power Flow Controller [9]
99
Characteristics of IPFC:
To avoid the control of power flow problem in one
system with synchronization of power in other system,
installation of IPFC with parallel inverter is required to meet
the active power demand.
The UPFC concept was proposed by Gyugyi in 1992 [2]
within the concept of using converter based FACTS
technology. It consists of two voltage source inverter
connected back to back through a common DC link, as
illustrated in fig 4. This arrangement function as an ideal AC
to AC power converter in which the real power can freely
flow in either direction between the AC sides of the two
inverters. The reactive power on the two AC sides of the
inverters can be controlled independently.
Advantages of FACTS controllers [8]
 Power Quality and Reliability:
Modern power industries demand for the high quality of
electricity in a reliable manner with no interruptions in
power supply including constant voltage and frequency.
The change in voltage drops, frequency variations or the
loss of supply can lead to interruptions with high
economic losses. Installation of FACTS device at the
distribution system without increasing the short circuit
current level considerably increases the reliability for the
consumer.
The series inverter (inverter 2) is connected to the
transmission line through a series (booster) transformer in a
manner similar to the SSSC. The shunt inverter is connected
to the system bus through an shunt (excitation) transformer
in same way as an Advanced Static VAR Compensator
(ASVC). Therefore, the UPFC can be considered as a multifunction controller which is capable of providing the
performance of one or two FACTS devices. Because of its
structure, the UPFC provides new dimensions of
controllability, which have not been achieved with other
FACTS controllers.
 Power system stability:
Instabilities in power system are created due to long
length of the transmission lines, interconnected grid,
changing system loads and line faults in the system.
These instabilities results in reduced transmission line
flows or even tripping of the transmission. FACTS
devices stabilize transmission systems with increased
transfer capability and reduced risk of transmission line
trips.
 Flexibility:
The construction of new transmission lines take several
years but the installation of FACTS controllers in a
power system requires only 12 to 18 months. It has the
flexibility for future upgrades and requires small land
area.
 Environmental Benefits:
Construction of new transmission line has negative
impact on the economical and environmental factors.
Installation of FACTS devices in the existing
transmission lines makes the system more economical by
reducing the need for additional transmission lines.
 Reduced maintenance cost:
Maintenance cost of FACTS controllers are less
compared to the installation of new transmission lines.
As the number of transmission line increases, probability
of fault occurring in a line also increases resulting in
system failure. By utilizing the FACTS controllers in a
transmission network, power system minimizes the
number of line faults thus reducing the maintenance cost.
UPFC Basic Principle and Operation Modes
The Unified Power Flow Controller (UPFC) is a multifunction controller which can play an important role in
solving various transmission systems problems.
Fig. 5 Schematic diagram of a UPFC system [9]
Principles of Operation [9]
SSSC part of the UPFC performs the main function of
the UPFC by injecting a voltage Vser in series with the
transmission line. The injected voltage can be controlled
with theoretically little restrictions/ that is, the phase angle
of Vser can be controlled independently of the line current
between 0 and 2 , and the magnitude is ranging from zero
to predefined maximum value. This maximum value is
determined by the VA rating of the UPFC series inverter.
In the transmission line current flows through the
injected voltage resulting in active and reactive exchange
between the series inverter and the AC system. The real
power measured at the inverter output is supplied or
absorbed by the DC link side. The reactive power is
generated or absorbed internally between phases connected
by the inverter switches. As the magnitude and phase angle
of the series inverter injected voltage is fully controllable, it
can be used to achieve different conventional compensation
e.g. voltage regulation, series compensation or phase angle
regulation.
Construction of the UPFC
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Manish Raval and Ved Vyas Dwivedi
Inverter 1 (the exciter) which is connected in shunt with
the AC system is used essentially to provide the active
power demand of the series inverter at the common DC link.
As inverter 1 is a voltage source (viewed from the system), it
can generate or absorb reactive power at the connection
point. Such reactive power is independent of both the
reactive power generated by the series inverter and the active
power through the DC link. Therefore, the shunt inverter can
fulfill the function of the ASVC in providing reactive power
compensation at the system bus bar and at the same time
performing an indirect DC voltage regulation within the
UPFC.
Modes of operation
Conventional power transmission systems employ shunt
compensation, series compensation and phase angle
regulation. The UPFC can fulfill all these functions and
thereby meet multiple control objectives by an appropriate
choice of the injected voltage magnitude and angle, as
illustrated in the diagram given in figure 6. Therefore, there
are different modes of operation for each of the inverters
comprising the UPFC depending on the available local
reference signals. The UPFC global controller needs to be
able to switch between these modes according to the system
requirements.
100
angle with reference to the voltage of the system bus at
which the UPFC is connected.
Voltage regulation mode
The series converter simply generates the voltage
vector Vser with the magnitude and phase angle requested by
the reference input as shown in fig.7. These operating modes
may be advantageous when a separate system optimization
control coordinates the operation of the UPFC and other
FACTS controller employed in transmission system.

Fig.7 UPFC working as a voltage regulator [11]
Phase angle regulation mode
The injected voltage vector Vseris controlled with
respect to the input bus voltage vector V1so that the output
bus voltage vector V2is phase shifted relative to V1by an
angle specified by the reference input as shown in figure 8.

Fig.8UPFC working as a phase angle regulator/shifter [11]
Fig. 6 UPFC modes of operation [9]
Series inverter Modes of operation
Operation of the series inverter is divided into different
modes with distinctive characteristics. These modes are
dependent on the reference signal used to derive the
magnitude and phase angle of the injected voltage. In power
systems the local reference signals normally available are
the line current and the system bus voltage. These two
signals are recommended by many power systems
researchers [10] to be the reference signals for UPFC control
variables.
System voltage as a reference
In these modes, the series inverter generates a voltage
vector, which is controlled in both magnitude and phase-
Line current as a reference
In these modes the injected voltage generated by the series
inverter is determined by the transmission line current.
Line resistive compensation
In this mode, the injected voltage is maintained to
be in-phase with the line current in order to compensate the
transmission line voltage drop. The key point of such a
compensation scheme is to keep the transmission system
X/R ratio within an acceptable range based on the line
voltage rating.


Line reactive compensation
Magnitude of the injected voltage vector Vser is controlled in
proportion to the magnitude of the line current I, so that the
series insertion emulates reactive impedance when viewed
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Manish Raval and Ved Vyas Dwivedi
101
from the line. The desired impedance is specified by
reference input and in general it may be complex impedance
with resistive components of either polarity. When the
injected voltage is kept in quadrature with respect to the line,
current to emulate purely reactive (capacitive or inductive)
compensation. This operating mode matches with series
compensation in the system like SSSC and TCSC.
for the series inverter. This mode of operation is quoted as
“Bus Voltage Control Mode.
Power flow mode
The unified power flow control approach (series inverter)
can be broadening the basic power transmission concepts. It
is possible to implement the individual compensation
scheme discussed above but also a combine or real time
transition from one mode of operation to another and in
order to handle particular system contingencies, more
effectively than the other single function FACTS controllers.
Fig.10 Shunt Inverter in "Voltage Control Mode" [11]
In theory, the UPFC may be used to maintain a
prescribed and independently controllable real and reactive
power flow in a certain transmission corridor. In this case,
the injected voltage Vser is stipulated to have no phase angle
restriction and its magnitude is variable between zero and a
maximum permissible value. In practice, the UPFC may be
used to maintain or vary the active and reactive power flow
in a transmission system within a specific margin. The
operating point can be anywhere inside a circle with a radius
|Vsermax|, as shown in figure 9. The particular, but more
general, mode of operation has been chosen in this work to
analyze the capabilities of the UPFC to control the system
power flow.
The quadrature component is responsible for the
exchange of reactive power with the AC system. This in turn
supports the reactive power in the transmission system
irrespective of the variation of the bus voltage.
Shunt inverter current as a reference
When the current is used as a reference signal, the
inverter output voltage may be divided into two
perpendicular components. The in-phase component will
allow the shunt inverter to exchange real power with the DC
link and provide for the power losses.

(3) Simulation And Results of Test Case, 5-Bus System
Here for simulation work IEEE 5-bus system is chosen. In
this the UPFC is connected at bus 3. The simulation is done
for load flow analysis for without / with UPFC connected to
Fig. 9 UPFC in the power flow mode [11]
Shunt inverter modes of operation
The shunt inverter is operated to absorb or generate
certain amount of reactive power from/to the AC system. In
addition, it provides the real power demand of the series
inverter and power losses. Similar to the series, the shunt
inverter modes of operation are dependent on the reference
signal used to derive the magnitude and angle of the inverter
output voltage.
System bus voltage as a reference
The inverter output (Vsh) may be split into two
components (Vpand Vq) with respect to the AC system bus
voltage (V1) at which the UPFC is connected, as shown in
fig. 10. The in-phase component may be used to control the
system bus voltage in order to immune the controlled
transmission line from the changes within the rest of the
network.

system.
Fig 11 One line diagram of 500/230 kV Transmission
System [12]
A UPFC is used to control the power flow in a 500 KV
/230 KV transmission systems. The system, connected in a
loop configuration, consists essentially of five buses (B1 to
B5) interconnected through three transmission lines (L1, L2,
L3) and two 500 kV/230 kV transformer banks Tr1 and Tr2.
Two power plants located on the 230KV system generate a
total of 1500 MW which is transmitted to a 500 KV, 15000
MVA equivalent and to a 200 MW load connected at bus B3
as shown in fig.11.
The quadrature component allows the shunt inverter to
exchange real power with the AC system which is required
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Manish Raval and Ved Vyas Dwivedi
102
Simulation for without UPFC system
Fig. 13 Simulation with UPFC
Fig. 12. Simulation without UPFC [12]
As shown in figure 12, in the normal operation, most of
the 1200 MW generation capacity of power plant 2 is
exported to the 500 KV equivalents through 800 MVA
transformer connected between buses B4 and B5. The load
flow shows that most of the power generated by plant 2 is
transmitted through the 800 MVA transformer bank (925
MW out of 1000 MW). Transformer Tr-2 is therefore
overloaded by 125 MVA. This will now illustrate how a
UPFC can relieve this power congestion.
As shown in figure13, the UPFC located at the right end
of line L2 is used to control the active and reactive powers at
the 500 KV bus B3, as well as the voltage at bus B_UPFC.
The UPFC consists of two 100 MVA, IGBT-based,
converters (one shunt converter and one series converter
interconnected through a DC bus). The series converter can
inject a maximum of 10% of nominal line-to-ground voltage
in series with line L2.
In this simulation model the Power data parameters that
the series converter is rated 100 MVA
with a maximum voltage injection of 0.1 pu. The shunt
converter is also rated 100 MVA. Also in the control
parameters, that the shunt converter is in Voltage regulation
mode and that the series converter is in Power flow control
mode.
Results for 5-Bus system
Table 1 Results for 5-bus system without UPFC
Voltage
(pu)
0.997
0.9996
0.9996
0.9911
0.9974
Active
(MW)
68.27
563
560.4
925.7
1280
Power
Reactive
(MVAr)
-12.25
-59.16
-21.45
24.92
-110.5
Power
Table 2 Results for 5-bus system with UPFC
Voltage
(pu)
0.9982
1.004
1
0.9923
0.9981
Active
(MW)
152.1
645.4
643
840.8
12780
Power
Reactive
(MVAr)
-26.33
-95.18
-27
15.75
-100.8
Power
Table -1 shows that when UPFC is not connected in the
network, the actual active power flow is 68.27MW and
reactive power is -12.25 MVAr and voltage is 0.997 p.u.
After installation of UPFC at BUS B3, power flow from the
trf.2 will increase from 68.27MW to 152 MW with
decreasing of reactive power from -12.25MVAr to -26.33
MVAr with improving of voltage from 0.997 p.u.to 0.9982
p.u as shown in Table 2. In order the power flow will be
shared in the line -1, line-2 and line-3 with decrease in
overloading of Trf.2 (as results no.4 of table-1 &2), and
with improvement of voltage and decreasing of reactive
power.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Manish Raval and Ved Vyas Dwivedi
In test case we can see that the UPFC improves the
voltage level of the system buses and also the voltage angle
of the receiving end bus. So we can say that with help of
UPFC connected to the power system the overall
performance of the system improves.
After connection of UPFC in the substation, the power
flow will be regulated and overloading of the existing line
will be shared with other unloaded line means load
distributed on the other connected network, therefore
without erecting new transmission line we can use existing
infrastructure with installation of UPFC.
Conclusion
The test results show that the use of FACTS system in
the variable power flow transmission system maintain and
improve the power system operation, stability, and optimum
control of power flow increases the efficiency of
transmission network. The use of flexible transmission
system in the variable sources grid network balance the
system demand as well as optimize the existing transmission
system by unified power flow controller which provides
simultaneous or individual control of basic system
parameters like transmission voltage, impedance and phase
angle there by controlling the transmitted power. If the
UPFC is not connected in the network, the over loading on
line resulted in erection of new electrical line and substation
to full fill the system requirement But with the incorporation
of UPFC the power flow will be regulated and the existing
line will be used to fulfill the requirement of network and
remove the problem of evacuation of power.
The unscheduled interchange mechanism also needs to
be reviewed and frequency control through this mechanism
can perhaps be phased out and replaced by ancillary
services. The load dispatch centers need to be empowered so
they can take autonomous decisions relating to operation and
security of the grid. The role of technology in system
maintenance and up gradation is also important.
Transmission planning criteria need to be reviewed in light
of the growing complexity of the system. Then latter has
made the system vulnerable to cyber attacks, necessitating
appropriate solutions to be put in place.
The cost of UPFC is very much higher than other static
reactive power regulators and it is mostly suitable for more
than 220KV electrical system.
Acknowledgement: The authors express their gratitude to
Gujarat energy Transmission Company and Chief Electrical
Inspectorate Department of Gujarat to give technical support
for the collection of data and measurements.
References
[1]
Mandavising,Grid Gap,Evacuation concept for Wind
ProjectReneable
watch,May
2011
and
R.Billinton,L.Salvaderi,J.D.McCalley,H.Chao,The
eitz,R.N.Allan,J.Odom,C.Fallon,”Reliability
Issues
In
Today’s Electric Power Utility Environment”,IEEE
Transaction on Power Systems,Vol.12,No.4,November 1997.
103
[2]
L. Gyugyi, “Unified power flow concept for flexible ac
transmission systems,” IEE Proceedings-C, Vol. 139, Issue 4.
pp 323-331,1992.
[3] Ch. Chengaiah, G. V. Marutheswar and R. V. S. Satyanarayana,
“Control Setting Of Unified Power Flow Controller Through
Load Flow Calculation,” ARPN Journal of Engineering and
Applied Sciences, Vol.3, No.6, Dec 2008.
[4] S. Muthukrishnan and A. Nirmalkumar “Enhancement of Power
Quality in 14 Bus System using UPFC,” Research Journal of
Applied Sciences, Engg and Tech, 356-361, 2010.
[5] S.Muthukrishnan and Dr. A. Nirmal Kumar, “Comparison of
Simulation and ExperimentalResults of UPFC used for Power
Quality Improvement,” International J of Computer and
Electrical Engg, Vol. 2, No. 3, pp.1793-8163, June, 2010.
[6] V. Gupta, “Study and Effects of UPFC and its Control System
for Power Flow Control and Voltage Injection in a Power
System”, International Journal of Engineering Science and
Technology, Vol. 2(7), 2010, pp. 2558-2566.
[7] S. Panda, R, N. Patel, “Improving Power System Transient
StabilityWith An Off–Centre Location Of Shunt Facts
Devices”, Journal of ELECTRICAL ENGINEERING, Vol.
57, No. 6, 2006, pp. 365-368.
[8] N. G. Hingorani, “Flexible AC transmission”, IEEE Spectrum,
pp. 40-45, April 1993.
[9] M. H. Haque, “Application of UPFC to Enhance Transient
Stability Limit”, IEEE.
[10]M.Noroozain,L.Angquist,M.Ghandhari,G.Andersson,”Use of
UPFC for Optimal Power Control”IEEE Transactions on
Power Delovery,Vol.12,No.4,Oct.1997.
[11]Claudio A.Canizares,Edvina Uzunovic,John Reeve,’Transient
Stability and Power Flow model of UPFC for Various
Control Strategies’,International J Energy Tech Policy, 2005.
[12] S.Tara Kalyani,G.Tulasiram Das,”Simulation of Real and
Reactive Power Flow Control with UPFC connected to A
Tx’ne”, J of Theorotical Applied Information Tech,2008.
[13] Manish Raval, Ved Vyas Dwivedi, ‘Analytical Investigations
on Balancing the Electrical Grid Systems with the Injection
of Variable Wind Generation in Gujarat State – India’
Inventi Impact: Energy and Power vol. 2012, Issue-3 on
15/7/2012, www.inventi.in
Manishkumar N. Raval is a B.E. and M.E.
Electrical Engineering, and pursuing his Ph.D.
(in Electrical engineering) from Department of
Engineering, Pacific University, Udaipur,
Rajasthan, India under the guidance of
Professor
(Dr) Ved Vyas Dwivedi is Director, Noble
Group of Institutions, Junagadh, Gujarat,
(India). He is currently working as Assistant
lectrical Inspector, under the Electrical
Inspectorate, Government of Gujarat. He has participated in
many conferences and seminars. He has worked for the
statutory requirements of Electricity laws and Rules
prevailing in the State under the Departmental activities. His
field of interest and research are in Renewable energy
sources, Load flow studies, Power Quality and Load Side
Management.
Professor (Dr) Ved Vyas Dwivedi is a B.E., M.E., and
Ph.D., worked with Tata Chemicals Ltd., Elecon Engg. Co.
Ltd. and Valcan Engg. Co. Ltd. in various capacities starting
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Manish Raval and Ved Vyas Dwivedi
104
from G.E.T., Jr Engr, and Sr R & D Engr., in CIT Changa
and Charusat as Assist. and Assoc. Prof. and is currently
working as Professor (Gujarat Technological Univ.) and
Director (Noble Group of Institutions - Junagadh. He is life
member of IETE, IE, ISTE and member IEEE & MTT-S
(2003, '04, '09, '10). He has been offering his services as
reviewer of various national and international Journals such
as Doves - Journal of Nano technology and Sciences,
Journal of Computer Engineering, Journal of Electronics
researches, and reviewer of various international and
national conferences sponsored by IEEE, IETE and IE. He is
guiding seven Ph D candidates and has guided 32 M. Tech.
dissertations. He has published 54 Journal papers and 42
Conference papers. He has co-authored 06 books in
engineering & technology and co-chair of Junagadh-GTU
Innovation Sankul. He has filed 03 patents and is recipient of
four awards for excellene in education and service to the
professional education system. His Fields of interest and
research
are
wireless-optical-mobile-satellite
communication, radar -microwave-electromagnetic-antennaRF and Metamaterials, conventional/non conventional
energy generation-conservation-application engineering.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P.Pugazhendiran, M.Sujith and Dr.S.S.Jayachandran
105
Matlab Based HVCT Fault Analysis
P.Pugazhendiran, M.Sujith and Dr.S.S.Jayachandran
Abstract- The ageing and deterioration of insulation in high
voltage (HV) plants have been a source of concerns to utilities.
Breakdown of insulation leads to failures of HV equipment.
The ageing and eventual failure of insulation in a high voltage
current transformer (HVCT) is the subject of investigation in
this paper. A lumped parameter model of HVCT is developed.
This model is used to study the influence of deteriorating and
failed insulation on the state variables of the HVCT. Some
possible scenarios that could lead to a CT failure are
investigated in this paper. For all the scenarios considered,
steady and transient equations relating the state variables of
the model have been developed and analyzed. The objectives of
these analyses are to establish the behavioral characteristics of
the state variables, establish the interactions between these
variables, and investigate the possible generations of harmonics
under the various scenarios of deteriorating and outright
failure of insulation in the CT. The paper concludes with a
discussion of the results obtained.
Keywords: Current Transformer , High Voltage , Insulation.
I.INTRODUCTION
High voltage bushings and current transformers are among
the most vulnerable power systems equipment because they
are subjected to high dielectric and thermal stresses sudden
failure of a current transformer in the transmission
substation can cost a utility in excess of hundred thousands
of dollars in damage and loss of revenue. This cost alone is
for putting the system back to normal. It excludes cost
suffered by customer due to power loss and production lost
in some instances.
The failure pattern of current transformers in HV substations
has generally been violent, catastrophic and in some
instances near fatal. The nature of these failures makes it
difficult in most cases for a post-mortem technical
investigation to determine the root cause of the failure.
Therefore, in general, the phenomenon and processes
leading to this rather violent and sudden failure of HVCTs
are still not clearly understood.
P.Pugazhendiran and M.Sujith are with Department of Electrical and
Electronics Engineering, IFET College of Engineering, Villupuram-605108,
Tamilnadu, India and Dr.S.S.Jayachandran working as Principal, IFET
College of Engineering,Villupuram-605108, Tamilnadu, India, Emails:
pugazhifet@gmail.com, sujiifet@yahoo.in, ssjifet@gmail.com
Table 1: Failure Modes of CTs
Failure mode
Cause
Number
Insulation failure
Single phase faulted
Unknown
Pre-energization
Star point fault
Tank rupture
unspecified
unspecified
unspecified
unspecified
unspecified
unspecified
24
58
6
2
1
1
And investigation of the modes of failure revealed, as shown
in table 1, that the most common mode is when one of CT's
Phases has failed. Even then the root or primary cause of
failure could be anything, but it is suspected in most cases to
be insulation failure because the CTs were usually so badly
damaged this could not be ascertained.
It is believed that the processes leading to a total failure of
this equipment is complex. Failure could have started with a
gradual but progressive deterioration of insulation at any
part of the device. The failure of insulation at a sport in the
device could then initiate the cascading of other insulation
failures culminating in concurrent failures of insulation at
several parts of the device, resulting thus in the complete
failure of the equipment.
In an effort to seek solution to this problem of HVCT
failures this paper focuses on investigating the root ageing
and eventual failure of insulation at a location in a high
voltage current transformer (HVCT). A lumped parameter
model of HVCT is developed. This model is used to study
the influence of deteriorating and failed insulation at a
particular location on the state variables of the HVCT.
Root deterioration and failure of insulation is possible at
several parts of the equipment. This paper first investigates
insulation deterioration and failure within the primary
winding. It then considers deterioration and failure of
insulation between any sport on the primary winding and the
ground. For all the scenarios considered, steady and transient
equations relating the state variables of the model have been
developed and analyzed. The objectives of these analyses are
to establish the behavioral characteristics of the state
variables, establish the interaction between these variables,
and investigate the possible generations of harmonics under
the various scenarios of deteriorating and outright failure of
insulation in the CT. The paper concludes with a discussion
of the results obtained.
II. THE MODEL DEVELOPMENT
Figure shows is the developed model for the CT in figure
with all quantities and parameters referred to the primary.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P.Pugazhendiran, M.Sujith and Dr.S.S.Jayachandran
106
The insulator is modeled as a parallel combination of
resistance and capacitance because it is regarded as its
practical representation
(2)
Where Rp is the primary winding resistance and Xp is the
primary winding leakage reactance. The insulation
impedance may be expressed by:
(3)
Where Rins is the insulation resistance and Cins is the
insulation capacitance.
Fig.1. Eventual Failure of Primary Winding
The current through the secondary winding and the burden
may be expressed as:
(4)
The magnetizing current may thus be written as:
Fig.2. Breakdown Failure of Primary Winding and ground
A perfect insulation will be an open circuit, while a short
circuit is an indication of failure. The insulation deterioration
and its eventual failure within the primary winding is shown
in Figure 1. while the deterioration and eventual failure of
insulation between the primary winding and ground is
reflected in Figure 2.Breakdown voltage is a function of the
current flowing through the insulation. Therefore, it is
depicted by a current controlled voltage source.
The current to be transformed is depicted as the
current source Isource in the primary side of the circuit
model. This is the current flowing through the primary
winding. A fraction (n < 1) of the primary winding Zp is
separated from the rest by the location of the insulation
failure on the primary winding.
The magnetizing windings which link primary and
secondary windings are represented by parallel Combination
of magnetizing resistance (Rm) and inductance (Lm). The
secondary winding of the CT is represented by a resistance
(Rs) and a leakage inductance (Ls). The CT burden in the
secondary is represented by the resistance (R b) in series with
an inductance (Lb).
III STEADY STATE EQUATIONS
(5)
Where Zm is the magnetizing impedance, expressed as:
(6)
And Zsb is the series combination of secondary winding and
the burden impedances.
(7)
(B) Primary winding insulation failure to ground –
Breakdown Voltage ignored
The steady state equations governing the model in figure 2
with the breakdown voltage ignored are:
(8)
Where Zeq is the equivalent impedance of secondary, burden,
magnetizing and primary windings given as
(A) Insulation Failure within the Primary Winding
(9)
The steady state equations governing the model of Fig 1are:
(10)
(1)
Where Iins is the current leaking through an imperfect or
deteriorating insulation, Isource is the source current and Zp is
the primary winding impedance.
(11)
Inp is the current flow as indicated in figure 2(b),
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
P.Pugazhendiran, M.Sujith and Dr.S.S.Jayachandran
107
(12)
(C) Primary winding insulation failure to ground with
Breakdown Voltage
Using superposition principle the relevant steady
state equations for Figure 2 can be obtained as below.
Subscript 1 is for contribution when the current source is
open-circuited, while subscript 2 denotes quantities
contributed when the voltage source is short-circuited.
Fig 3 (a)
(13)
If the high voltage rating of the primary winding is Vprimary.
Then the breakdown voltage is
(14)
Iins-max is the maximum insulation current is possible which
will be Isource.
(15)
Where Inp1 and Inp2 are the current through nZp.
Fig 3 (b)
(16)
Fig 3:Results of the analysis of insulation breakdown within
primary winding only
IV ANALYSIS AND RESULTS
(A) Insulation Breakdown within Primary Windings only
With the aid of Matlab the steady-state equations in the
previous section were solved to obtain the variation of some
key quantities with changing state of inter-primary winding
insulation as shown in Figures 3(a),3(b)The variation of
insulation current with the insulation resistance and
capacitance are as in Figures 3(a) and 3(b)
respectively. For each figure, one of the insulation
parameters was kept constant at an assumed value, while the
other was varied. The family of curve displayed is as a result
of varying n, which depicts the position of
deteriorating/failing insulation along the primary winding.
Insulation resistance values of 1020 to 104 ohms represent
perfect insulation, but for 103 ohm and below the insulation
deteriorate and failed outright at the least value. Similarly,
capacitances of 10-14 to 100 Farads present perfect insulation,
while 101 to 103F deteriorating and then failed insulation. In
both cases the range for deterioration of insulation, during
which intervention could be made before outright failure, is
quite limited.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Fig 4 (a) Iins Vs Rins
Vol. 2, Issue. 1, April-2013.
P.Pugazhendiran, M.Sujith and Dr.S.S.Jayachandran
Fig 4 (b) Iins Vs Cins
(B) Insulation failure between primary winding and ground
Analysis as in the last section was repeated for the case of
insulation deterioration and failure to ground at different
locations on the primary winding, but with the breakdown
voltage ignored. The ensuring results, which are similar to
those above, are as shown in figure
With the breakdown voltage incorporated in the analysis the
steady-state results in figure 4(a) and 4(b) .These reflect the
same state change from good insulation to deteriorating and
failed insulation as observed so far. Zero to very low voltage
breakdown leads to insignificant contribution to current
flowing through that insulation. However, large value
breakdown results in large negative value of current
contribution to the insulation current. In proportion this
contribution of the breakdown voltage is quite significant
that it causes proportionality large current to flow in the rest
part of the device, thus resulting, on one hand, in the outright
burnt out of the device. On the other hand, the large currents
in the presence of magnetic fields produce large forces
responsible for the violent nature of the failure of the device.
V. CONCLUSION
A lumped parameter model suitable for investigating
insulation failure in a high voltage current transformer has
been proposed in this paper. This model has enabled the
study of the influence of deteriorating insulation before
complete failure in the primary windings of the transformer.
Two cases were investigated: insulation failure within
primary winding only, and between primary winding and
ground.
Three main outcomes are worthy of note:
* The current quantities are defined as the state variables of
the device; these variables are significantly influenced by the
change in the state of insulator at most points in the device.
These influences may be observable and could then be
monitored for quick intervention before a complete failure of
the equipment.
* The band on the insulation parameters scale between the
commencement of deterioration and complete failure of
insulation is quite narrow.
* The influence of failing insulation on the signal waveforms
within the device is insignificant. Consequently, there is no
significant generation of harmonics as a result of
deteriorating or failure of insulation in the device.
IV. REFERENCES
[1]. Van Bolliuis, Gulski E, Smith JJ, "Monitoring and
Diagnostic of Transformer Solid Insulation", IEEE
108
Transactions on Power Delivery, Vol. 17, No 2, March
2002.
[2]. Francisco das Chagas Fernandes Guerra , Wellington
Santos Mota, “A New current transformer model”, Revista
Controle & Automação/Vol.16 no.3/Julio, Agostoe
September 2005.
[3]. Hang Wang, Karen L. Butler, “Modeling Transformers
With Internal Incipient Faults”, IEEE Transactions on power
delivery, vol. 17, no. 2, April 2002
[4]. Mehmet Tu¨may, R. R. S. Simpson and H. El-Khatroushi2
“Dynamic model of a current transformer”, International
Journal of Electrical Engineering Education 37/3.
[5]. Demetrios A. Tziouvaras, Peter McLaren, George
Alexander, “Mathematical Models for Current, Voltage, and
Coupling Capacitor Voltage Transformers”, IEEE
transactions on power delivery, vol. 15, no. 1, January 2000.
[6]. http://-Av.mathworks.com
P.Pugazhendiran was born in Tamilnadu, in 1979.
Received his UG degree in Electrical and Electronics
Engineering from Coimbatore Institute of Technology
(CIT) in 2001 and PG degree from College of Engineering
Guindy (CEG), Anna University, Chennai in 2009. His
research interests includes Power quality issues, Power
Converters, Renewable energy sources, Electrical Drives.
He Published More than 5 Engineering Books. He published 7international
journals and Presented papers in 10 national and international conferences
Teaching Experience over a decade. He is currently working at I.F.E.T
College of Engineering as Associate Professor and head of the department.
He is a life member of ISTE.
M.Sujith was born in Namakkal, Tamilnadu in 1987.He
received the B.E. degree in Electrical and Electronics
Engineering from K.S.R.College of Engineering and
received M.E. degree in Applied Electronics from the
Annai Mathammal Sheela Engineering College. He
published 4 international journals and Presented papers in
6 national and international conferences. He is currently working at I.F.E.T
College of Engineering as Senior Assistant Professor. His main research
interests include power electronic converters, compensators and digital
communications
Dr.S.S.Jayachandran was born in Tamilnadu. He is
currently working as Principal in IFET College of
Engineering. He has served for 35 plus years at College
of Engineering, Guindy - Chennai, Central Polytechnic Chennai and TPEVR Govt. Polytechnic - Vellore. He has
been very much effective in Placement related activities.
He has to his credit over 66 publications and guided over 800 students. He
is a recognized Supervisor for guiding Ph.D and M.S (by research) under
Anna University, Chennai in the area of Safety, Quality Management and
Industrial Engineering. He has lead Accreditation process for 7 Engineering
programmes in 3 Institutions. He has also lead permanent Affiliation
process. He has been awarded certificate of merit by DTE. He has carried
out developmental works for over 100 industries and has conducted a
number of Staff & Student development training programs. He has carried
out several consultancy projects in the areas of Man Power Development
under CPS for Ministry of HRD, Vocational training scheme for TAHDCO
and Infrastructural Development Scheme for DRDA.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mashhood Hasan, Dinesh Kumar and Zafar Khan
109
Multimodules of Diode Clamped Multilevel
Converter: A Novel Option for High Power Facts
Controller
Mashhood Hasan, Dinesh Kumar and Zafar Khan
Abstract— This paper proposes a multimodules multilevel
diode clamped converter for a novel option high power FACTS
(Flexible AC Transmission System) controller. The various
configurations are being compared for high power FACTS
controlling devices and a mathematical design has been
developed for switching strategy considering fundamental
frequency. A switching pattern is developed for seven level two
module converter. There are six degree of freedom in the design
of the switching strategy which can mitigate lower order
harmonics and equally distribute current between two module.
Keywords— FACTs, Diode clamped,
Distortion, Multimodules, Multilevel.
Total
Harmonic
in series without increasing the individual thyristor rating,
provided the technology to ensure that the dc link voltages
are equal at all the levels is perfected. However, the clamping
diodes have to sustain the high voltage stress as the number
of levels increases. The voltage withstand of the diodes can
be increased by connecting several units in series. Unlike the
thyristors, the turning ON and OFF of the diodes do not
depend on gate-triggering so that passive circuits are
sufficient to ensure equalization of the voltage stresses in
steady-state and in transient.
I. INTRODUCTION
Proliferation in power electronics in the last few
decades have led to improvements in power devices and
novel concepts in converter topologies and control strategy
can improve the power quality. There are three types of
voltage source multilevel converters are recognized as
potential candidates for FACTS Controllers: (1) the
diode-clamped converter, (2) the flying-capacitors converter,
and (3) the cascaded-inverters with separated dc sources.
Now a days researchers is devoted to the diode-clamped
topology based multimodular FACTS controller devices for
high power application in a transmission line. However, brief
descriptions are given in below to all the 3 candidates and the
evaluations which have been made show that the
multimodular multilevel diode-clamped topology is the most
promising one.
Diode clamped multilevel converter which is shown in
Fig.1the structure of the diode-clamped multilevel converter
[2-6], which is actually an expanded version of Nabae's
Neutral-Point, 3-1evel converter [1]. In the structure, (N-l) dc
capacitors divide the total dc link voltage into N levels and
each half-Leg consists of (N-1) series-connected valves, with
each valve being interconnected to the corresponding level of
the dc capacitor via c1amping diodes. The idea is to limit the
voltage stress of the valves to the dc link capacitor voltage of
the jth level (j=1,2 ... N-1) with the help of these clamping
diodes. Thus the voltage ratings of the converter can be
increased by adding the number of levels that are connected
Mashhood
Hasan,
mirmashhood2010@gmail.com ,
Dinesh
Kumar
dinesh03211@gmail.com,
and
Zafar
Khan,
zafarkhan1069@rediffmail.com
Emails:
Fig.1
Flying-capacitor multilevel converter which is shown in
Fig.2 the structure of the flying-capacitor multilevel
converter [2]. In the structure, every pairing of the valves that
are symmetrically located on the phase legs is spanned by a
dc capacitor.
Fig.2
The size of the voltage increment between any
capacitor and the capacitor bracketing it on the outside
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mashhood Hasan, Dinesh Kumar and Zafar Khan
determines the size of the forward voltage stress of the
switching valves clamped by the two dc capacitors. For a
N-Level converter, it requires 6(N-l) switching valves and
(3N-5) dc capacitors. The structure appears to be simple and
symmetric. However, compared with diode-clamped
converter, it requires a large number of capacitors, which
normally entails the same number of complicated controllers
or independent dc power suppliers to maintain their voltages
at the specified levels.
110
The magnitude of fundamental harmonic of the ac output
voltage for Kth harmonics and mth module.
Vkm 
4Vdc
cos(k1m )  cos(k 2m )  cos(k3m )
3k
for k=1,3,5……
(1)
m=1,2
For eliminating lower order of harmonics and balancing the
currents in individual module if it is to be setting
Vk1  Vk 2  0
(2)
since cos( k im )  1 (i=1,2,3), it follows from (1) that
the Kth harmonic voltage of the mth module satisfies the
inequality.
Vkm 
4Vdc
k
(3)
th
as the filter reactance with respect to the K harmonic is
Fig.3
Cascade multilevel converter is shown in Fig.3 the structure
of the cascade multilevel inverters [7,8], in which full single
phase H-bridge inverter modules are connected in series,
with each module being fed by the voltage from a separate dc
capacitance. The N-Level cascaded-inverter uses 6(N-I)
switching va1ves and 3(N-l)/2 dc capacitors.
X k  jk L1
(4)
the magnitude of the kth current is
I km 
.as the
Vkm
4V
 2 dc
X k k  L1
(5)
I km in (5) varies inversely with K2, the square of the
harmonic number, the harmonic current decreases rapidly
with the increasing k. Furthermore, as even and triplen
harmonies do not exist, the lowest harmonies number not
already considered in the equalization of the rms voltage is
k=17 From (5), it is clear that the tilter inductance Li can be
quite economically sized without causing noticeable
unbalance.
III. COMPARISION AMONG THE
CONFIGURATION
Fig.
II. MATHEMATICAL DESIGN OF SWITCHING
STRATEGY
The mathematical calculation of Fundamental Frequency
Switching strategy [30-32] is preferred because it gives the
idea of Kth harmonics for mth module. Fundamental
Frequency Switching strategy is suitable for high power
converter. It requires only one switching at each cycle of the
utility standard frequency.
There are different configuration are evaluated for the
purpose of determining which is the most promising
structure to follow in the research of the thesis. In the
comparison, formulas of the components count of the
thyristors, the diodes, the capacitors etc. required for the four
different structures to implement the N-Level converter and
M module. Table 1.1 lists the number of solid switches, dc
capacitors and clamping diodes required to implement a
N-level converter and M module. Obviously, the cascade
structure and the flying-capacitance structure require more
capacitors and the diode-clamped structure needs more
clamping diodes.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mashhood Hasan, Dinesh Kumar and Zafar Khan
111
Diode clamped converter
Flying capacitor
converter
Cascaded
converter
Multimodules multilevel
diode clamped converter
Switching valve
6(N-1)
6(N-1)
6(N-1)
M*6(N-1)
Dc capacitor
(N-1)
(N-1)*(N-2)*3/2+(N-1)
3(N-1)/2
M*(N-1)
Clamping diode
(N-1)*(N-2)*3
0
0
M*(N-1)*(N-2)*3
Application in
FACTS
STATCOM,SSSC and
UPFC
STATCOM
STATCOM
STATCOM,SSSC and UPFC
Table 1.1 shows the comparative formulas for counting components
Compared with the diode-clamped structure both the cascade
structure and the flying-capacitor structure require many
more dc capacitors and complex capacitor voltage
controllers. In addition, both of them cannot be used for
application in the back-to-back rectifier converter dc link,
which is the core of the Unified Power Flow Controller
(UPFC) and the Asynchronous Link. Although the
diode-clamped structure will be required more c1amping
diodes, however it incurs less cost. .Unlike the other two
structures, the 3-phase legs of the diode-clamped structure
share the common series-connected dc capacitors. Therefore,
it can be used in almost all kinds of FACTS controllers,
including those based on the aforesaid back-to-back,
rectifier/inverter dc link Based on above comparisons, the
multimodules diode-clamped multilevel converter are
preferred.
IV.SIMULATION RESULT
The six unknown switching angles  im (i=1,2,3; m=1,2) in
Fig. c
V.CONCLUSION
Multimodules of diode clamped multilevel converter has
been seen multi advantage over various configuration. It
perform three major task (i) it achieve low total harmonic
distortion in voltage and current,(ii) direct fast control output
voltage magnitude (iii) equal distribution of current in
separate modules. This configuration adopted for all the
FACTS controlling device simply because of less cost and
easy controlling.
equations 1 and 2 are solved numerically using Matlab
software.
REFERENCES
[1] A Nabae, I.Takahashi, H.Akagi, "A new Neutral-Point-clamped
[2]
[3]
Fig. a
[4]
[5]
Fig. b
[6]
[7]
PWM Inverter," IEEE Transactions on Industry Applications,
Vol.IA-17, No.5, September/October 1981 pp.518-523.
C.Hochgraf, R.Lasseter, D.Divan, T.A.Lipo, "Comparison of
Multilevel Inverters for Static Var Compensation," IEEE IAS
'94 Annual Meeting Record, pp.92l-928.
R.W.Menzies, P.Steimer, J.K.Steinke, "Five-Level GTO
Inverters for Large Induction Motor Drives," IEEE transactions
on Industry Applications, Vo1.30 No.4, July/August 1994,
pp.938-944.
R.W.Menzies and Yiping Zhuang, "Advanced Statîc
Compensation Using a Multilevel GTO Thyristor Inverter,"
IEEE Transactions on Power Delivery, Vol. la, No.2, April
1995 pp.732-738.
J.B.Ekanayake, N.Jenkins, C.B.Cooper, “Experimental
Investigation of an Advanced Static VAr Compencsator" IEE
Proc.-Gener. Trans. Distrib., Vol.142, No.2, March 1995, pp.
202-210.
J.B.Ekanayake, N.Jenkins, "A Three-Level Advanced Staric
VAR Compensator," IEEE Transactions on Power Delivery,
Vol.11, No.l, January 1996, pp.540-545.
F.Z.Peng, J-8 Lai, J.Mckeever, J.VanCoevering, "A Multilevel
Voltage-source Inverter with Separate DC Sources for Statie
VAR Generation," IEEE lAS'95AnnualMeeting Record,
pp.2541-2548.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.
Mashhood Hasan, Dinesh Kumar and Zafar Khan
112
[8] F.Z.Peng, J-S Lai, "Dynamic Performance and Control of a
Static Var Generator Using Cascade Multilevel Inverters,”
IEEE IAS'96 Annual Meeting Record, pp.l009-1015
[9] B.Mwinyiwiwa, Z.Wolanski, Y.Chen, B.T.Ooi, "Multimodular
Multilevel Converters With Input/Output Linearity,” IEEE
Transactions
on
Industry
pplications,Vol.33,No.5,September/October 1997.
Mashhood Hasan received the B.E and M.Tech
degree from Jamia Millia Islamia(a central
university ) New Delhi ,India in 2003 and 2009. He
is a Ph.D. student from the same university. From
March 2004 to Sep 2006 he was a Lecturer in
electrical department at Al-Falah School of
Engineering and Technology India. Since Sep 2006 to august 2010
worked as Senior Lecturer in electrical department at IEC college
of Engineering and Technology, Gr Noida (UP). Presently, working
in GALGOTIAS college of Engineering and Technology in
Electrical Department, Gr Noida (UP), since august 2010 as a
Assistant Professor. His research interests in FACTS controlling
device, power system and power electronics.
Dinesh kumar received the B.E degree from
BCE Bhagalpur,Bihar (Government engineering
college) and Mtech from IET Ajmer,
Rajsthan,India in 2007 and 2012.From Sep 2007
to august 2010 he was a lecturer in in electrical
department of IEC college of engineering and
technology,Gr Noida (UP). Since Sep 2010 to January 2012 worked
as Senior Lecturer in electrical department at GNIT Girls Institute
of Technology, Gr Noida (UP). Presently, working in Dronacharya
college of engineering, Gr Noida (UP), since 28 th January 2013 as
a Assistant Professor.
Zafar khan received the B.E degree from
Jamia Millia Islamia (a central university )
New Delhi ,India in 2009. Right now he is
pursuing M.tech from Al Falah School of
engineering
and
technology,Dhouj
Faridabad, India. . From August 2009 to dec
2010 he worked with Voltas Ltd. As a
project engineer.. Presently, working in Al Falah School of
engineering and technology,Dhouj Faridabad, India. since 17
january as a Assistant Professor. His research interests in FACTS
controlling device, power system and power electronics.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE)
Vol. 2, Issue. 1, April-2013.