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International Journal of Advancements in Research & Technology, Volume 3, Issue 1, January-2014
ISSN 2278-7763.
Single Phase Unified Power Quality Conditioner
with Minimum VA requirement
B. Lakshmana Nayak1, V. Vijaya Kumar2
1
M.TECH(APS), AMIE, Assoc.Prof., NMR Engineering College, Hyderabad, A.P, India,
2
M.TECH, Assistant .Prof., NMR Engineering College, Hyderabad, A.P, India,
Abstract--This paper deals with “unified power
quality conditioners” (UPQCs) which aim to
integrate series active and shunt active filters. The
main purpose of a UPQC is to compensate for
voltage flicker/imbalance, reactive power, negative
sequence current and harmonics. It protects the
consumer at the load end from supply voltage sag,
and provides unity power factor condition at the
utility for different values of load power factor.
During the unbalanced voltage sag/swell at the
input side, the DVR maintains the rated voltage at
the load side. It regulates the load voltage with
minimum VA loading of the overall UPQC by an
optimum
voltage
angle
injection.
Some
experimental results of UPQC using MATLAB are
presented.
PLCs or adjustable-speed drives due to the
voltage sags is a serious power quality
concern for industrial customers. In [2],the
adjustable-speed drives have been reported
to trip for voltage sag as small as 15% for 8
ms. IEEE Std. 1346-1998 defines voltage
sag as a decrease in rms voltage at the
power frequency for duration of 0.5 cycle to
1 minute, caused by faults in the electric
supply system and staring of large loads like
induction motors.
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Index Terms— Active power filters, Dynamic
Voltage Restorer, optimized Unified Power Quality
Conditioner.
I.
INTRODUCTION
The wide application of the nonlinear and
switched
devices
in
electronically
distribution systems, the problems such as
voltage sag/swell, flicker, harmonics and
asymmetries of voltages have become
increasingly serious. Power electronics loads
inject harmonic currents in the ac system
and increase overall reactive power
demanded by the equivalent load. The other
development of the digital electronics
/communications and the process control
have increased the number of sensitive loads
that require ideal sinusoidal supply voltages
for the proper operation [1]. Spurious
tripping of voltage sensitive loads such as
Copyright © 2014 SciResPub.
Customers describe tripping of equipment
due to disturbances in the supply voltage as
“bad power quality”. The increased use of
converter-driven equipment, such as
consumer electronics, up to adjustable-speed
drives has led to a large growth of voltage
disturbances. The main cause here is the
non-sinusoidal current of rectifiers and
inverters. In view of the proliferation of the
power electronic equipment connected to the
utility system, various national and
international agencies have been considering
limits on harmonic current injection to
maintain good power quality. As a
consequence, various
standards
and
guidelines have been established that
specifies limits on the magnitudes of
harmonic currents and harmonic voltage
distortion at various harmonic frequencies.
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International Journal of Advancements in Research & Technology, Volume 3, Issue 1, January-2014
ISSN 2278-7763.
Some of these are as follows:
EN 50 006, "The Limitation of Disturbance in
Electricity Supply Networks caused by
Domestic and Similar Appliances Equipped
with Electronic Devices", European Standard
prepared by Comité Européen Electrotechnique,
CENELEC;
IEC Norm 555-3, prepared by the International
Electrical Commission;
West German Standards VDE 0838 for
household appliances, VDE 0160 for
converters, and VDE 0712 for fluorescent lamp
ballasts;
IEEE Guide for Harmonic Control and
Reactive Compensation of Static Power
Converters, ANSI/IEEE Std. 519-1981, which
was revised in 1992 to 519-1992.
CENELEC, IEC, and VDE standards
specify the limits on the voltage (as a
percentage of the nominal voltage) at
various harmonic frequencies of the utility
frequency, when the equipment-generated
harmonic currents are injected into a
network whose impedances are specified.
compensation principles were proposed
around 1980, much research has been done
on active filters in the last years [6], [7], [8].
Recent research effort have been made
towards utilizing a device called Unified
Power Quality
conditioner (UPQC) to
solve almost all power quality problems [9],
[10],[11]. To put in nutshell, UPQC aims the
integration of series active and shunt active
power filters connected through a common
dc-link capacitor. This led to the
development of advanced control techniques
for UPQC. In [12] some works have been
done based on the quadrature voltage
injection by the series-converter of the
UPQC. This scheme, leads to purely reactive
power handling by the series-converter, does
not result in a minimum VA consumption of
the overall UPQC, cannot operate for supply
voltage swell, and is not optimized from
point of view of VA loading and efficiency.
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The revised IEEE-519, which contains
recommended practices and requirements
for harmonic control in electric power
systems, specifies requirements on the user
as well as on the utility. Under this
circumstances, a new technology called
Custom Power emerged [3], which is
applicable to distribution systems for
enhancing the reliability and quality of
power supply. Custom power devices
include static shunt converter and static
series-converter. Static shunt-converters,
such as DSTATCOM, are mainly intended
for conditioning the current flowing from
the load into utility [4]. The series
converters, such as DVR, are used to
improve the quality of the voltage supplied
by the utility to the load [5]. Since the basic
Copyright © 2014 SciResPub.
The series voltage injection at an
optimized angle not only results in load
voltage regulation but also in overall
minimized VA loading and improved
efficiency. This paper presents an optimized
UPQC where the series voltage injection is
controlled at an optimized angle
for
minimum VA loading of the overall UPQC.
To verify and validate the proposed Power
Conditioning equipment and the control
method, a laboratory prototype was
performed; the system is fully digitalcontrolled
using
the
fixed-point
TMS320F240 digital signal processor.
The proposed Unified Power Quality
Conditioner has the following goals and
characteristics:
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International Journal of Advancements in Research & Technology, Volume 3, Issue 1, January-2014
ISSN 2278-7763.
The overall UPQC VA loading is
maintained at a minimum value for the
whole range of operation;
Maintains the load voltage at the rated
voltage for supply voltage sag/swell;
the injection voltage assured by seriesconverter is taken from the same dclink voltage controlled at a fixed level
(450VDC) by shunt-converter;
Compensates the load reactive power,
by controlling the current of shuntconverter; in steady-state operation, at
the rated supply-voltage, no active
power is consumed by shunt-converter;
Assures an input current with very low
harmonic content, having in view the
regulations of the previous mentioned
standards.
The series-connected converter such as
DVR, inject/extract the necessary voltage to
compensate the supply-voltage sag/swell.
The shunt-converter, such as STATCOM
(STATic
synchronous
COMpensator),
connected in parallel with the load takes a
current from the supply to compensate the
reactive power requested by the load, to
reduce the harmonics and to control the dclink voltage at a desired value. Shuntconverter acts not only as an active filter,
but assures the necessary active power for
series-converter, as well. The shuntconverter can operate with hysteresis current
control mode to force the source current Ii,
in the same phase with Ui such the input
power factor is always maintained unity.
The series-inverter operates in unipolar
PWM switching mode. When voltage
sag/swell occurs, the DVR injects a voltage
in such a manner so that the load end
voltage is always maintained at the desired
magnitude. There are two main methods for
load voltage compensation. As [12]
presents, when voltage sag occurs, the DVR
injects a voltage in quadrature advance to
the supply voltage. This method cannot be
used for compensation of the voltage swell,
and the overall UPQC VA loading is not
minimized. Another method, as [9] presents,
is the controlling of the compensating
voltage in the same phase or opposite phase,
depending on the supply voltage event. In
this case the UPQC is capable of
compensating both voltage sag and swell,
being not optimized from point of view of
UPQC VA loading.
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In this paper, the analysis, design and
experimental results are presented to show
the feasibility of the proposed scheme.
II. BASIC CONFIGURATION OF THE UNIFIED POWER
QUALITY CONDITIONER
The configuration of the UPQC is
presented in Fig.1. The UPQC consists of
two
single-phase
PWM
controlled
converters connected in cascade through a
common dc-link capacitor and a series lowimpedance transformer.
Fig 1. Single-phase Unified Power Quality Conditioner system.
Copyright © 2014 SciResPub.
The main advantage of the shunt-series
controller is that it does not require any
energy storage. It is designed to mitigate any
supply-voltage variation of a certain
magnitude, independent of its duration.
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International Journal of Advancements in Research & Technology, Volume 3, Issue 1, January-2014
ISSN 2278-7763.
A.
PHASOR DIAGRAM
Since the STATCOM is locally supplying
the reactive current component of the load
and VS1 is in phase with the PCC voltage
(VPCC) the source current IS1 is the real
component of the load current. Therefore,
and (1) can be rewritten as Therefore, IL cos
Ø = IS1 and (1) can be rewritten as
I s 2 = I L . cos(Φ) /(1 − x)
III.
VA REQUIREMENT
OPTIMUM UPQC
Fig. 2 Phasor representation of various currents and voltages in
UPQC
In case of a voltage sag, the postsag
source voltage (VS2) is given as VS2 =
VS1(1-x) ,where x is per-unit sag. Now, to
maintain active power constant under the
voltage sag condition, the following
equation can be written as
Vs1 I s1 = Vs 2 I s 2 ⇒ I s1 = (1 − X ).I s 2
Copyright © 2014 SciResPub.
THE
Because the shunt-converter has the
main role to assure an input current with a
very low THDi, this is connected and
controlled in a such way to compensate the
distortion component of the load current
(IdisL=IdisSh).The THDSh (Total Harmonic
Distortion of shunt-converter current, IC) is
one of the main factors, which affects the
VA ratings of the UPQC. It is very
important to find a relationship with THDL
(Total Harmonic Distortion of the load
current IL).
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The authors [8] reported a control scheme
considering minimum energy requirement
only for the DVR. There is no report on the
overall UPQC optimization where the
combined operation of DVR and
STATCOM has been taken into account.
The loading calculation of UPQC during the
voltage sag has been carried out on the basis
of a linear load for fundamental frequency at
rated load current ( ILRated). From the
phasor diagram of Fig. the presag source
voltage VS1 and load voltage ( VL2) during
the sag are assumed to be equal to the
healthy source voltage VS, which is 1 p.u.
Let the rated load current ( ILRated) a load
power factor angle be 1 p.u. with Ø1.
OF
Series
VA
Vinj .I s 2 = Vinj .I L . cos(Φ) /(1 − x)
loading
Shunt VA loading = IC2VL2+ IC22 ZSLC P.U
2
VA(total ) = Vinj .I L . cos(Φ ) /(1 − x) + I c 2 .V L 2 + I C 2 .Z slc P.u
-----------(1)
Equation (1) shows that at rated load current
( IL rated = 1 p.u), the total VA loading of
the UPQC is the function of three quantities,
viz. x, ø and θ,, and sag x and p.f. angle ø are
independent quantities. θ is the angle by
which leads the postsag voltage . The
voltage is injected by the DVR at an angle L
w.r.t postsag as shown in Fig.2. By applying
any standard method for function
minimization with x and ø
as two
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International Journal of Advancements in Research & Technology, Volume 3, Issue 1, January-2014
ISSN 2278-7763.
constraints and as a variable varying from 0
to 90 , an optimum angle θ can be found out,
that results in minimum total VA loading.
IV.
SIMULATION RESULTS
The results presented in this paper are for
a diode bridge rectifier with the non-linear
load at dc side - an inductance L in series
with a parallel RC load.
Fig.3.(b) - Rectifier bridge load - L=5mH, R=4Ω, C=20µF
THDL=0.18; THDSh=0.94; THDi=0.001.
Figure.3. Distortion compensation and power factor correction.
1 - Supply-voltage (320V/div); 2 - Load current;
3 - Input current; 4 - Compensating current; (80A/div; time 5ms/div)
In Fig.3.a and Fig.3.b there are shown
from top to bottom supply-voltage, load
current, input current and compensating
current-shunt-converter, for two different
loads.
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Figure. 4. Load Voltage compensation.
Ui sag from 220V to 154V; γ = 410;UTr = 79.5V. (200V/div,
20ms/div).1-Supply-voltage; 2-Peak supply-voltage; 3-Injected
voltage; 4-Load voltage
Fig 3.(a) - Rectifier bridge load - L=3mH, R=4Ω, C=1,500µF
THDL=0.37; THDSh=0.82; THDi=0.001.
V.
CONCLUSION
Voltage compensation method both for
supply voltage sag and swell also shows a
very good performance. The power factor is
improved at unity by compensation. The
load voltage is maintained at its reference
value. UPQC operates in the minimum VA
optimization mode; the optimized operation
can result not only in reduced overall size,
but also in the increased efficiency.
From the experimental results, one can say
that the proposed control methods have good
compensation characteristics and the
proposed UPQC system can have an
important
role
for
power
quality
improvement.
Copyright © 2014 SciResPub.
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International Journal of Advancements in Research & Technology, Volume 3, Issue 1, January-2014
ISSN 2278-7763.
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AUTHORS
First Mr. B. Lakshmana
Nayak, Born on 15th June
Anigandlapadu,
1980,
Andhra Pradesh, India. He
received
the
B.Tech.
Degree in Electrical and
Electronic
Engineering
from Sri Sarathi Institute of Engineering and
Technology, Nuzvid, Andhra Pradesh, and
M.Tech. Degree in Advanced Power System
from the Jawaharlal Nehru technological
university, Kakinada, Andhra Pradesh.
Presently he has been working as a
Associate Professor in the Electrical and
Electronic Engineering Department in Nalla
Malla
Reddy
Engineering
College,
Hyderabad, Andhra Pradesh, India. He has 8
years of experience. His main research area
power systems.
Email: lakshmananayak@gmail.com
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Copyright © 2014 SciResPub.
Second Mr. V. Vijaya
Kumar, Born on 8th May
1983, Shad Nagar, Andhra
Pradesh,
India.
He
received
the
B.Tech.
Degree in Electrical and
Electronic
Engineering
from Sri Saijothi Engineering college,
Mahabubnagar, Andhra Pradesh, and
M.Tech. Degree in Electrical Power System
from J. B. I. E. T, Andhra Pradesh.
Presently he has been working as a
Assistant Professor in the Electrical and
Electronic Engineering Department in Nalla
Malla
Reddy
Engineering
College,
Hyderabad, Andhra Pradesh, India. He has 7
years of experience. His main research area
power systems.
Email: vijay.victory.259@gmail.com
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