WWW.IJITECH.ORG
ISSN 2321-8665
Vol.03,Issue.04,
July-2015,
Pages:0559-0565
Control and Performance of DVR with Fuzzy Logic Controller
J. NAVEEN1, K. SRAVANTHI2
1
PG Scholar, Vijaya Engineering College, Khammam, T.S, India.
Assistant Prof, Vijaya Engineering College, Khammam, T.S, India.
2
Abstract: With this papers, distinct voltage injection plans
intended for Dynamic l voltage restorers (DVRs) usually are
analyzed using distinct give attention to the latest procedure
accustomed to decrease the score on the voltage supply
converter (VSC) utilised in DVR. A fresh control approach is
usually recommended to regulate the capacitor-supported
DVR. The particular control connected with some sort of
DVR is usually proven that has a reduced-rating VSC. The
particular guide fill voltage is usually projected when using
the device vectors. The particular synchronous guide body
concept can be used for that alteration connected with
voltages coming from turning vectors on the standing body.
The particular settlement connected with the voltage sag,
swell, as well as harmonics is usually proven utilizing a
reduced-rating DVR.
Keywords: Dynamic Voltage Restorers (DVRs), Voltage
Supply Converter (VSC).
I. INTRODUCTION
Power quality problems in the present-day distribution
systems are addressed in the literature due to the increased
use of sensitive and critical equipment pieces such as
communication network, process industries, and precise
manufacturing processes. Power quality problems such as
transients, sags, swells, and other distortions to the sinusoidal
waveform of the supply voltage affect the performance of
these equipment pieces. Technologies such as custom power
devices are emerged to provide protection against power
quality problems. Custom power devices are mainly of three
categories such as series-connected compensators known as
dynamic voltage restorers (DVRs), shunt-connected
compensators such as distribution static compensators, and a
combination of series and shunt-connected compensators
known as unified power quality conditioner. The DVR can
regulate the load voltage from the problems such as sag,
swell, and harmonics in the supply voltages. Hence, it can
protect the critical consumer loads from tripping and
consequent losses. The custom power devices are developed
and installed at consumer point to meet the power quality
standards such as IEEE-51. Voltage sags in an electrical grid
are not always possible to avoid because of the finite clearing
time of the faults that cause the voltage sags and the
propagation of sags from the transmission and distribution
systems to the low-voltage loads. Voltage sags are the
common reasons for interruption in production plants and for
end-user equipment malfunctions in general. In particular,
tripping of equipment in a production line can cause
production interruption and significant costs due to loss of
production.
One solution to this problem is to make the equipment
itself more tolerant to sags, either by intelligent control or by
storing ―ride-through‖ energy in the equipment. An
alternative solution, instead of modifying each component in
a plant to be tolerant against voltage sags, is to install a plant
wide uninterruptible power supply system for longer power
interruptions or a DVR on the incoming supply to mitigate
voltage sags for shorter periods. DVRs can eliminate most of
the sags and minimize the risk of load tripping for very deep
sags, but their main drawbacks are their standby losses, the
equipment cost, and also the protection scheme required for
downstream short circuits. Many solutions and their problems
using DVRs are reported, such as the voltages in a threephase system are balanced and an energy-optimized control
of DVR is discussed in. Industrial examples of DVRs are
given in, and different control methods are analyzed for
different types of voltage sags in. A comparison of different
topologies and control methods is presented for a DVR in.
The design of a capacitor-supported DVR that protects sag,
swell, distortion, or unbalance in the supply voltages is
discussed in. The performance of a DVR with the highfrequency-link transformer is discussed in. In this paper, the
control and performance of a DVR are demonstrated with a
reduced-rating voltage source converter (VSC). The
synchronous reference frame (SRF) theory is used for the
control of the DVR.
II. OPERATION OF DVR
A. Introduction
The major objectives are to increase the capacity
utilization of distribution feeders (by minimizing the rms
values of the line currents for a specified power demand),
reduce the losses and improve power quality at the load bus.
The major assumption was to neglect the variations In the
source voltages. This essentially implies that the dynamics of
the source voltage is much slower than the load dynamics.
Uncompensated nonlinear loads in the distribution system can
cause harmonic components in the supply voltages. To
mitigate the problems caused by poor quality of power
Copyright @ 2015 IJIT. All rights reserved.
J. NAVEEN, K. SRAVANTHI
supply, series connected compensators are used. These are
voltage sag, the particular voltage is reduced to Versus
called as Dynamic Voltage Restorer (DVR) in the literature
having a phase lag perspective connected with θ. Currently,
as their primary application is to compensate for voltage sags
the particular DVR injects the voltage such that the strain
and swells. Since then, several DVRs have been installed to
voltage degree is managed with the pre-sag issue. According
protect microprocessor fabrication plants, paper mills etc.
to the phase perspective in the heap voltage, the particular
Typically, DVRs are made of modular design with a module
shot connected with voltages may be recognized throughout a
rating of 2 MVA or 5 MVA. They have been installed in
number of methods. Vinj1 shows the particular voltage shot
substations of voltage rating from 11 kV to 69 kV. A DVR
in-phase with the source voltage. With all the shot connected
has to supply energy to the load during the voltage sags. If a
with Vinj2, the strain voltage degree is always identical but it
DVR has to supply active power over longer periods, it is
brings Versus by the little perspective. With Vinj3, the strain
convenient to provide a shunt converter that is connected to
voltage keeps the identical phase seeing that that in the prethe DVR on the DC side. In this section, we discuss the
sag issue, which can be the perfect perspective taking into
application of DVR for fundamental frequency voltage. The
consideration the power source. Vinj4 would be the issue
voltage source converter is typically one or more converters
where the shot voltage is within quadrature with the latest,
connected in series to provide the required voltage rating. The
and this also circumstance is suitable for just a capacitorDVR can inject a (fundamental frequency) voltage in each
supported DVR seeing that this specific shot requires not any
phase of required magnitude and phase. The DVR has two
productive electric power. Nevertheless, a minimum possible
operating modes
rating in the converter is accomplished simply by Vinj1. This
1. Standby (also termed as short circuit operation (SCO)
DVR is operated within this plan having a electric battery
mode) where the voltage injected has zero magnitude.
power safe-keeping process (BESS).
2. Boost (when the DVR injects a required voltage of
appropriate magnitude and phase to restore the pre-fault
load bus voltage).
The power circuit of DVR shown in Fig 1 has four
components listed below.
B. Voltage Source Converter (VSC)
This could be a 3 phase – 3 wire VSC or 3 phases – 4 wire
VSC. The latter permits the injection of zero-sequence
voltages. Either a conventional two level converter (Graetz
Bridge) or a three level converter is used.
Fig2. (a) Basic circuit of DVR. (b) Phasor diagram of the
DVR voltage.
Fig1. Dynamic Voltage Restorer.
This schematic of the DVR-connected process is proven
throughout Fig. a couple of. 2(a). This voltage Vinj is
introduced such that the strain voltage Vload is constant
throughout degree and it is undistorted, although the source
voltage Versus is not constant throughout degree or even is
altered. Fig.2. 1(b) demonstrates the particular phasor
diagram connected with different voltage shot strategies. shot
strategies in the DVR. VL(pre−sag) is often a voltage along
the important heap prior to voltage sag issue. Throughout the
Fig. 3 shows a schematic of a three-phase DVR connected
to restore the voltage of a three-phase critical load. A threephase supply is connected to a critical and sensitive load
through a three-phase series injection transformer. The
equivalent voltage of the supply of phase A vMa is connected
to the point of common coupling (PCC) vSa through shortcircuit impedance Zsa. The voltage injected by the DVR in
phase A vCa is such that the load voltage vLa is of rated
magnitude and undistorted. A three-phase DVR is connected
to the line to inject a voltage in series using three single-phase
transformers Tr. Lr and Cr represent the filter components
used to filter the ripples in the injected voltage. A three-leg
VSC with insulated-gate bipolar transistors (IGBTs) is used
as a DVR, and a BESS is connected to its dc bus.
International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0559-0565
Control And Performance Of DVR With Fuzzy Logic Controller
phase machine can be represented by an two-phase machine
as shown in 4(b), where ds-qs correspond to stator direct and
quadrature axes, and dr-qr correspond to rotor direct and
quadrature axes. Which, in effect, replaced the variables
(voltages, currents and flux linkages) associated with the
stator windings of synchronous machine with variables
associated with fictitious windings rotating with the rotor
with synchronous speed. Essentially, he transformed, or
referred, the stator variables to a synchronously rotating
reference frame fixed in the rotor. With such transformation
(called park’s transformation), he showed that all the timevarying inductances that occur due to an electric circuit in
relative motion and electric circuits with varying magnetic
reluctances can be eliminated. Later, in Without going deep
in to rigor of machine analysis, we will try to develop a
dynamic machine model in a synchronously rotating and
stationary reference frames.
Fig3. Schematic of the DVR-connected system.
III. CONTROL OF DVR
A. Introduction
The compensation for voltage sags using a DVR can be
performed by injecting or absorbing the reactive power or the
real power. When the injected voltage is in quadrature with
the current at the fundamental frequency, the compensation is
made by injecting reactive power and the DVR is with a Selfsupported dc bus. However, if the injected voltage is in phase
with the current, DVR injects real power, and hence, a battery
is required at the dc bus of the VSC. The control technique
adopted should consider the limitations such as the voltage
injection capability (converter and transformer rating) and
optimization of the size of energy storage
C. Control of DVR with BESS for Voltage Sag, Swell, and
Harmonics Compensation
Fig.5 shows a control block of the DVR in which the SRF
theory is used for reference signal estimation. The voltages at
the PCC vS and at the load terminal vL are sensed for
deriving the IGBTs’ gate signals. The reference load voltage
V*L is extracted using the derived unit vector. Load voltages
(VLa, VLb, VLc) are converted to the rotating reference
frame using abc−dqo conversion using Park’s transformation
with unit vectors (sin, θ, cos, θ) derived using a phase-locked
loop as
(1)
B. Dynamic d-q Model
The dynamic performance of an ac machine is somewhat
complex because the three-phase rotor windings move with
respect to the three-phase stator windings as shown in figure
4(a).
Similarly, reference load voltages
(2)
(3)
And voltages at the PCC vS are also converted to the
rotating reference frame. The reference DVR voltages are
obtained in the rotating reference frame as
(4)
(a)
(b)
Fig4. (a) Coupling effect in three-phase (b). Equivalent twophase machine stator and rotor windings.
(5)
The error between the reference and actual DVR voltages
in the rotating reference frame is regulated using two
proportional–integral (PI) controllers. Reference DVR
voltages in the abc frame are obtained from a reverse Park’s
transformation taking
V * Dd from (4), V *
Basically, it can be looked on a s a transformer with a
(6)
moving secondary, where the coupling coefficients between
Reference DVR voltages (v* dvra, v* dvrb, v* dvrc) and
the stator and rotor phases change continuously with the
actual DVR voltages (vdvra, vdvrb, vdvrc) are used in a pulse
change of rotor position θr. The machine can be described by
width modulated (PWM) controller to generate gating pulses
differential equations with time-varying mutual inductances,
to a VSC of the DVR. The PWM controller is operated with a
but such a model tends to be very complex. Note that a threeswitching frequency of 10 kHz.
International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0559-0565
J. NAVEEN, K. SRAVANTHI
should be of rated magnitude and undistorted. In order to
maintain the dc bus voltage of the self-supported capacitor, a
PI controller is used at the dc bus voltage of the
Vcap(n)=vcap(n−1)+Kp1_vde(n)–vde(n−1)+Ki1vde(n) (9)
Fig5. Control block of the DVR that uses the SRF method
of control.
Where vde (n) = v* dc – vdc (n) is the error between the
reference v* dc and sensed dc voltages vdc at the nth
sampling instant. Kp1 and Ki1 are the proportional and the
integral gains of the dc bus voltage PI controller. The
reference d-axis load voltage is therefore expressed as
follows:
v*d = vddc − vcap
(10)
The amplitude of load terminal voltage VL is controlled to
its reference voltage V *L using another PI controller. The
output of the PI controller is considered as the reactive
component of voltage vqr for voltage regulation of the load
terminal voltage. The amplitude of load voltage VL at the
PCC is calculated from the ac voltages (vLa, vLb, vLc) as
VL = (2/3)v2La + v2Lb + v2Lc
(11)
Then, a PI controller is used to regulate this to a reference
value as
vqr(n)=vqr(n−1)+Kpvte(n)−vte(n−1)+Ki2vte(n) (12)
Where, vte(n) = V*L− VL(n)
Denotes the error between the reference V* L and actual
VL (n) load terminal voltage amplitudes at the nth sampling
instant. Kp2 and Ki2 are the proportional and the integral
gains of the dc bus voltage PI controller. The reference load
quadrature axis voltage is expressed as follows:
V*q = vqdc + vqr
Fig6. (a) Schematic of the self-supported DVR. (b)
Control block of the DVR that uses the SRF method of
control.
(13)
Reference load voltages (v*La, v*Lb, v*Lc) in the abc frame
are obtained from a reverse Park’s transformation as in (6).
The error between sensed load voltages (vLa, vLb, vLc) and
reference load voltages is used over a controller to generate
gating pulses to the VSC of the DVR.
IV. FUZZY LOGIC CONTROLLER
A. Introduction
Fuzzy logic is an innovative technology that enhances
D. Control of Self-Supported DVR for Voltage Sag, Swell,
conventional
system design with engineering expertise. Using
and Harmonics Compensation
fuzzy
logic,
we can circumvent the need for rigorous
Fig.6 (a) shows a schematic of a capacitor-supported
mathematical
modeling A human operator is far more
DVR connected to three-phase critical loads, Fig.6 (b) shows
successful in controlling a process than a controller designed
a control block of the DVR in which the SRF theory is used
by modern analytical technique. So it is worth simulating the
for the control of self-supported DVR. Voltages at the PCC
control strategy based upon intuition and experience and can
vS are converted to the rotating reference frame using
be considered as heuristic decision or rule of thumb decision.
abc−dqo conversion using Park’s transformation. The
In academic and technological arena, Fuzzy is a technical
harmonics and the oscillatory components of the voltage are
term that deals with ambiguity or vagueness based on human
eliminated using lowpass filters (LPFs). The components of
intuitions. Professor Lotfi A Zadeh introduced the concept of
voltages in the d- and q-axes are
fuzzy sets, according to him. Fuzzy logic is a mathematical
vd =vddc + vdac
(7)
imprecise description. During the past several years, FLC has
emerged as one of the most active area of research for the
vq =vqdc + vqac
(8)
application of fuzzy set theory. A fuzzy set is a generalization
The compensating strategy for compensation of voltage
of the concept of an ordinary set in which the membership
quality problems considers that the load terminal voltage
function (MF) values can be only one of the two values, 0 and
International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0559-0565
Control And Performance Of DVR With Fuzzy Logic Controller
1. A fuzzy set can be defined as below. Fuzzy set A in a
universe of discourse U is characterized by a MF A: U  [0]
[1] and associates with each element x of U a number A (x)
in the interval [0 1] representing the degree of membership of
x in A.
B. Fuzzy Controller Model
Fuzzy modeling is the method of describing the
characteristics of a system using fuzzy inference rules. The
method has a distinguishing feature in that it can express
linguistically complex non-linear system. It is however, very
hand to identify the rules and tune the membership functions
of the reasoning. Fuzzy Controllers are normally built with
fuzzy rules. These fuzzy rules are obtained either from
domain experts or by observing the people who are currently
doing the control. The membership functions for the fuzzy
sets will be derive from the information available from the
domain experts and/or observed control actions.
Fig8. Simulation model diagram of the BESS-supported
DVR-connected system.
Fig9. Dynamic performance of DVR with in-phase
injection during voltage sag and swell applied to critical
load.
Fig7. Structure of Fuzzy Logic controller.
The building of such rules and membership functions
require tuning. That is, performance of the controller must be
measured and the membership functions and rules adjusted
based upon the performance. This process will be time
consuming. The basic configuration of Fuzzy logic control
based as shown in Fig.7 consists of four main parts i.e. (i)
Fuzzification, (ii) knowledge base, (iii) Inference Engine and
(iv) Defuzzification.
Fig10. Source voltage.
V. MODELING AND SIMULATION
The DVR-connected system consisting of a three-phase
supply, three-phase critical loads, and the series injection
transformers shown in Fig.8 is modeled in MATLAB/
Simulink environment along with a sim power system
toolbox and is shown in Fig 8 the control algorithm for the
DVR shown in Fig. 5 is also modeled in MATLAB. The
reference DVR voltages are derived from sensed PCC
voltages (vsa, vsb, vsc) and load voltages (vLa, vLb, vLc). A
PWM controller is used over the reference and sensed DVR
voltages to generate the gating signals for the IGBTs of the
VSC of the DVR. The capacitor-supported DVR shown in
Fig.6 is also modeled and simulated in MATLAB, and the
performances of the systems are compared in three conditions
Fig. 11.Load voltage Source and load rms voltages.
of the DVR.
International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0559-0565
J. NAVEEN, K. SRAVANTHI
Fig.12.Dvr injected voltages outputs fuzzy
Fig13. Dynamic performance of DVR with in-phase
injection during voltage sag and swell applied to critical
load.
Fig.14.Source voltage.
Fig.16.Dvr injected voltages.
VI. CONCLUSION
Here functioning of an DVR continues to be exhibited that
has a brand new handle technique employing various voltage
hypodermic injection strategies. A comparison on the
efficiency on the DVR having various strategies continues to
be carried out that has a reduced-rating VSC, which include a
capacitor-supported DVR. Your reference point weight
voltage continues to be predicted while using means of
product vectors, along with the handle of DVR continues to
be realized, which in turn minimizes your miscalculation of
voltage hypodermic injection. Your SRF hypothesis
continues to be useful for price your reference point DVR
voltages. It really is concluded that your voltage hypodermic
injection in-phase with the PCC voltage results in minimum
status of DVR although at the price of a power source at their
dc bus.
VII. REFERENCES
[1] M. H. J. Bollen, Understanding Power Quality
Problems—Voltage Sags and Interruptions. New York, NY,
USA: IEEE Press, 2000.
[2] A. Ghosh and G. Ledwich, Power Quality Enhancement
Using Custom Power Devices. London, U.K.: Kluwer, 2002.
[3] M. H. J. Bollen and I. Gu, Signal Processing of Power
Quality Disturbances. Hoboken, NJ, USA: Wiley-IEEE Press,
2006.
[4] R. C. Dugan, M. F. McGranaghan, and H. W. Beaty,
Electric Power Systems Quality, 2nd ed. New York, NY,
USA: McGraw-Hill, 2006.
[5] A. Moreno-Munoz, Power Quality: Mitigation
Technologies in a Distributed Environment. London, U.K.:
Springer-Verlag, 2007.
[6] K. R. Padiyar, FACTS Controllers in Transmission and
Distribution. New Delhi, India: New Age Int., 2007.
[7] IEEE Recommended Practices and Recommendations for
Harmonics Control in Electric Power Systems, IEEE Std.
519, 1992.
[8] V. B. Bhavraju and P. N. Enjeti, ―An active line
conditioner to balance voltages in a three phase system,‖
IEEE Trans. Ind. Appl., vol. 32, no. 2, pp. 287–292,
Mar./Apr. 1996.
[9] S. Middlekauff and E. Collins, ―System and customer
impact,‖ IEEE Trans. Power Del., vol. 13, no. 1, pp. 278–
282, Jan. 1998.
Fig.15.Load voltage Source and load rms voltages
International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0559-0565
Control And Performance Of DVR With Fuzzy Logic Controller
[10] M. Vilathgamuwa, R. Perera, S. Choi, and K. Tseng,
―Control of energy optimized dynamic voltage restorer,‖ in
Proc. IEEE IECON, 1999, vol. 2, pp. 873–878.
Author’s Profile:
J.Naveen, Received B.Tech Degree In
Electrical And Electronics Engineering
From Swarna Bharathi College Of
Engineering College, Maddulapally,
Khammam, A.P. And Currently Pursuing
M.Tech In Power Electronics At Vijaya
Engineering College,Khammam,T.S. My
Areas Of Interest Are Power Systems, And
Power Electronics, Electrical Machines.
K.Sravanthi, presently working as
Associate Professor & Head of the
Department in Vijaya Engineering
College, Khammam, T.S, India. She
received her B.Tech degree in Electrical
& Electronics Engineering from Sree
Kavitha Engineering college, Karepally, Khammam, A.P.
And then completed her P.G in Electrical & Electronics
Engineering, specialization in Power Electronics at
MOTHER THERESA Institute of Science & Technology,
Sathupally, Khammam, A.P, She has a teaching experience
of 6 years. She did project on Power project implement using
modified UPQC topology with reduced DC link voltage
systems. Her areas of interest are Power Systems, Power
Electronics, and Electrical Machines.
International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0559-0565