Simulation and Modeling of Dynamic Voltage Restorer for Compensation Of Voltage Sag and Voltage Swell

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 1 | Jan -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 100
SIMULATION AND MODELING OF DYNAMIC VOLTAGE RESTORER FOR
COMPENSATION OF VOLTAGE SAG AND VOLTAGE SWELL
Sangita R. Kamble1, Khusbhu Patil2
M-Tech Student, Power Electronics and Power System, W.C.E.M, Nagpur (M.H), India1
Asst. Professor, Power Electronics and Power System, W.C.E.M, Nagpur (M.H), India2
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Abstract: Power Quality problem in a system leads to various
disturbances such as voltage fluctuations, transients and
waveform distortions that results in a mis-operation or a
failure of end user equipment. There are different types of
custom power devices likeDistributionStaticCompensator(D-
STATCOM) and Dynamic Voltage Restorer (DVR) which can
effectively use for mitigation of different type of power quality
problems. This paper describes the technique ofcorrectingthe
supply voltage sag and swell distributed system.DVRbased on
VSI principle. A DVR is a series compensation device which
injects a voltage in series with which injects a current into the
system to correct the power quality problems. This paper
presents a power system operation with PI controllerwith abc
to dq0 convertor approach. Results are presentedtoassessthe
performance of devices as a potential custom power solution.
Improve dynamic voltage control and thus increase system
load ability. This paper presents modeling and simulation of
DVR in MATLAB/Simulink.
Key Words: Voltagesag,Voltageswells,Park transformation,
DVR, MATLAB/Simulink.
1. INTRODUCTION
The electric power system is considered to be
composed of three functional blocks - generation,
transmission and distribution. For a reliable power system,
the generation unit must produce adequate power to meet
customer’s demand, transmission systems must transport
bulk power over long distances without overloading and
distribution systems must deliver electric power to each
customer’s premises from bulk power systems. Distribution
system locates the end of power system and is connected to
the customer directly, so the power quality mainly depends
on distribution system. With the advent of myriad
sophisticated electrical and electronic equipment, such as
computers, programmable logic controllers and variable
speed drives which are very sensitive to disturbances and
non-linear loads at distribution systems produces many
power quality problems like voltage sags, swells and
harmonics and the purity of sine waveform is lost. [1][2]
Voltage sags are considered to be one of the most severe
disturbances to the industrial equipment’s.
Power distribution systems, ideally, shouldprovide
their customer with an uninterrupted power flow at smooth
sinusoidal voltage at the contracted magnitude level and
frequency .A momentary disturbanceforsensitive electronic
devices causes voltage reduction at load end leading to
frequency deviations which results in interrupted power
flow, scrambled data, unexpected plant shutdowns and
equipment failure. Voltage lift up at a load can be achieved
by reactive power injection at the load point of common
coupling (PCC).
The common method for this is to install
mechanically switched shunt capacitors in the primary
terminal of the distribution transformer. The mechanical
switching may be on a schedule, via signals from a
supervisory control and data acquisition (SCADA) system,
with some timing schedule, or with no switching at all. The
disadvantage is that, high speed transients cannot be
compensated. Some sag is not corrected within the limited
time frame of mechanical switching devices. Transformer
taps may be used, but tap changing under load is costly.
Another power electronic solution to the
voltage regulation is the use of a dynamic voltage
restorer (DVR). DVR’s are a class of custom power
devices for providing reliable distribution power
quality. They employ a series of voltage boost
technology usingsolidstateswitchesforcompensating
voltage sags. The DVR applications are mainly for
sensitive loads that may be drastically affected by
fluctuations in system voltage.
2. CONVENTIONAL SYSTEM CONFIGURATION
OF DVR
Dynamic Voltage Restorer is a series
connected device designed to maintain a constant
RMS voltage value across a sensitive load. The DVR
considered consists of:
a. an injection / series transformer
b. a harmonic filter,
c. a Voltage Source Converter (VSC)
d. an energy storage and
e. a control system , as shown in Figure

Figure 1: Schematic diagram of DVR
3. CONTROLLER ALGORITHM
The aim of the control scheme is to maintain
constant voltage magnitude at the point where a sensitive
load is connected, under system disturbances. The control
system only measures the r.m.s voltage at the load point i.e.
no reactive power measurements are required. The VSI
switching strategy is basedona PWMtechniquewhichoffers
simplicity and good response also PWM is used to vary the
amplitude and the phase angle of the injected voltage. Since
custom power is a relatively low-power application, PWM
methods offer a more flexible option than the Fundamental
Frequency Switching (FFS) methods favored in FACTS
applications. Besides,highswitchingfrequenciescanbe used
to improve on the efficiency of the converter, without
incurring significant switching losses.
There are several ways to control the DVR. Different partsof
the controls include.
• identify the occurrence of sag / swell in the system.
• Calculate the offset voltage.
• Pulse output of the PWM inverter fire and stop it whenthe
problem is resolved.
In normal and synchronous conditions, the voltage
is a constant, d-voltage is one pu and q-voltage unit is zero
pu, but in normal circumstances can be a change. The d-
voltage and q-voltage with the interest that needed for best
performance is compared then the d and q error is
generated. Thus the d-q contents of error become abc
content. Choose to provide dq0 method, give information
about the size (d), phase shift (q) with start and end voltage
fallen leaves. Load voltages base on the Park
transformations, and according to the following equation
becomes.
……(1)
Where the angle between the
rotating and fixed coordinate system at each is time t
and is an initial phase shift of the voltage.
And according inverse Parks Transformation
………(2)
As in the Clarke Transform, it is interesting to
note that the 0-component above is the same as the
zero sequence component in the symmetrical
components transform. For example, for voltages Ua,
Ub and Uc, the zero sequence component for both the
dq0 and symmetrical components transforms
is .
Main voltages used as a Phase lock loop (PLL)
to generate sine-wave single phase. The contents are
used for production abc three phases PWM pulses.
Control technique employed throughout this paper is
shown below in Figure
Figure 2 Schematic diagrams of control block.
4. DYNAMIC VOLTAGE RESTORER
Among the power quality problems like sag,
swell, harmonic etc, voltage sag is the most severe
disturbances in the distribution system. To overcome
these problems the concept of custom power devices
is introduced lately. One of those devices is the
Dynamic Voltage Restorer (DVR), which is the most
efficient and effective modern custom power device
used in power distribution networks.

DVR is a recently proposed series connected
solid state device that injects voltage into the system
in order to regulate the load side voltage. It is
generally installed in a distribution system between
the supply and the critical load feeder at the point of
common coupling (PCC). Other than voltage sags and
swells compensation, DVR can also added other
features like line voltage harmonics compensation,
reduction of transients in voltage and fault current
limitations.
Figure 3 DVR series connected topology
The compensation for voltage sags using a DVR can
be performed by injecting/absorbing reactive power or real
power. When the injected voltage is in quadrature with the
current at the fundamental frequency, compensation is
achieved by injecting reactive power and the DVR itself is
capable of generating the reactive power because DVR is
self-supported with dc bus. But, DVR voltage can be kept in
quadrature with the current only up to a certain value of
voltage sag and beyond which the quadrature relationship
cannot be maintained to correct the voltage sag i.e. if the
injected voltage is in phase with the current,DVR injectsreal
power and hence an energy storage device is required at the
dc side of VSI. The control technique adopted should
consider the limitations such as the voltage injection
capability (inverter and transformer rating) and
optimization of the size of energy storage.
1 .Parameter table
5. SIMULATION RESULTS AND DISCUSSION
5.1 SIMULINK MODEL OF THE DVR TEST
SYSTEM IN STEADY STATE AND TRANSIENT
CONDITIONS
In this simulink model we have a system in
which two parallel feeders are shown. In both the
feeders further loads are also connected in parallel.
In one feeder DVR is connected in series with line
and the other feeder is kept as it is. Here system is
presented without DVR and fault.
Sr.
no.
System
quantities
Standards
1. Main Supply
Voltage per
phase
440V
2. Line
Impedance
Ls =1 mH
Rs = 0.5 Ω
3. Linear/Isolation
transformer
1:1 turns ratio,
440/440 V
4. DC Bus
Voltage
135 V
5. Load
resistance
5 Ω
6. Inverter IGBT based,3
arms,
6 Pulse,
Carrier
Frequency
=1000 Hz,
Sample Time= 5
μs
7. Load
inductance
1 mH
8. Line
Frequency
50Hz

Figu
re 4 simulink model of the DVR test system in steady
state conditions
Result for the above system in which without DVR and
fault is given below. The output voltageforsourceside,
load 1 and load 2 is same. The wave shapes in figure-
5.8 represent source voltage, load 1 and load 2 with
respect to time.
Figure 5 Waveform in Steady state condition
A detailed system as shown in Figure 8 has
been modeled by MATLAB/SIMULINK to study the
efficiency of suggested control strategy. The system
parameters and constant value arelisted inTableI.Itis
assumed that the voltage magnitude of the load bus is
maintained at 1 pu during the voltage sags/swells
condition. The results of the most important
simulations are represented in Figures 6-7.
Voltage Sag
The first simulation shows of three phase
voltage sag are simulated. The simulation started
with the supply voltage 50% sagging as shown in
Figure 6 (a).In Figure 6 (a) also shows a 50% voltage
sag initiated at 0.15s and it is kept until 0.35s, with
total voltage sag duration of 0.2s. Figures 5 (b) and
(c) show the voltage injected by the DVR and The
corresponding load voltage with compensation.
Figure 7 Three-phase voltages swell: (a)-Source
voltage, (b)-Injected voltage, (c)-Load voltage
Figure 6 Three-phase voltages sag: (a)-Source
voltage, (b)-Injected voltage,(c)-Load

Voltage Swell
The second simulation shows the DVR performance
during a voltage swell condition. The simulation
started with the supply voltage swell is generated as
shown in Figure 7 (a). As observed from this figure the
amplitude of supply voltage is increased about 25%
from its nominal voltage. Figures 7(b)and(c)showthe
injected and the load voltage respectively. As can be
seen from the results, the load voltage is kept at the
nominal value with the help of the DVR. Similar to the
case of voltage sag, the DVR reacts quickly to inject the
appropriate voltage component to correct the supply
voltage.
6. CONCLUSION
The modeling and simulation of a DVR using
MATLAB/SIMULINK has been presented. A control
system based on dqo technique which is a scaled error
of the between source side of the DVRanditsreference
for sags/swell correction has been presented. The
simulation shows that the DVR performance is
satisfactory in mitigating voltage sags/swells.

Simulation and Modeling of Dynamic Voltage Restorer for Compensation Of Voltage Sag and Voltage Swell

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