Modeling Analysis& Solution of Power Quality Problems Using DVR & DSTATCOM

IJSRD - International Journal for Scientific Research & Development| Vol. 1, Issue 5, 2013 | ISSN (online): 2321-0613
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Abstract— A Power quality problem is an occurrence
manifested as a nonstandard voltage, current or frequency
that results in a failure or a disoperation of end use
equipment. Utility distribution networks,
sensitive industrial loads, and critical commercial
operations all suffer from various types of outages and
service interruptions which can cost significant financial
loss per incident based on process down-time, lost
production, idle work forces, and other factors. With
the restructuring of Power Systems and with shifting trend
towards Distributed and Dispersed Generation, the issue of
Power Quality is going to take newer dimensions. The aim
therefore, in this work, is to identify the prominent concerns
in the area and thereby to recommend measures that can
enhance the quality of the power, keeping in mind their
economic viability and technical repercussions. In this paper
electromagnetic transient studies are presented for the
following two custom power controllers: the distribution
static compensator (DSTATCOM), and the dynamic voltage
restorer (DVR). Comprehensive results are presented to
assess the performance of each device as a potential custom
power solution.
Keywords: Power Quality Problems, Power System
Restructuring, Voltage Sag, DSTATCOM, DVR,
MATLAB. I.
I. INTRODUCTION
Power quality is certainly a major concern in the present era;
it becomes especially important with the introduction of
sophisticated devices, whose performance is very sensitive
to the quality of power supply. Modern industrial processes
are based a large amount of electronic devices such as
programmable logic controllers and adjustable speed drives.
The electronic devices are very sensitive to disturbances [1]
and thus industrial loads become less tolerant to power
quality Problems such as voltage dips, voltage swells, and
harmonics. Voltage dips are considered one of the most
severe disturbances to the industrial equipment. A paper
machine can be affected by disturbances of 10% voltage
drop lasting for 100ms. A voltage dip of 75% (of the
nominal voltage) with duration shorter than 100ms can
result in material loss in the range of thousands of US
dollars for the semiconductors industry [2]. Swells and over
voltages can cause over heating tripping or even destruction
of industrial equipment such as motor drives. Electronic
equipment is very sensitive loads against harmonics because
their control depends on either the peak value or the zero
crossing of the supplied voltage, which are all influenced by
the harmonic distortion.
This paper analyzes the key issues in the Power Quality
problems, specially keeping in mind the present trend
towards more localized generations (also termed as
distributed and dispersed generation) and consequent
restructuring of power transmission and distribution
networks. As one of the prominent power quality problems,
the origin, consequences and mitigation techniques of
voltage sag problem has been discussed in detail. The study
describes the techniques of correcting the supply voltage sag
in a distribution system by two power electronics based
devices called Dynamic Voltage Restorer (DVR) and
Distribution STATCOM (DSTATCOM).A DVR voltage in
series with the system voltage and a DSTATCOM injects a
current into the system to correct the voltage sag [1]. The
steady state performance of both DVR and DSTATCOM is
studied for various levels of voltage sag levels.
II. SOURCES AND EFFECTS OF POWER QUALITY PROBLEMS
The distortion in the quality of supply power can be
introduced /enhanced at various stages; however, some of
the primary sources of distortion [3] can be identified as
below:
1 Power Electronic Devices
2 IT and Office Equipment
3 Arcing Devices
4 Load Switching
5 Large Motor Starting
6 Embedded Generation
7 Electromagnetic Radiations and Cables
8 Storm and Environment Related Causes etc.
While power disturbances occur on all electrical systems,
the sensitivity of today’s sophisticated electronic devices
makes them more susceptible to the quality of power supply.
For some sensitive devices, a momentary disturbance can
cause scrambled data, interrupted communications, a frozen
mouse, system crashes and equipment failure etc. A power
voltage spike can damage valuable components. Some of the
common power quality issues and their prominent impact
are summarized in the table 1
III. SOLUTIONS TO POWER QUALITY PROBLEMS
There are two approaches to the mitigation of power quality
problems. The solution to the power quality can be done
from customer side or from utility side [4]. First approach is
called load conditioning, which ensures that the equipment
is less sensitive to power disturbances, allowing the
operation even under significant voltage distortion. The
other solution is to install line conditioning systems that
suppress or counteracts the power system disturbances. A
flexible and versatile solution to voltage quality problems is
offered by active power filters. Currently they are based on
PWM converters and connect to low and medium voltage
Modeling Analysis& Solution of Power Quality
Problems Using DVR & DSTATCOM
Janak B. Patel1
Amitkumar Singh2
1
M.Tech 2
Asst. Professor
1,2
Sobhasaria Group of Institution, Sikar
S.P.B.Patel Engineering College, Mehsana, Gujarat

Modeling Analysis& Solution of Power Quality Problems Using DVR & DSTATCOM
(IJSRD/Vol. 1/Issue 5/2013/045)
Distribution system in shunt or in series
Problem Effects
Voltage Sags Devices/Process downtime, Effect on product
quality, Failure/Malfunction of customer
equipment(such as tripping of large industrial
drives) and associated scrap cost, cleanup
costs, maintenance and repair costs etc.
Transients Tripping, Component failures, flashover of
instrument insulation, hardware rebooting,
software problems, poor product quality etc.
Harmonics Excessive losses and heating in motors,
capacitors and transformers connected to the
system, Insulation failure due to overheating
and over voltages, loss of conductor life and
possible risk of fire due to overheating,
malfunctioning of sophisticated electronic
equipment, higher electric stress and harmonic
resonance, saturation in transformer cores,
Interference with adjacent communication
networks, audio hum, video fluster, power
supply failure etc.
Flickers Visual ionization, Introduction of many
harmonic components in the supply power and
their associated ill effects.
Table 1: Various Power Quality Problems and Their Effects
Series active power filters must operate in conjunction with
shunt passive filters in order to compensate load current
harmonics. Shunt active power filters operate as a
controllable current source and series active power filters
operates as a controllable voltage source. Both schemes are
implemented preferable with voltage source PWM inverter s
[5], with a dc bus having a reactive element such as a
capacitor. Active power filters can perform one or more of
the functions required to compensate power systems and
improving power quality. Their performance also depends
on the power rating and the speed of response.
However, with the restructuring of power sector and with
shifting trend towards distributed and dispersed generation,
the line conditioning systems or utility side solutions will
play a major role in improving the inherent supply quality;
some of the effective and economic measures can be
identified as following:
A. Lightening and Surge Arresters:
Arresters are designed for lightening protection of
transformers, but are not sufficiently voltage limiting for
protecting sensitive electronic control circuits from voltage
surges.
B. Thyristor Based Static Switches
The static switch is a versatile device for switching a new
element into the circuit when the voltage support is needed.
It has a dynamic response time of about one cycle. To
correct quickly for voltage spikes, sags or interruptions, the
static switch can used to switch one or more of devices such
as capacitor, filter, alternate power line, energy storage
systems etc. The static switch can be used in the alternate
power line applications. This scheme requires two
independent power lines from the utility or could be from
utility and localized power generation like those in case of
distributed generating systems [4]. Such a scheme can
protect up to about 85 % of interruptions and voltage sags.
C. Energy Storage Systems:
Storage systems can be used to protect sensitive
production equipments from shutdowns caused by voltage
sags or momentary interruptions. These are usually DC
storage systems such as UPS, batteries, superconducting
magnet energy storage (SMES), storage capacitors or even
fly wheels driving DC generators [6]. The output of these
devices can be supplied to the system through an inverter on
a momentary basis by a fast acting electronic switch.
Enough energy is fed to the system to compensate for the
energy that would be lost by the voltage sag or interruption.
In case of utility supply backed by a localized generation
this can be even better accomplished.
D. Electronic tap changing transformer:
A voltage-regulating transformer with an electronic
load tap changer can be used with a single line from the
utility. It can regulate the voltage drops up to 50% and
requires a stiff system (short circuit power to load ratio of
10:1 or Better). It can have the provision of coarse or
smooth steps intended for occasional voltage variations.
E. Harmonic Filters:
Filters are used in some instances to effectively reduce or
eliminate certain harmonics [7]. If possible, it is always
Preferable to use a 12-pluse or higher transformer
connection, rather than a filter. Tuned harmonic filters
should be used with caution and avoided when possible.
Usually, multiple filters are needed, each tuned to a separate
harmonic. Each filter causes a parallel resonance as well as a
series resonance, and each filter slightly changes the
resonances of other filters.
F. Constant-Voltage Transformers:
For many power quality studies, it is possible to greatly
improve the sag and momentary interruption tolerance of a
facility by protecting control circuits. Constant voltage
transformer (CVTs) can be used [6] on control circuits to
Provide constant voltage with three cycle ride through, or
relays and ac contactors can be provided with electronic coil
hold-in devices to prevent disoperation from either low or
interrupted voltage.
G. Digital-Electronic and Intelligent Controllers for Load-
Frequency Control:
Frequency of the supply power is one of the major
determinants of power quality, which affects the equipment
performance very drastically. Even the major system
components such as Turbine life and interconnected-grid
control are directly affected by power frequency. Load
frequency controller used specifically for governing power
frequency under varying loads must be fast enough to make
adjustments against any deviation. In countries like India
and other countries of developing world, still use the
controllers which are based either or mechanical or

electrical devices with inherent dead time and delays and at
times also suffer from ageing and associated effects. In
future perspective, such controllers can be replaced by their
Digital-electronic counterparts.
IV. USES OF CUSTOM POWER DEVICES TO IMPROVE POWER
QUALITY
In order to overcome the problems such as the ones
mentioned above, the concept of custom power devices is
introduced recently; custom power is a strategy, which is
designed primarily to meet the requirements of industrial
and commercial customer. The concept of custom power is
to use power electronic or static controllers in the medium
voltage distribution system aiming to supply reliable and
high quality power to sensitive users [1].Power electronic
valves are the basis of those custom power devices such as
the static transfer switch, active filters and converter-based
devices. Converter based power electronics devices can be
divided in to two groups: shunt-connected and series-
connected devices. The shunt connected devices is known as
the DSTATCOM and the series device is known as the
Static Series Compensator (SSC), commercially known as
DVR. It has also been reported in literature that both the
SSC and DSTATCOM have been used to mitigate the
majority the power system disturbances such as voltage
dips, sags, flicker unbalance and harmonics. For lower
voltage sags, the load voltage magnitude can be corrected by
injecting only reactive power into the system. However, for
higher voltage sags, injection of active power, in addition to
reactive power, is essential to correct the voltage magnitude
[8]. Both DVR and DSTATCOM are capable of generating
or absorbing reactive power but the active power injection
of the device must be provided by an external energy source
or energy storage system. The response time of both DVR
and DSTATCOM is very short and is limited by the power
electronics devices. The expected response time is about25
ms, and which is much less than some of the traditional
methods of voltage correction such as tap changing
transformers. V. Modeling of Custom Power Devices and
Simulation Results As mentioned in the previous section
that custom power devices could be the effective means to
overcome some of the major power quality problems by the
way of injecting active and/or reactive power(s) into the
system [9]-[11].This section of the paper deals with the
modeling of DSTATCOM and DVR. Consequently some
case studies will be taken up for analysis and performance
comparison of these devices. The modeling approach
adopted in the paper is graphical in nature, as opposed to
mathematical models embedded in code using a high-level
computer language. The well-developed graphic facilities
available in an industry standard power system package,
namely, MATLAB (/Simulink) [12], is used to conduct all
aspects of model implementation and to carry out extensive
simulation studies. The control scheme for these devices is
shown in Fig.1.The controller input is an error signal
obtained from the reference voltage and the value r.m.s of
the terminal voltage measured. Such error is processed by a
PI controller and the output is the angle d, which is provided
to the PWM signal generator. The PWM generator then
generates the pulse signals to the IGBT gates of voltage
source converter [10].
Fig.1: the PI Controller
A. DSTATCOM
The test system employed to carry out the simulations
concerning the DSTATCOM actuation for voltage sag
compensation is shown in Fig.2. Such system is composed
by a 230 kV, 50 Hz transmission system, represented by a
Thevenin equivalent, feeding a distribution network through
a 3-winding transformer connected in Y/Y/Y, 230/11/11 kV.
To verify the working of a DSTATCOM, a variable load is
connected at bus 2. During the simulation, in the period
from 500 to 900 ms, the switch S1 is closed .The above test
system is simulated under the environment of Matlab -
Simulink and power system block set (PSB) the model used
for this purpose is shown in the Fig.3.
Fig. 2 Test system for DSTATCOM
Fig. 3: MATLAB Simulation model of DSTATCOM

Fig. 4: Voltage response of the test system without
DSTATCOM (Single Line-to-ground Fault, RL load)
Fig.4. shows the r.m.s voltage at the load point with RL load
for the case when the system operates with no DSTATCOM
and if the single line to ground fault is created during the
period of 500ms to 900 ms via 0.2 Ω resistance. Similarly, a
new set of simulations was carried out but now with the
DSTATCOM connected to the system. The results are
shown in Fig.5. Where the very effective voltage regulation
provided by the DSTATCOM can be clearly appreciated.
Fig. 5: Voltage response of the test system with
DSTATCOM (Single Line-to-ground Fault, RL load)
The second simulation contains no DSTATCOM and three
phase capacitive load applied during the period 500-900ms.
The voltage swell at the load point is 40% with respect to
the reference voltage is shown in Fig. 6 and the test system
for the simulation of DSTATCOM for swell is shown in
figure 3.For this condition if we connect the DSTATCOM
than the voltage if improve near about reference voltage
which is shown in Fig. 7.
Fig. 6: Voltage response of the test system without
DSTATCOM with RC load
Fig. 7: Voltage response of the test system with
DSTATCOM with RC load
B. DVR
The test system employed to carry out the simulations
concerning the DVR actuation is shown in Fig. 8. Such
Network is composed by a 13 kV, 50 Hz generation system,
represented by a Thevenin equivalent, feeding two
Transmission lines through an 3-winding transformer
connected in Y/? /? 13/115 /115 kV. Such transmission
lines feed two distribution networks through two
transformers connected in? /Y, 115/11 kV. To verify the
working of a DVR employed to avoid voltage sags during
short-circuit, a fault is applied at point X via a resistance of
0.2 O. Such fault is applied from 500 to 900 ms.
Fig. 8: Test system for DVR
The above test system is simulated under the environment of
Matlab-Simulink and power system block set (PSB) the
Model used for this purpose is shown in the Fig.9.
Four simulations studies are carried out as follows:
1 The first simulation contains no DVR and a Single –
phase short-circuit fault is applied at point A, via a fault
resistance of 0.2? , during the period 500–900 ms. The
voltage sag at the RC load point is almost 40% with
respect to the reference voltage.
2 The second simulation is carried out using the same
scenario as above but now with the DVR in operation.
The Total simulation period is 1.0 s.
3 The third simulation contains no DVR and a three –
phase short-circuit fault is applied at point A, via a fault
resistance of 0.001? , during the period 500–900 ms.
The voltage sag at the load point is almost 0% with
respect to the reference voltage.

4 The fourth simulation is carried out using the same
scenario as above but now with the DVR in operation.
The Total simulation period is 1.0 s.
Using the facilities available in MATLAB the DVR is
simulated to be in operation only for the duration of the
fault, as it is expected to be the case in a practical situation.
The results for all simulations are shown in Fig.10, 11, 12
and Fig.13. Voltage response without DVR is shown in
Fig.10 and Fig.12 for single phase and three phase to ground
fault. Voltage response with DVR is shown in Fig 11 and
Fig 13 for both fault condition.
The PWM control scheme controls the magnitude and the
phase of the injected voltages, restoring the r.m.s voltage
very effectively [13]-[14]. The sag mitigation is performed
with a smooth, stable, and rapid DVR response.
Fig. 9: MATLAB Simulation model of DVR
Fig. 10: Single Line-to-ground Fault without DVR
Fig. 11: Single Line-to-ground Fault without DVR
Fig.12.Three Phase-to-ground Fault without DVR
Fig. 13: Three Phase-to-ground Faults with DVR
V. CONCLUSIONS
Power quality measures can be applied both at the user end
and also at the utility level. The work identifies some
important measures that can be applied at the utility level
without much system upset (or design changes).This paper
has presented models of custom power equipment, namely
DSTATCOM, DVR, and applied them to mitigate voltage
dip which is very prominent as per utilities are concerned.
The highly developed graphic facilities available in
MATLAB SIMULINK were used to conduct all aspects of
model implementation and to carry out extensive simulation
studies on test systems. A new PWM-based control scheme
has been implemented to control the electronic valves in the
two level VSC used in the DSTATCOM and DVR.As
opposed to fundamental frequency switching schemes
already available in the MATLAB- SIMULINK. This
characteristic makes it ideally suitable for low-voltage
custom power applications. It was observed that in case of
DSTATCOM capacity for power compensation and voltage
regulation depends mainly on the rating of the dc storage
device. The simulation results presented shows good
accuracy with results reported in index journals.
ACKNOWLEDGMENT
I must acknowledge the strength, energy and patience that
almighty GOD bestowed upon me to start & accomplish this
work with the support of all concerned, a few of them I am
trying to name hereunder.
I would like to express my deep sense of gratitude to my
guide Prof. Amit kumar Singh (HOD, EED, Shobhasaria
Engg. College, SIKAR) for his valuable guidance and
motivation and for his extreme cooperation to complete my
work successfully
I am indebted Prof. Amit kumar Singh (HOD, EED,
Shobhasaria Engg. College, SIKAR),PG In charge of

Electrical Engineering Department, for his consent and
permission to utilize the facilities of the department for my
study.
I appreciate all my colleagues whose direct and indirect
contribution helped me a lot to accomplish this work. No
words are adequate to express my indebtedness to my
parents for their blessings and good wishes. To them I bow
in the deepest reverence.
REFERENCES
[1] H. Hingorani,” Introducing custom power”, IEEE
spectrum, vol.32 no.6 June 1995 p 41-48.
[3] John Stones and Alan Collinsion, “Introduction to
Power Quality”, Power Engineering Journal 2001
pages: 58 -64.
[4] Gregory F. Reed, Masatoshi Takeeda, “Improved
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[5] G. Venkataramanan and B. Johnson, “A pulse width
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[6] N.G. Hingorani and L. Gyugyi, “Understanding
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[8] F. Z. Peng, H. Akagi, and A. Nabae, “Compensation
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Sept. 2001 Pages:5 pp. vol.1
[10] S. S. Choi, B. H. Li and D. D.Vilathgamuwa,
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[11] O. Anaya-Lara, E. Acha, “Modeling and Analysis of
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[12] P.W. Lehn and MR. Iravani, “Experimental
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[13] TEQSIM International Inc., Power System Blocks et
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Electronics: Converters, Applications and Design”,
New York: Wiley, 1995

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