Download International Electrical Engineering Journal (IEEJ) Vol. 5 (2014) No.12, pp. 1649-1654

International Electrical Engineering Journal (IEEJ)
Vol. 5 (2014) No.12, pp. 1649-1654
ISSN 2078-2365
http://www.ieejournal.com/
Implementation of SPWM Technique in
D-STATCOM for Voltage Sag and Swell
David Vorganti1, Cholleti Sriram2
david.gnit24@gmail.com, cholletisriram6@gmail.com

Abstract— This paper presents the implementation of
Sinusoidal Pulse width modulation (SPWM) technique to
control Voltage Source Controller (VSC) in Distribution
STATCOM (D-STATCOM) to mitigate power quality
problems, voltage sag and swell. Power quality determines the
fitness
of electrical
power
to
consumer
devices.
Synchronization of the voltage frequency and phase
allows electrical systems to function in their intended manner
without significant loss of performance or life. The major
problems in distribution system are the voltage sag and swell.
To solve this problem, modern power electronic devices are
used. One of those devices is the Distribution STATCOM (DSTATCOM), which is the most efficient and effective FACTS
based modern power device used in power distribution
networks. D-STATCOM injects a current in to the system to
correct the voltage sag and swell. The control of the Voltage
Source Converter (VSC) is done with the help of SPWM. The
proposed and implementation of SPWM in VSC of DSTATCOM
is
designed
and
simulated
using
MATLAB/SIMULINK software.
Index Terms— Dynamic Analysis, DSP-Based Control,
Hybrid Stepping Motor
TSC, TSR, SSSC and etc. The reactive power at the terminals
of the STATCOM depends on the amplitude of the voltage
source, these FACTS devices employ a shunt of voltage
boost
technology using
solid
state switches for
compensating voltage
sags and swells.
And these
STATCOM in distribution system is called DSTACOM
(Distribution-STACOM).
Distribution STATCOM (D-STATCOM) exhibits high
speed and control reactive power, to give voltage
stabilization flicker suppression. A DSTATCOM is a
controlled reactive source which includes a Voltage Source
converter (VSC) and a DC link capacitor connected in shunt,
capable of generating and /or absorbing reactive power [4].
Voltage support at a load can be achieved by reactive power
injection at the load point of common coupling.
D-STATCOM injects a current into the system to correct the
voltage “flickers” and improve power quality problem with
the help of MATLAB SIMULINK software. The D
STATCOM applications are mainly for sensitive loads that
may be drastically affected by fluctuations in the system
II. POWER QUALITY PROBLEMS
I. INTRODUCTION
Electrical power is perhaps the most essential raw material
used by commerce and industry today. In recent years, there
has been an increased emphasis and concern for the quality of
power delivered to factories, commercial establishments and
residences [1]. The most common problem in power quality
today is voltage sag & swells. All modern industrial devices
are mostly based on the Power electronic devices. The
electronic devices are very sensitive to disturbances and
become less tolerant to power quality problems [2] such as
voltage sags, swells and harmonics. Voltage dips are
considered to be one of the most severe disturbances to the
industrial equipments [3].
The FACTS devices are introduced to electrical system to
improve the power quality of the electrical power. Use of
these FACTS controllers to enable corresponding power to
flow through such line under normal and abnormal
conditions there are different type of FACTS device DVR,
STATCOM, DSTATCOM, UPQC, UPFC, SVC, SSG, TCR,
A. Overview
Electric Power quality is a term which has captured
increasing attention in power engineering in the recent years.
The term power quality refers to maintaining a sinusoidal
waveform of bus voltages at rated voltage and frequency.
Power quality areas may be made according to the source of
the problem such as converters, magnetic circuit non linearity
by the wave shape of the signal such as harmonics, flicker or
by the frequency spectrum (radio frequency interference).
Power quality is simply the interaction of electrical power
with electrical equipment. Power quality is the cause, and the
ability of the electrical equipment to function in the power
quality environment is the effect. Various sources use the
term “power quality” with different meaning. It is used
synonymously with “supply reliability,” “service quality,”
“voltage quality,” “current quality,” “quality of supply” and
“quality of consumption [5]. A power voltage spike can
damage valuable components. Power quality problems
encompass a wide range of disturbances such as voltage sags,
swells, flickers, harmonic distortion, impulse transients, and
interruptions.
1649
David and Cholleti
Implementation of SPWM Technique in DSTATCOM for Voltage Sag and Swell
International Electrical Engineering Journal (IEEJ)
Vol. 5 (2014) No.12, pp. 1649-1654
ISSN 2078-2365
http://www.ieejournal.com/
B. Sources of Power Quality Problems
Power quality problems have many name and
descriptions. Surges, spikes, transient’s blackouts, noise,
voltage sag, voltage swell, interruption, dc offset are some
common descriptions.
The percentage of power quality problems are figured below.
C. Causes of Voltage Sags and Swells




Rural location remote from power source
Unbalanced load on a three phase system
Switching of heavy loads
Long distance from a distribution transformer with
interposed loads
 Unreliable grid systems
 Equipments not suitable for local supply.
D. Solution to Power Quality Problems
There are two approaches to mitigate the power quality
problems. The solution to the power quality can be done from
customer side or from utility side; 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 counteract
the power system disturbances. Currently they are based on
PWM converters and connect to low and medium voltage
distribution system in shunt or in series. 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 operate as a controllable voltage
David and Cholleti
source. Both schemes are implemented in preferable with
voltage source PWM inverters, with a dc bus having a
reactive element such as a capacitor. 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 [5]
1) Lightning and Surge Arrester: Arrester is designed for
lightning protection of transformers, but is not limited to
sufficient voltage limiting for protecting sensitive electronic
control circuits from voltage surges.
2) Thyristor Based Static Switch: The static switch is a
versatile device for switching a new element in to 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 devises such as capacitor, filter,
alternate power line, energy storage systems etc. The static
switch can be used in the alternate power line applications.
3) Energy Storage Systems: Storage system can be used to
protect sensitive protection equipment 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. 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.
III. METHODOLOGY
A. Distributed Static Compensator(DSTATCOM)
D-STATCOM is the most important controller for
distribution networks. It has widely used to regulate system
voltage, improve voltage profile, reduce voltage harmonics,
reduce transient voltage disturbances and load compensation.
The DSTATCOM uses a power–electronics converter is
controlled using pulse width modulation (PWM).
Schematically single line diagram is depicted in Fig.3.1
consists of a two level self-commutated Voltage source
converter (VSC), a dc energy storage device, a coupling
transformer connected in shunt to the distribution network
through a coupling transformer. Such configuration allows
the device to absorb or generate controllable active and
reactive power. The D-STATCOM has been utilized mainly
for regulation of voltage, correction of power factor and
elimination of current harmonics. Such a device is employed
to provide continuous voltage regulation using an indirectly
controlled converter. In this paper, the D-STATCOM is used
to regulate the voltage at the point of connection. The control
is based on sinusoidal PWM and only requires the
measurement of the rms voltage at the load point.
1650
Implementation of SPWM Technique in DSTATCOM for Voltage Sag and Swell
International Electrical Engineering Journal (IEEJ)
Vol. 5 (2014) No.12, pp. 1649-1654
ISSN 2078-2365
http://www.ieejournal.com/
The Distribution Static Compensator (D- STATCOM) is a
voltage source inverter based static compensator that is used
for the correction of bus voltage sags.
Fig. 1 Basic structure of D-STATCOM
The major components of a D-STATCOM are shown in
Fig.3.1. It consists of a source, DC link capacitor, one or
more inverter modules, an ac filter, a transformer to match
the inverter output to the line voltage, and a PWM control
strategy [8].
B. Equations Related to D-STATCOM
The shunt injected current Ish corrects the voltage sag by
adjusting the voltage drop across the system impedance Zth.
The value of Ish can be controlled by adjusting the output
voltage of the converter. The shunt injected current Ish can be
written as,
current Ish is kept in quadrature with VL, the desired voltage
correction can be achieved without injecting any active
power into the system. On the other hand, when the value of
Ish is minimized, the same voltage correction can be achieved
with minimum apparent power injection into the system.
C. Three Phase Voltage Source Converter (VSC)
VSC is heart of most new FACTS power equipments.
Voltage source converters (VSC) are commonly used to
transfer power between a dc system and an ac system or back
to back connection for ac systems with different frequencies
.A voltage source converter (VSC) is a power electronic
device, which can generate a three-phase ac output voltage is
controllable in phase and magnitude [1]. These voltages are
injected into the ac distribution system in order to maintain
the load voltage at the desired voltage reference. VSCs are
widely used in adjustable speed drives, but can also be used
to mitigate the voltage sags and swells. The VSC is used to
either completely replacing the voltage or to inject the
'missing voltage'. The 'missing voltage' is the difference
between the nominal voltage and the actual voltage. The
converter is normally based on the some kind of energy
storage, which will supply the converter with a dc voltage. A
basic VSC structure is shown in (Figure.3.7) where Rs and Ls
represent the resistance and inductance between the converter
ac voltages V and the ac system voltage Vs and Is the current
injected into the grid. A dc capacitor is connected on the dc
side to produce a smooth dc voltage. The IGBTs are
connected anti parallel with diodes for commutation purposes
and charging of the DC capacitor [9].
Here source current is
Therefore the injected shunt current is given by
In Polar form
The complex power injection of the D-STATCOM can be
expressed as,
Where,
Fig.2 Sinusoidal PWM based Control
Iout = Output current,
I L = Load current,
Is = Source current,
VL = Load voltage,
Vth = Thevenin voltage,
Zth = Impedance (Zth=R+jX)
It may be mentioned that the effectiveness of the DSTATCOM in correcting voltage sag depends on the value of
Zth or fault level of the load bus. When the shunt injected
The aim of the control scheme is to maintain constant
voltage magnitude at the point where a sensitive load is
connected, under system disturbance. The control system
only measures the rms voltage at the load point i.e., no
reactive power measurements are required [10]. The VSC
switching (4)(5) strategy is based on sinusoidal PWM
technique which offers simplicity and good response. The PI
1651
David and Cholleti
Implementation of SPWM Technique in DSTATCOM for Voltage Sag and Swell
International Electrical Engineering Journal (IEEJ)
Vol. 5 (2014) No.12, pp. 1649-1654
ISSN 2078-2365
http://www.ieejournal.com/
controller process identifies the error signal and generates the
required angle (α) to drive the error to zero, i.e., the load rms
voltage is brought back to the reference voltage. In the PWM
generator, the sinusoidal signal Vcontrol is compared against
a triangular signal (carrier) in order to generate the switching
signals for the VSC valves [11]. The main parameters of the
sinusoidal PWM scheme are the amplitude modulation index
Ma of signal Vcontrol and the frequency modulation index Mf
of the triangular signal. The amplitude index Ma is kept fixed
at 1 pu.
Where Vcontrol is the Peak amplitude of the signal.
Vtri is the peak amplitude of the Triangular signal.
In order to obtain the highest fundamental voltage component
at the controller output, the switching frequency is set at 450
Hz. The frequency of modulation index is given by,
Where M f is the frequency of modulation index.
Fs, is the switching frequency.
Ff is the fundamental frequency.
In this paper, balanced network and operating conditions
are assumed. The modulation angle (δ) is applied to the PWM
generator in phase A. The angle for phases B and C are
shifted by 240° and 120°, respectively.
Fig.4 PI Regulator
IV. D-STATCOM MODELING USING MATLABSIMULINK
Fig. 3 shows the test system used to carry out the various DSTATCOM simulations presented in this section. The test
system composes a 230 kV, 50 Hz generation system,
represented by a Thevenin equivalent, feeding into the
primary side of a 3-winding transformer. A varying load is
connected to the 11 kV, secondary side of the transformer. A
two-level D-STATCOM is connected to the 11 kV tertiary
winding to provide instantaneous voltage support at the load
point.
Fig.3 D-STATCOM Controllers
Proportional Integral (PI) controller: The proportional and
Integral (PI) controllers were developed because of the
desirable property that systems with open loop transfer
functions of type 1 or above have zero steady state error with
respect to a step input it terms is important to increase the
speed of the response and also to eliminate the steady state
error adjusting the process control inputs.
Proportional Action: Responds quickly to changes in error
deviation.
Integral Action: Is slower but removes offsets between the
plant’s output and the reference.
The PI regulator is:
Fig.5 Modeling of D-STATCOM for voltage sag and
voltage swell
1652
David and Cholleti
Implementation of SPWM Technique in DSTATCOM for Voltage Sag and Swell
International Electrical Engineering Journal (IEEJ)
Vol. 5 (2014) No.12, pp. 1649-1654
ISSN 2078-2365
http://www.ieejournal.com/
V. EXPERIMENTAL RESULTS
A. Voltage Sag - Without D-STATCOM
In the first case simulation is did without DSTATCOM and a
three phase-to-ground fault is applied at point A, via a fault
resistance 0.20 Ω, Ground Resistance 0.001. The fault is
created for the duration of 0.3seconds to 0.5seconds.it if
found that there is voltage sag. The output wave for the load
without D-STATCOM shown in below figure.
.
D. Voltage Swell - With DSTATCOM
The second simulation is carried out using the same scenario
as above, but now D-STATCOM is connected to the system,
then the voltage swell is mitigated almost completely, and the
rms voltage at the sensitive load point is maintained at 98%
as shown in below figure.
B. Voltage Sag - With DSTATCOM
The second simulation is carried out using the same scenario
with DSTATCOM, then the voltage sag is mitigated almost
completely .The output wave for the load with D-STATCOM
shown in below figure.
VI. CONCLUSIONS
C. Voltage Swell - Without D-STATCOM
The first simulation contains no D-STATCOM and a
three-phase fault is applied at point A, during the period
300-600ms. The voltage swell at the load point is 20% with
respect to the reference voltage, as shown in below figure.
In this work, the investigation on the role of Distribution
Static Synchronous Compensator (D-STATCOM) can
compensate the voltage sag and swells under faulty
condition. In order to achieve improved power quality levels
simulated with or without DSTATCOM connected to the
distribution system. Compensation techniques of custom
power electronic device D-STATCOM with SPWM was
presented. The control scheme was tested under a wide range
of operating conditions, and it was observed to be very robust
in every case. For modeling and simulation of a
D-STATCOM by using the highly developed graphic
facilities available in MATLAB/SIMULINK were used. The
simulations carried out here showed that the D-STATCOM
provides relatively better voltage regulation capabilities. It
can be concluded that DSTATCOM improves the power
quality and remove the voltage Sag/Swell condition in
distribution network.
1653
David and Cholleti
Implementation of SPWM Technique in DSTATCOM for Voltage Sag and Swell
International Electrical Engineering Journal (IEEJ)
Vol. 5 (2014) No.12, pp. 1649-1654
ISSN 2078-2365
http://www.ieejournal.com/
VII. REFERENCES
[1] Manoj nair “Power quality” text book balaji learning
published Edition: 11 is bn no. 978-81-910618-6-4.
[2] S. Ravi Kumar, S.Sivanagaraju, "Simualgion of
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engineering and applied science, vol. 2, no. 3, pp. 7-13, June
2007
[3] H. Hingorani, "Introducing custom power", IEEE
Spectrum, vol.32, no.6, pp. 41 48, June 1995.
[4] N.G. Hingorani and L. Gyugyi, “Understanding FACTS:
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Systems”, 1st edition, The Institute of Electrical and
Electronics Engineers, 2000.
[5] Dr. S.M. Ali B.K.Prusty M.K.Dash S.P. Mishra. “Role of
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renewable energy system.” Journal of Engineering Research
and Studies E-ISSN0976-7916.
[6]
Hendri Masdi, Norman Mariun Senior MIEEE,
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[6] G. Venkataramana,and BJohnson, "A pulse width
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IEEE Trans. Power Delivary, vol. 12, pp. 844-849, Apr.
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[7] L Xu, O. Anaya-Lara, V.G.Agelidis, and E. Acha,
"Development of prototype custom power devices for power
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[8] W. Freitas, A. Morelato, "Comparitive study between
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[9] Veeraiah Kumbha, N. Sumathi “Power quality
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[10] Pradeep Kumar, Niranjan Kumar & A.K.Akella.
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[11] A. Hernandez, K. E. Chong, G. Gallegos, and E. Acha,
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[12] S. Ravi Kumar, S. Sivanagaraju, "Simualgion of
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engineering and applied science, vol. 2, no. 3, pp. 7-13, June
2007
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Implementation of SPWM Technique in DSTATCOM for Voltage Sag and Swell