International Journal of Engineering Trends and Technology (IJETT) – Volume22 Number3- April2015
Efficient Power Stability using Parallel Structure
SV-PWM Based DSTATCOM
1
Sangeeta Singh1, Asst. Prof Pushpendra Gautam2
M Tech Research Scholar, 2Research Guide, Department of Electrical Engineering
Maxim Institute of Technology, Bhopal
Abstract - The stability of power in any industry is a basic need to
make machines live longer and have utmost output from them.
There are various technique has been given to make power
machines efficient to operate. In this research work a distributed
static compensator (DSTATCOM) is proposed for the stability
compensation in power systems. The proposed model of
DTATCOM utilizes the space vector pulse width modulation (SVPWM) in parallel so that the compensation effectively stables the
power of the machines. From the results it is clear that the
proposed model gives optimum performance for stability.
Keywords-DTATCOM, SV-PWM, Stability and Parallel Structure.
I.
INTRODUCTION
Recently, Flexible Alternative Current Transmission System
(FACTS) controllers have been proposed to enhance the
transient or dynamic stability of power systems. All through
the preceding decade, a number of control devices under the
term FACTS technology have been proposed and
implemented. Amongst all FACTS devices, static
synchronous compensators (STATCOM) plays much more
important role in reactive power compensation and voltage
support because of its attractive steady state performance and
operating characteristics. The basic principle of a STATCOM
installed in a power system is the generation ac voltage
source by a voltage source inverter (VSI) connected to a dc
capacitor. Active and reactive power transfer among the
power system and the STATCOM is caused by the voltage
difference across this reactance.
The basic function of the STATCOM is for the line voltage
control that is implemented by an ac voltage controller in the
STATCOM by regulating the reactive power exchange
between the STATCOM and power system. A second
controller installed in the STATCOM is the dc voltage
controller that regulates the dc voltage across the dc capacitor
of the STATCOM. In conventional control schemes, both the
voltage regulators are proportional integral (PI) type
cascaded controllers. Recently, a linear multivariable
controller approach has been used for the STATCOM
controller design for better performance. However, since the
complete model of STATCOM is highly nonlinear, the linear
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approach obviously dose not lead to better dynamic
decoupling.
Need for Dynamic voltage compensation:
High Intensity Discharge (HID) lamps used for industrial
illumination get extinguished at voltage dips of 20%. Also,
critical industrial equipment like Programmable Logic
Controllers (PLCs) and Adjustable Speed Drives (ASDs) are
adversely affected by voltage dips about 10%. The initial
current of the induction motor being 6 times its rated current
it provides the sag mitigation. Voltage sag has been defined
as a reduction in the voltage magnitude from its nominal
value for a duration ranging from a few milli seconds to one
minute.
Solution for Dynamic Voltage compensation:
Solution approaches to the voltage disturbance problem, by
active devices, may involve either i) a series injection of
voltage, and ii) the shunt injection of reactive current. The
Static Var Compensator (SVC) and the STATCOM are the
available shunt compensation devices.
The speed of devices for power quality improvement
(FACTS), which was made possible by the evolution of
power electronics components, allows for the solving of
problems such as voltage stability, transient improvement,
oscillations damping and improvement of the lines
performance. The term FACTS describes a wide range of
controllers, many of which incorporate large power
electronic converters, which may increase the flexibility of
power systems making them more controllable. Some are
already well established while some are still in the research
or development stage.
II.
STATCOM TECHNOLOGY
STATCOM systems essentially consist of a DC voltage
source behind self commutated inverters using insulated gate
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International Journal of Engineering Trends and Technology (IJETT) – Volume22 Number3- April2015
bipolar transistor (IGBT), gate turn-off (GTO) thyristors and
an interconnecting transformer.
reverse, if V2 is higher than V1, Q is flowing from V2 to V1
(STATCOM is generating reactive power). Whereas the
amount of reactive power is given by
A capacitor connected on the DC side of the VSC acts as a
DC voltage source. In the steady state voltage V2 has to be
phase shifted slightly behind V1 in order to compensate for
transformer and VSC losses and to keep the capacitor
charged. Two VSC technologies could be used for the VSC.
The STATCOM differs from other reactive power generating
devices (such as Capacitors, Static Var Compensators etc.) in
the sense that the ability for energy storage is not a rigid
necessity but is only required for system unbalance or
harmonic absorption. As a consequence, the not-a-so-strict
requirement for large energy storage device makes
STATCOM more robust and it also enhances the response
speed.
Basically, there are two control objectives implemented in
the STATCOM. One is ac voltage regulation of power
system at the bus where the STATCOM is connected and the
other is dc voltage control across the capacitor inside the
STATCOM.
III.
Fig. 2.1 Basic STATCOM Configuration
The voltage source inverter set connects to the power system
via a multi-winding or two winding inverter transformer,
depending upon the application. The figure shows the basic
STATCOM configuration. Inverter and DC voltage source
could be modeled as a variable voltage source. The power
system also can be modeled as a voltage source. Inductor
representing the leakage reactance of the transformer
connects the two voltage sources.
The principle of operation of the STATCOM is explained on
the figure above showing the active and reactive power
transfer between a source V1 and a source V2. In the figure,
V1 signifies the system voltage to be controlled and V2 is the
voltage generated by the VSC.
In steady state operation, the voltage V2 generated by the
VSC is in phase with V1 (δ=0), so that only reactive power is
flowing (P=0). If V2 is lower than V1, Q is flowing from V1
to V2 (STATCOM is absorbing reactive power). Under the
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PROPOSED MODEL
The model to achieve optimum stability proposed in this
paper is displayed in the given diagram. The model has key
components are parallel DSTATCOM, power supply,
universal bridge, IGBT, Discrete SV-PWM, Discrete PI
Controller, 2nd order Filter, Memory and 3-phase PLL etc.
The parallel structure of DSTATCOM is the basic idea of
making the stability in the power systems. Stability is the
tendency of the power system to revert back to its original
undisturbed state once the perturbations or disturbances are
over. This disturbance may be caused due to a fault, or the
loss of a generator, or a fault in the line. The operating point
of the system can change after the adjustment of the system
to a new operating point post fault. This is known as the
transient period and the behavior of the system during this
period is crucial in defining the stability of the system.
Pulse Width Modulation variable speed drives are
increasingly applied in many new industrial applications that
require superior performance. The most widely used PWM
schemes for three-phase voltage source inverters are carrierbased sinusoidal PWM and space vector PWM (SVPWM).
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International Journal of Engineering Trends and Technology (IJETT) – Volume22 Number3- April2015
There is a rising trend of using space vector PWM (SVPWM)
because of their easier digital realization and better dc bus
utilization.
The proposed model is shown in the given Fig. 3.1.
Fig. 3.1 Model of the Proposed Methodology
IV.
SIMULATION RESULTS
The proposed model for stability in systems is explained in
the previous section of the paper. The simulation waveforms
are explained in this section.
In the above figure the waveforms of the three phase voltage,
current, load current and controlled current waveforms are
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shown. As it has shown the voltage waveform has distortions
on a regular interval and the effect of these distortions are
increasing with respect to time. Whereas the load current
waveforms are also visible in the figure which has major
unwanted variations in the load current and that will cause to
severe system instability. Now there is a need to compensate
these distortions in the power system to achieve maximum
stability in the system.
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Fig. 4.1 Waveforms of three phase voltage Vabc , three phase current Iabc , Load Current and Controlled Current
Fig. 4.2 Waveforms of the DC voltage, load current, phase shifts and active and reactive power where instability of the system
is visible in DC voltage and load current waveforms.
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International Journal of Engineering Trends and Technology (IJETT) – Volume22 Number3- April2015
Other system waveforms are shown in the Fig. 4.2, where DC
voltage waveforms, distorted load current waveform, phase
shift and active/reactive power plots are main responses of
the system. In the Fig. 4.3 the waveforms of the controlled
voltages V1 and V2 are shown with PWM voltage and stable
output voltage.
Fig. 4.3 Waveforms of the controlled voltages, PWM voltage and output voltages
V.
CONCLUSION AND FUTURE SCOPE
The proposed model is simulated on simulation tool and the
results are shown in the previous section of the paper. From
the simulation results is can be say that the parallel structure
of the DSTATCOM with the SV-PWM is significant
technique to achieve stability in the power system. The stable
output waveforms say everything about the proposed model.
This structure of DSTATCOM will helpful in the other
domains of power systems to reap the complete performance
of the machines within its lifetime.
Other techniques will help to achieve more stable system
integration with the existing proposed model e.g. fuzzy logic
will help to reduce instability up to certain extent.
[3] A.Ghosh and G. Ledwich, Power Quality Enhancement
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reactive power compensators comprising switching
devices without energy storage components, IEEE Trans.
Ind. Appl., vol. IA-20, no. 3, pp. 625-630, May 1984.
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Author’s Profile
Sangeeta Singh is a research scholar at Maxim Institute of
Technology,
under
Rajiv
Gandhi
Proudyogiki
Vishwavidyalaya, Bhopal. She is pursuing her Master of
Technology in Power System. Her research interest is control
strategies of distribution static compensator.
[12] Ch. Siva Koti Reddy, Dr. P. Linga Reddy “A
DSTATCOM-Control Scheme for Power Quality
Improvement of Grid Connected Wind Energy System
for Balanced and Unbalanced Non linear Loads”
International Journal of Modern Engineering Research
(IJMER) Vol.2, Issue.3, May-June 2012 pp-661-666
ISSN: 2249-6645
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