International Journal of Scientific & Engineering Research, Volume 5, Issue 2, February-2014
ISSN 2229-5518
94
Power quality improvement using Multitype FACTS device.
Pawar Parmanand Ashok, Modak Prakash V.
Abstract— Modern power systems are prone to widespread failures. With the increase in power demand, operation
and planning of large interconnected power system are becoming more and more complex, so power system will
become less secure. Operating environment, conventional planning and operating methods can leave power system
exposed to instabilities. Voltage instability is one of the phenomena which have result in a major blackout. To maintain
security of such systems, it is desirable to plan suitable measures to improve power system security and increase
voltage stability margins. FACTS devices can regulate the active and reactive power control as well as adaptive to
voltage-magnitude control simultaneously because of their flexibility and fast control characteristics. Placement of
these devices in suitable location can lead to control in line flow and maintain bus voltages in desired level and so
improve voltage stability margins.
Index Terms—Injection Transformer, Static var Compensator, Thyristor controlled series capacitor, Voltage source
Transformer, Pulse Width Modulation.
——————————  ——————————
1
I
INTRODUCTION
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n electrical power system, for higher exchange
of
electrical
energy
through
existing
transmission lines, grid companies are very
much interested in raising and controlling the
power flow through the main transmission lines
without losing system reliability.
In the present pace of power system restructuring,
transmission systems are being required to provide
increased power transfer capability and to
accommodate a much wider range of possible
generation patterns. Environmental, right-of-way,
and cost problems are major hurdles for power
transmission network expansion.
Hence, there is an interest in better utilization of
available power system capacities by installing
new devices such as flexible ac transmission
systems (FACTS).
FACTS essentially introduce new degrees of
freedom into the operation of power systems. This
extra flexibility permits the independent
adjustment of certain system variables (such as
power flows) which are normally not controllable.
FACTS devices can be differentiated by their
controllable parameters and by the manner in
which they are realized electronically.
Thus, devices exist which so control of power can
flow in order to have more efficient, reliable
system is in the interest of the transmission system
operator (TSO).
SVC:
A shunt connected static var generator or absorber
whose output is adjusted to exchange capacitive or
Inductive current so as to maintain or control
specific parameters of the electrical power system
(typically bus voltages).
(Fig.1 schematic diagram of svc)
TCSC:
A capacitive reactance compensator which, consist
of a series capacitor bank shunted by a thyristorcontrolled reactor in order to provide a smoothly
variable series capacitive reactance.
(Fig.2 schematic diagram of TCSC)
2
IMPLEMENTATION
2.1 POWER QUALITY
The IEEE Standard Dictionary of Electrical and
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International Journal of Scientific & Engineering Research, Volume 5, Issue 2, February-2014
ISSN 2229-5518
Electronics defines power quality as “the concept
of powering and grounding sensitive electronic
equipment in a manner that is suitable to the
operation of that equipment.” Power quality may
also be defined as “the measure, analysis, and
improvement of bus voltage, usually a load bus
voltage, to maintain that voltage to be a sinusoid at
rated voltage and frequency.”Another definition of
power quality reported in the literature [1] is as
follows:
Power quality is “the provision of voltages and
system design so that the user of electric power can
utilize electric energy from the distribution system
successfully without interference or interruption.”
A broad definition of power quality borders on
system reliability, dielectric selection on equipment
and conductors, long-term outages, voltage
unbalance in three-phase systems, power
electronics and their interface with the electric
power supply and many other areas.
minute is often unending and requires human
intervention to restore the supply. The term
“outage” is also used for long interruption.
However it does not bring out the true impact of
the power interruption. Even an interruption of
half a cycle can be disastrous for a customer with a
sensitive load.
3
METHODOLOGY
3.1 Multi-Type FACTS SYSTEM
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
Multi-Type
FLEXIBLE
ALTERNATING CURRENT TRANSMISSION
SYSTEM which is the most efficient and effective
modern custom power device used in power
distribution networks. Multi-type FACTS 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,
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2.2 Problems Associated With Power Quality
2.2.1 Transients
Transients are unwanted decay with time and
hence not a steady state problem. A broad
definition is that a transient is “that part of the
change in a variable that disappears during
transition from one steady state operating situation
to the other". Another synonymous term which can
be used is surge. Transients are further classified
into two categories (a) Impulsive (b) Oscillatory
2.2.2 Long Duration Voltage Variations
When rms (root mean square) deviations at power
frequency last longer than one minute, then we say
they are long duration voltage variations. They can
be either over voltages which is greater than 1.1p.u
or under voltages which is less than 0.9p.u. Over
voltage is due to switching off a load or energizing
a capacitor bank. Also incorrect tap settings on
transformers can result in over voltages. Under
voltage are the results of actions which are the
reverse of events that cause over voltages i.e.
switching in a load or switching off a capacitor
bank.
2.2.3 Sustained Interruptions
If the supply voltage becomes zero for a period of
time which is greater than one minute, then we can
say that it is a sustained interruption. Normally,
voltage interruption lasting for more than one
95
3.2 Principle Operation of Multi-Type Facts
Device
A Multi-type FACTS is a solid state power
electronics switching device consisting of either
GTO or IGBT, a capacitor bank as an energy
storage device and injection transformers. It is
linked in series between a distribution system and
a load that shown in Figure 2.1. The basic idea of
the Multi-type FACTS is to inject a controlled
voltage generated by a forced commuted converter
in a series to the bus voltage by means of an
injecting transformer. A DC to AC inverter
regulates this voltage by sinusoidal PWM
technique. All through normal operating condition,
the Multi-type FACTS injects only a small voltage
to compensate for the voltage drop of the injection
transformer and device losses. However, when
voltage sag occurs in the distribution system, the
Multi-type FACTS control system calculates and
synthesizes the voltage required to preserve output
voltage to the load by injecting a controlled voltage
with a certain magnitude and phase angle into the
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International Journal of Scientific & Engineering Research, Volume 5, Issue 2, February-2014
ISSN 2229-5518
distribution system to the critical load [18]
(Fig.3.schematic diagram of Multi- type FACTS)
3.3 Basic Arrangement of Multi-Type Facts
Device
The Multi-type FACTS device mainly consists of
the following components:
3.3.1INJECTION TRANSFORMER
Three phase two transformers are connected in
series with each of the distribution feeder to couple
the VSC (at the lower voltage level) to the higher
distribution voltage level. It links the Multi-type
FACTS system to the distribution network via the
HV-windings and transforms and couples the
injected compensating voltages generated by the
voltage source converters to the incoming supply
voltage. In addition, the Injection transformer also
serves the purpose of isolating the load from the
Multi-type FACTS system (VSC and control
mechanism).
3.3.2 DC CHARGING UNIT
The dc charging circuit is used after sag
compensation event the energy source is charged
again through dc charging unit. It is also used to
maintain dc link voltage at the nominal dc link
voltage.
3.3.3 VOLTAGE SOURCE CONVERTER
A VSC is a power electronic system consists of a
storage device and switching devices, which can
generate a sinusoidal voltage at any required
frequency, magnitude, and phase angle. It could be
a 3 phase - 3 wires VSC or 3 phases - 4 wires VSC.
Either a conventional two level converter or a three
level converter is used. There are four main types
of switching devices: Metal Oxide Semiconductor
Field Effect Transistors (MOSFET), Gate Turn-Off
thyristors (GTO), Insulated Gate Bipolar
Transistors
(IGBT),
and
Integrated
Gate
Commutated thyristors (IGCT). Each type has its
own benefits and drawbacks. The IGCT is a recent
compact device with enhanced performance
96
consistencies that allows building VSC with very
large power ratings. GTO is the unidirectional
current device. It can withstand bipolar voltages. It
requires gate pulse signal for turning it ON and
once it get ON, gate pulse is removed. The function
of storage devices is to supply the required energy
to the VSC via a dc link for the generation of
injected voltages. The different kinds of energy
storage devices are Superconductive magnetic
energy storage (SMES), batteries and capacitance.
Two types of VSC they are of following
Series VSC:
It converts the three phase ac supply into dc
supply with the elimination of harmonics by using
the zig-zag transformer. It is connected to the
injection transformer of the circuit. The converted
dc voltage then gets stored by capacitor connected
across the three VSC.
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Shunt VSC:
It converts the dc supply into three phase ac
supply. Shunt VSC is also called as the Static
Synchronous Compensator (STATCOM).
3.3.4 HARMONIC FILTER
As DVR consist of power electronic devices, the
possibility of generation self harmonics is there so
harmonic filter is also become a part of. Multi-type
FACTS the main task of harmonic filter is to keep
the harmonic voltage content generated by the
VSC to the acceptable level. Harmonic filter here
used is the Zig-Zag transformer. The Zigzag PhaseShifting Transformer block implements a threephase transformer with a primary winding
connected in a zigzag configuration and a
configurable secondary winding. The model uses
three single-phase, three- winding transformers.
The primary winding connects the windings 1 and
2 of the single-phase transformers in a zigzag
configuration. The secondary winding uses the
windings 3 of the single phase transformers, and
they can be connected in one of the following
ways:
- Y, Y with accessible neutral, Grounded Y
-Delta (D1), delta lagging Y by 30 degrees
3.3.5. CONTROL AND PROTECTION
A controller is also used for the proper operation of
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International Journal of Scientific & Engineering Research, Volume 5, Issue 2, February-2014
ISSN 2229-5518
the Multi-type FACTS system. Load voltage is
sensed and passed through a sequence analyzer.
The magnitude of load voltage is compared with
reference voltage. Pulse width modulated (PWM)
control technique is applied for inverter switching
so as to generate a three phase 50 Hz sinusoidal
voltage at the load terminals.
4
BASIC SIMULATION DIAGRAM OF POWER
QUALITY IMPROVEMENT USING MULTITYPE FACTS
5
97
CONCLUSION
The present topology illustrates the operation and
control of Multi-type FACTS The system is
extended by adding a series VSC in an adjacent
feeder. The device is connected between two or
more feeders coming from different substation.
The performance of the Multi-type FACTS has
been evaluated under various disturbance
conditions such as voltage sag/swell in either
feeder, fault and load change in one of the feeders.
In case of voltage sag, the phase angle of the bus
voltage in which the shunt VSC is connected plays
an important role as it gives the measure of the real
power required by the load. The Multi-type FACTS
can mitigate voltage sag in Feeder for long
duration between two adjacent feeders which are
not connected.
REFERENCES
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(Fig.4 Simulink model of distribution system with
Multi-type FACTS)
ADVANTAGES :
1) To regulate the load voltage against sag/swell
and disturbances in the system to protect the
nonlinear/sensitive load.
2) The transient stability limit is improved thereby
improving dynamic security of the system and
reducing the incidence of blackouts caused by
cascading outages.
3) They contribute to best possible system
operation by improving voltage profile and
reducing power losses.
4) The steady state or small signal stability region
can be increased by providing auxiliary stabilizing
controllers to damp low frequency oscillations.
5) FACTS controllers such as TCSC can counter the
problem of Sub synchronous Resonance (SSR) .
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[1] Hamid Reza Mohammadi, Ali Yazdian
Varjani,
and
Hossein
Mokhtari,“Multiconverter Unified PowerQuality Conditioning System: Mc- Upqc”
Ieee Ransactions On Power Delivery, Vol.
24,No. 3, July 2009.
[2] R.Rezaeipour and A.Kazemi, “Review of
Novel control strategies for UPQC”
Internal Journal of Electric and power
Engineering 2(4) 241-247, 2008.
[3] S.
Ravi
Kumar
and
S.Siva
Nagaraju“Simulation of DSTATCOM and
[4] DVR in power systems” Vol. 2, No. 3,June
2007 ISSN 1819-6608 ARPN Journal of
Engineering and Applied Sciences.
[5] M.V.Kasuni Perera” Control of a Dynamic
Voltage Restorer to compensate single
phase voltage sags” Master of Science
Thesis, Stockholm, Sweden 2007.
[6] M. Basu, S. P. Das, and G. K. Dubey,
“Comparative evaluation of two models of
UPQC for suitable interface to enhance
power quality,” Elect.Power Syst. Res.,
2007.
[7] A. K. Jindal, A. Ghosh, and A. Joshi,
“Interline
unified
power
quality
conditioner,” IEEE Trans. Power Del, vol.
pp. 364–372, Jan. 2007.