Voltage Flicker Analysis and its Mitigation by STATCOM for Power Quality Improvement

6 International Journal for Modern Trends in Science and Technology
Volume: 2 | Issue: 07 | July 2016 | ISSN: 2455-3778IJMTST
Voltage Flicker Analysis and its Mitigation by
STATCOM for Power Quality Improvement
Mekathoti Ravi Kumar1
| Dr. D. Ravi Kishore2
1PG Scholar(HVE),Department of EEE,Godavari Institute of Engineering and Technology, Rajahmundry.
2Professor & Head,Department of EEE,Godavari Institute of Engineering and Technology,Rajahmundry.
Voltage flicker is considered as one of the most severe power quality problems (especially in loads like
electrical arc furnaces) and much attention has been paid to it lately. The reason for this disturbance is
mainly due to the large nonlinear loads such as electric arc furnaces. Due to the latest achievements in the
semiconductors industry and consequently the emergence of the compensators based on voltage source
converters, FACTS devices have been gradually noticed to be used for voltage flicker compensation.
This paper covers the contrasting approaches; dealing with the voltage flicker mitigation in three stages
and assessing the related results in details. Initially, the voltage flicker mitigation, using FCTCR (Fixed
Capacitor Thyristor Controlled Reactor), was simulated. Secondly, the compensation for the Static
Synchronous Compensator (STATCOM) has been performed. The voltage flicker compensation by 8– pulse as
well as 12 – pulse static synchronous compensator (STATCOM) has been performed.
This paper deals with the voltage flicker mitigation and reduction in total harmonic distortion (THD) and
compared the results in detail. The obtained results show that STATCOM is very efficient and effective for the
compensation and mitigation of voltage flicker and harmonics all the simulation results have been performed
on the MATLAB Software.
KEYWORDS: Power Quality, Voltage Flicker, Mitigation, STATCOM
Copyright © 2016 International Journal for Modern Trends in Science and Technology
All rights reserved.
I. INTRODUCTION
Some industry processes such as induction and
arc furnaces, car crushers, mine machinery, and
others present large fluctuating loads to the
supply. These fluctuations cause small variations
on the supply voltage at the point of common
coupling to other users. While the voltage variation
may not be large in magnitude it is sufficient to
cause the output of electrical lights to fluctuate or
flicker. This effect can cause significant annoyance
to other users and must be kept below the
threshold of awareness [1].
The solution lies in the use of high speed IGBT
inverter based shunt connected voltage regulators.
A inverter based active VAR source is effective in
combating flicker because it can modulate the
current flowing in the supply very quickly at
sufficient scale to create a correction voltage on the
supply impedance [2]. The inverter will update the
current flow many times per cycle giving effective
control. It can also manage the available VARs to
optimise the PST (rather than just the % variation)
and to limit the impact on protection systems fault
currents [3-6].
II. OBJECTIVE OF THE PAPER
The causes of power quality problems are
generally complex and difficult to detect.
Technically speaking, the ideal AC line supply by
the utility system should be a pure sine wave of
fundamental frequency (50/60Hz).Different power
quality problems, their characterization methods
and possible causes are discussed above and
which are responsible for the lack of quality power
which affects the customer in many ways. We can
therefore conclude that the lack of quality power
can cause loss of production, damage of equipment
or appliances or can even be detrimental to human
health [7-8]. It is therefore imperative that a high
standard of power quality is maintained. This
project demonstrates that the power electronic
ABSTRACT

Voltage Flicker Analysis and its Mitigation by STATCOM for Power Quality Improvement
based power conditioning using custom power
devices like DSTATCOM can be effectively utilized
to improve the quality of power supplied to the
customers.
The aim of the project is to implement
DSTATCOM with different control strategies in the
MATLAB, simulink using Simpower systems tool
box and to verify and compare the results through
various case studies applying different loads and
study them in detail [9].
The term flicker is sometimes considered
synonymous with voltage fluctuations, voltage
flicker, light flicker, or lamp flicker. The
phenomena being referred to can be defined as a
fluctuation in system voltage that can result in
observable changes (flickering) in light output.
Because voltage flicker is mostly a problem when
the human eye observes it, usually it is considered
to be a problem of perception. There are, however,
rare cases where voltage flicker can affect
equipment operation such as electric drives and
UPS systems. Voltage flicker can be separated into
two types: cyclic and noncyclic. Cyclic flicker is a
result of periodic voltage fluctuations in the system
voltage, with noncyclic referring to occasional
voltage fluctuations. An example of
sinusoidal-cyclic flicker is shown in Figure 1.As
shown in Figure 1, flicker is simply amplitude
modulation where the main signal (60Hz for North
America) is the carrier signal and flicker is the
modulating signal. The usual method for
expressing voltage flicker is similar to that of
amplitude modulation. Voltage flicker is usually
expressed as a percent of the total change in
voltage with respect to the average voltage (ΔV/V)
over a specified time interval [10].
Fig 1 : Example Graph of Voltage Flicker
Fig 2 : General Flicker Curve
A. Sources of Flicker
Typically speaking, voltage flicker occurs on
relatively weak systems with a low short-circuit
ratio. This, in combination with considerable
variations in line current over a short period of
time, results in voltage flicker. As the load
increases, the current in the line increases, thus
increasing the voltage drop across line. This
phenomenon results in a sudden reduction in bus
voltage. Depending upon the change in magnitude
of voltage and frequency of occurrence, this could
result in observable amounts of voltage flicker. If a
lighting load were connected to the system in
relatively close proximity to the fluctuating load,
observers would see this as a dimming (or
flickering) of the lights. A common situation which
could result in voltage flicker would be a large plant
located at the end of a weak distribution feeder.
A common load which often causes voltage
flicker would be an electric arc furnace (EAF) or
welder. EAFs are non-linear, time-varying loads,
which often cause large voltage fluctuations and
harmonic distortion. Large induction machines
undergoing startup or widely varying torque
changes are also known to produce voltage
fluctuations on systems. As shown in Figure 3, as
an induction machine is started up, most of the
power drawn by the motor is reactive. This results
in a large voltage drop across distribution lines.
Figure 4 demonstrates the affect on voltage of
induction motor starting and torque variations.
Although starting large induction machines
across-the-line is not considered to be a
recommended practice, it does however
occasionally occur. Generally, motors are brought
up to speed using reduced voltage starters or
variable speed drives.
B. Interharmonics
In certain circumstances, superimposed
interharmonics in the supply voltage can lead to
oscillating luminous flux and cause light flicker.
Voltage interharmonics are components in the
harmonic spectrum that are non-integer multiples
of the fundamental frequency. This phenomenon
can be observed with incandescent lamps as well
as with fluorescent lamps.
Sources of interharmonics include static
frequency converters, cycloconverters, sub -
synchronous converter cascades, induction
machines and arc furnaces.

Fig 3 : Real and Reactive Power During Induction Machine
Startup
III. INTRODUCTION TO POWER QUALITY
If there is any deviation of voltage, current and
frequency at the load side then it is said to be
power quality problem. Due to these power quality
problems the performance of various sensitive
loads is very poor. If we said that the power quality
is good the voltage should be within permissible
limits. The shape of the wave form should be pure
sinusoidal. In all the three phases voltage should
be same. Power supply should be consistent i.e.
unremitting availability without break.
Contemporary industrial machines and
business-related computer networks are lying face
down to many diverse failure modes. When the
congregation line stops, or the computer network
crashes for no obvious reason, very frequently the
electric power quality is suspected. Power quality
problems may be very difficult to troubleshoot, and
often the electric power may not have any relation
to the actual problem.
Fig 4: Power quality and reliability
Both the reliability and quality of supply are
equally important. For example, a consumer that is
connected to the same bus that supplies a large
motor load may have to face a severe dip in his
supply voltage every time the motor load is
switched on. In some extreme cases even we have
to bear the black outs which is not acceptable to
the consumers. There are also sensitive loads such
as hospitals (life support, operation theatre,
patient database system), processing plants, air
traffic control, financial institutions and numerous
other data processing and service providers that
require clean and uninterrupted power. In
processing plants, a batch of product can be ruined
by voltage dip of very short duration. Such
customers are very wary of such dips since each
dip can cost them a substantial amount of money.
Even short dips are sufficient to cause contactors
on motor drives to drop out. Stoppage in a portion
of process can destroy the conditions for quality
control of product and require restarting of
production. Thus in this scenario in which
consumers increasingly demand the quality power,
the term power quality (PQ) attains increased
significance [13].
Transmission lines are exposed to the forces of
nature. Furthermore, each transmission line has
its load ability limit that is often determined by
either stability constraints or by thermal limits or
by the dielectric limits. Even though the power
quality problem is distribution side problem,
transmission lines are often having an impact on
the quality of the power supplied. It is however to
be noted that while most problems associated with
the transmission systems arise due to the forces of
nature or due to the interconnection of power
systems, individual customers are responsible for
more substantial fraction of the problems of power
distribution systems.
IV. INTRODUCTION TO FACTS DEVICES
Flexible AC Transmission Systems, called
FACTS, which are power electronics devices. These
devices have high controllability in power system.
There are several FACTS devices which are used to
control the power system. For the most part of the
applications the controllability is used to avoid cost
intensive [14]. FACTS-devices provide a better
edition to changing functioning conditions and
improve the usage of active installations. The basic
applications of FACTS devices are:
 Voltage flicker compensation
 To control Power flow,
 Increase of transmission capability,
 To Voltage control,
 To compensate the Reactive power,
 To improve the Stability,
 For improvement of Power quality,
 For Power conditioning,
 Interconnection of renewable and distributed
generation and storages.
According to IEEE FACTS can be defined as AC
Transmission Systems incorporating power
electronic devices other controllers (static
controllers) to improve the Active Power Transfer
Capability and controllability. Due to the increase
in industries day by day there is a chance to

increase in power demand. This leads to increase
power system stabilizers. Due to rapid growth of
power system stabilizers there are some
disadvantages. Power outages and power
interruptions are some of the problems which
affect the customer as well as economy of any
country. The above constraints affect the power
quality. These problems can be overcome by
improving the power system control. FACTS
devices are one of the power system controllers to
compensate the power quality problems. Figure
5 shows a number of basic devices separated into
the conventional ones and the FACTS-devices [15].
Fig 5: Overview of FACTS devices
V. VOLTAGE FLICKER
“Voltage flicker” does not actually exist, though
this term is often heard. When lamps produce
fluctuating light levels, and this is recognized by
someone, we call this, “light flicker,” or simply,
“flicker.” Flicker can be produced either by a
problem in the light source or a fluctuation in the
source voltage. If someone complains of flicker, and
it is caused by voltage fluctuation, then its cause
needs to be found. Sometimes flicker is caused by
load fluctuations in the customer’s equipment near
the flickering lamp. Such problems can often be
easily solved. If not, investigation must be taken
beyond the meter into the utility system. This
usually dictates that the flicker must be objectively
measured. 4.1.1 Flicker Meter Flicker produced by
fluctuating source voltage is measured indirectly
by a flicker meter. The modern flicker meter
measures voltage fluctuation and infers light
flicker by taking into account the following: how
often the voltage fluctuation occurs, how abruptly
the voltage fluctuates, the kind of lamp, the
sensitivity of the eye to light, and the brain’s
perception. All of these factors are modeled in a
modern IEEE 1453 compliant flicker meter (this
measurement is more complex than simply
measuring voltage fluctuation and frequency).
Fig 6: Voltage Flicker output voltage waveform
Fortunately, despite its internal complexity, an
IEEE flicker meter’s output is simple: if the output
is greater than 1.0, the flicker is generally irritable
to humans; if less than 1.0, it is not. These results
have been successfully validated with many years
of real-world testing in several countries. The
flicker meter’s main output is in a unit called Pst,
meaning, “Perception of light flicker in the short
term.” Planned load characteristics should be
obtained directly from the customer or equipment
manufacturer. Gathering data for existing
fluctuations requires the use of a recording
voltmeter having a time resolution smaller than the
occurrence of the flicker. Many recording
voltmeters do not have sufficient resolution to
perform this task.
VI. VOLTAGE FLICKER COMPENSATION
Voltage oscillation was produced by a
3-phase flicker source. The Studied power system
with complete STATCOM control and flicker source
scheme is shown in figure 1. A STATCOM is used to
regulate voltage on a 69KV transmission Network.
A 440V load connected to a bus B1 through a
69KV/440V transformer represents a plant
absorbing continuously charging currents similar
to an arc furnace, thus producing voltage flicker.
The STATCOM regulates the bus B3 voltage
through the leakage reactance of the 3-phase two
winding transformers by generating a secondary
voltage .
Fig.7 Voltage Flicker Compensation current wave form

A. Controlling System
The concept of instantaneous reactive power is
used for the controlling system. Following this, the
3-phase voltage upon the use of the park presented
by Akagi has been transformed to the synchronous
reference frame (Park or dq0 transformation). This
transformation leads to the appearances of three
instantaneous space vectors: Vd on the d-axis (real
or direct axis), Vq t h e q-axis (imaginary or
quadrature axis) and V0, from the 3-phase voltage
of Va, Vb and Vc. The related equations of this
transformation, expressed in the MATLAB
software, are as follows:
A new technique based on a novel control
algorithm, which extracts the voltage disturbance
to suppress the voltage flicker, is presented in this
thesis. The concept of instantaneous reactive
power is used for the controlling system. Following
this 3Ø flicker voltage has been transformed to
synchronous reference frame by the use of abc to
dqo transformation (Park’s transformation). To
implement the synchronous reference frame some
kind of synchronizing system (phased looked loop)
should be used. 3Ø AC system load voltage is the
input to the phase locked loop (PLL), this PLL can
be used to synchronize on a set of variable
frequency, and 3Ø sinusoidal signals.3Ø PLL block
provides three outputs.
Fig.8 Block diagram of the investigated power system
The word “data” is plural, not singular. The
subscript for the permeability of vacuum µ0 is zero,
not a lowercase letter “o.” The term for residual
magnetization is “remanence”; the adjective is
“remanent”; do not write “remnance” or “remnant.”
Use the word “micrometer” instead of “micron.” A
graph within a graph is an “inset,” not an “insert.”
The word “alternatively” is preferred to the word
“alternately” (unless you really mean something
that alternates). Use the word “whereas” instead of
“while” (unless you are referring to simultaneous
events). Do not use the word “essentially” to mean
VII. SIMULATION RESULTS
Fig .9 .Simulink diagram of 12-pulse voltage source
converter STATCOM
Fig.10 Control circuit for 12-pulse voltage source converter
STATCOM
Fig.11. Output Voltage and Current of FCTCR
A. Compensation by Four Leg Inverter
The three-phase 8 – pulse VSC based
STATCOM is shown in figure15 and figure16 .
There are switches in the converter each converter
is made up of Thyristor/ MOSFET with a diode
connected in anti-parallel. In this type of
STATCOM, each witch is triggered and turn off one
time per line voltage cycle. In this case, each switch
in a single branch is conducted during a half-cycle
(180 degree) of the fundamental period. The
combined pulses of each leg have a 120 degrees
phasedifference to produce a balanced set of
Discrete,
Ts = 1e-005 s.
powergui
A
B
C
Three-Phase Source
A
B
C
a
b
c
Three-Phase
V-I Measurement3
Vabc
IabcA
B
C
a
b
c
Three-Phase
V-I Measurement2
Vabc
Iabc
A
B
C
a
b
c
Three-Phase
V-I Measurement1
A
B
C
a
b
c
Three-Phase
V-I Measurement
A
B
C
a
b
c
Three-Phase
Transformer
(Two Windings)1
A
B
C
a
b
c
Three-Phase
Transformer
(Two Windings)
A
B
C
A
B
C
Three-Phase
Series RLC Branch
N
A
B
C
Three-Phase
Programmable
Voltage Source
A
B
C
Three-Phase
Parallel RLC Load
A
B
C
A
B
C
Three-Phase
PI Section Line
Out1
Out2
Out3
Subsystem1
Conn1
Conn2
Conn3
Subsystem
Scope4
Scope3
Scope1
Scope
-T-
Goto
Vabcfl
From15
3
Out3
2
Out2
1
Out1
abc
sin_cos
dq0
abc_to_dq0
Transformation
Step
[s23]
Goto9
[s22]
Goto8
[s21]
Goto7
[s16]
Goto6
[s15]
Goto5
[s14]
Goto4
[s13]
Goto3
[s12]
Goto2
[s26]
Goto12
[s25]
Goto11
[s24]
Goto10
[s11]
Goto1
-K-
Gain
Vabcfl
From8
[Vabcload]
From7
Vabcfl
From6
alpha_deg
A
B
C
Freq
Block
PY
PD
Discrete Synchronized
12-Pulse Generator
PI
Discrete
PI Controller
Vabc(pu)
Freq
wt
Sin_Cos
Discrete
3-phase PLL
0
Constant
Add
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
-1.5
-1
-0.5
0
0.5
1
1.5
Time(mecs)
VolatgeInP.U
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
-1.5
-1
-0.5
0
0.5
1
1.5
Time(msecs)
CurrentinP.U

voltages. By controlling the triggering angle of the
thyristor we can control the generated voltage of
the STATCOM and also the absorbed/injected
power of the STATCOM.
Fig 12.Output Voltage and Current of Four Leg Inverter
Fig.13 Output Voltage and Current of Four Leg Inverter in
THD
B. Compensation 12 Pulse VSC-STATCOM
Fig.14 Output Voltage and Current of 12-Pluse Inverter
Fig 16. Output Voltage and Current of 12-Pluse Inverter in
THD
VIII. CONCLUSION
In this paper, the application of three phase
inverter technology based on voltage-source
converters for voltage flicker mitigation has been
investigated and simulation results emphasized its
significant effect. A 6 – pulse STATCOM is
decreasing the voltage flicker by 50 %. However,
there is injection of the harmonic from 6-pulse
inverter into the system which can be improved
with the increase of the voltage source converters of
STATCOM using a 12-pulse STATCOM equipped
with a harmonic filter. The obtained results clearly
demonstrate that 12-pulse STATCOM equipped
with a harmonic filter can reduce the voltage flicker
completely and the output is obtained with
minimum THD value
REFERENCES
[1] J. Sun, D. Czarkowski, Z. Zabar, “Voltage Flicker
Mitigation Using PWM-Based Distribution
STATCOM”, IEEE Power Engineering Society
Summer Meeting, Vol.1, (21-25 July 2002), pp.
616-621.
[2] N. G. Hingorani, L.Gyugyi, "Understanding FACTS",
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[3] Rozmyslaw , Miensik, Ryszard.pawelk , “Application
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0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-1
-0.5
0
0.5
1
Time(msecs)
VoltageInPu
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-1
-0.5
0
0.5
1
Time(msecs)
CurrentinP.U
0 0.1 0.2 0.3 0.4 0.5
-1
0
1
Selected signal: 30 cycles. FFT window (in red): 1 cycles
Time (s)
0 200 400 600 800 1000
0
1
2
3
4
Frequency (Hz)
Fundamental (60Hz) = 1.144 , THD= 2.77%
Mag(%ofFundamental)
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
-1
-0.5
0
0.5
1
Time(msecs)
VolatgeinP.U
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
-1
-0.5
0
0.5
1
Time(msecs)
CurrentinP.U
0 0.05 0.1 0.15 0.2 0.25 0.3
-0.5
0
0.5
Selected signal: 18 cycles. FFT window (in red): 1 cycles
Time (s)
0 200 400 600 800 1000
0
0.005
0.01
0.015
Frequency (Hz)
Fundamental (60Hz) = 0.9999 , THD= 0.51%
Mag(%ofFundamental)

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