Research Paper

1. International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 6, Issue 3, March 2016)
85
Power Quality Enhancement in Power Distribution System by
Using Fuzzy Logic Controlled D-STATCOM
Jitendra Kumarˡ, Dr. S. K. Srivastava²
1
PG Scholar, 2
Associate Professor, Department of Electrical Engineering, MMMUT Gorakhpur, India 273010
Abstract-This Paper distinguished the problems related
to distribution system in terms of clean power and their
solutions, in the particular of compensation of reactive
power. The abnormalities has been modelled and then
analyzed. The deviations in the distributions system
analyzed by the using D-STATCOM in the real time with
the LCL passive filter. Fuzzy logic control scheme is
implemented for the control of D-STATCOM so that it can
make reactive power and THD under control. A
SIMULINK model has been developed for the proposed
system. Simulink results for various operating conditions
has been obtained and analyzed for the merit of proposed
control technique.
Keywords- D-STATCOM, Voltage Sag, FLC, LCL
passive filter, THD
I. INTRODUCTION
In the present scenario power quality become major
concern with the solid state devices, the performance is
very close to the quality of power which is utilized by the
utility centre. Utilities have the greater interest to utilize
the existing power capacities .Power quality issues
manifested to a undesired current or frequency or voltage
that leads to the system in failure conditions or makes a
misoperation at the consumer end. In today’s
industrializations and modernisations of the power sector
contains solid state power electronics devices like as
IGBTs, MOSFETs and PLCs .All these devices is most
affected by the quality of power such as harmonics,
voltage swells/sag. Major power quality problems is
voltage sags that contributes more than eighty percent of
all these power quality issues. Voltage sags is decrease in
rms amplitude value at the power frequency for a time
period of few seconds. Different fault in the power
system creates a voltage sag in the utility system. Fault at
the customers end increases large current in the load
system, resulted in the starting of motor or enerzitation of
transformer. Typically faults like as single phase to
ground or multiple phase with ground leads a very high
current causes a voltage dip over the system impedance
network. Voltage are hazards for the electronics
equipment used by industry like as adjustable speed
drive, robotics, programmable logic controllers. Different
technique have been applied for the reduction or
mitigations of voltage sag. Some conventional process
are using bank of capacitor, implementation of parallel
connected feeders or apply uninterruptible power
supplies.
The power quality are not completely mitigated due to
high cost of new feeders and controlled compensation of
reactive power. A D-STATCOM (distributed static shunt
compensator) are used for the mitigation of voltage sag
as well as voltage stability, voltage flicker reduction.
This paper consists a D-STATCOM with passive LCL
filter and connected to 11kv distribution system in
parallel or in shunted. The D-STATCOM also improve
the power quality like as low power factor and harmonic
distortion. In this paper section I represent introduction of
test system. Section II describes the power quality issues
such as voltage sag/swells. Section III represents
modelling and principle of operation for the test system.
Fuzzy logic control technique, system implementation
and simulation results are discussed in the section IV,V
and VI respectively.
II. VOLTAGE SAG AND SWELL
Voltage sag and swell is mainly caused by the faulty
conditions short circuit, over load situations and on/off of
high capacity motors. Injections of voltage by DVR to
maintain and restore sensitive voltage to it’s normal
operating value, for achieving zero power or minimum
for compensation to the system by selecting an proper
amplitude and angle between phase for a period of half of
cycle to one minute . Voltage sag can happened at any
instant with 10% to 90% of amplitude ranges of voltage.
Voltage swells are defined as opposite of voltage sag i.e
increment of rms value of voltage or current at frequency
of power for a duration of 0.5 cycle to 60 seconds.
Magnitude of voltage swells ranges from 1.1 to 1.8
increment value.IEE519-1992 and IEEE1159-1995
standard are shown in fig 1
Fig-1 IEEE 159-1995 STANDARD For Voltage Sag

2. International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 6, Issue 3, March 2016)
86
Voltage swells are rarely happen phenomenon in
distribution system i.e not much important as voltage
sag/dip.
III. BASIC STRUCTURE AND OPERATING PRINCIPAL
OF D-STATCOM
The D-STATCOM is voltage source converter based
shunt FACTs devices. It have capacity of absorbing or
generating reactive power. The reactive source could be
controlled. D-STATCOM is connected to the distribution
system by coupling transformer to isolate the D-
STATCOM from the distribution system. It’s need the
device to be implemented as close to the most affecting
loads to enhance the compensation in the distribution
system. D-STATCOM injects only reactive power and
plays major role on the weak ac system. D-STATCOM is
composed of voltage source converter, filter and energy
storage devices as shown in fig 2.
A)Coupling Transformer- It’s used to connect the D-
STATCOM to the distribution system. It’s act as a
isolation between D-STATCOM circuit and
distribution system.
Fig 2- Basic Structure of D-STATCOM
B)VSC(Voltage source Converter)- A voltage
converter are composed of switching devices and
storage devices, producing a sinusoidal voltage at
desired instant of frequency, amplitude and angle of
phase. Application of D-STATCOM is injects the
compensating current into the distribution system
on the basis of unbalance or distortion amount.
Generally IGBTs is choosen as a switching devices.
I out = IL-Is = IL-[(V th- VL)/Z th]
C)DC Link Capacitor- The capacitor act as a storage
devices and provide dc link voltage at the standard
value
D)LCL Passive Filter- The configuration of LCL filter
is shown in fig 3.
Fig 3- LCL Passive Filter
Generally high order LCL filter has been used instead
of conventional L-filter for improving the current
waveform getting from VSI [13]. By using LCL filter
obtaining best attenuation as well as cost saving and size
and weight reduction. To model this following equations
are used.
√
⁄
For efficient LCL passive filter
E) Principal of Operation-
The D-STATCOM are placed for the compensation of
reactive power from which they are interconnected. It is
producing 3 phase alternating voltage to a direct source
of voltage. The magnitude of the voltage are controlled
to maintain amount of reactive power to enhance the
system voltage profile. Generally D-STATCOM voltage
(Vsh) injected with phase the bus voltage (Vt). There is
need of injected energy but reactive power to be absorb
or injected by the D-STATCOM system. The
compensation of reactive power is takes place by the
changing the magnitude of out voltage of D-STATCOM.
The basic operating principal of D-STATCOM is
described by fig 4. The output voltage of IGBTs (Vsh) is
maintained in phase to the bus voltage (Vt) and. current
output changes as Vsh [8,9]
If-
I) Vt < Vsh- Ish leads t by 0 . As a consequence
leading reactive power produced by the D-
STATCOM (i.e Capacitive mode)
II) Vt > Vsh- Ish lag t by 0 . As a consequence
lagging reactive power absorb by D-
STATCOM.(i.e Inductive mode)
III) Vt = Vsh –No reactive power exchange to the
active network.

3. International Journal of Emerging Technology and Advanced Engineering
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Fig 4- Operating Principal of D-STATCOM
IV. FUZZY LOGIC CONTROLLER SCHEME
The proposed model used fuzzy logic control as a
controller. Mamdani proposed FLC for a system has
number of input and output is only one. It is a
mathematical system dealing along to the probability and
soft computing provides. Fuzzy logic controller mainly
used for controlling of inverter action. It follows “if x and
y then Z” technique for getting solution of control
problem on the place of mathematically approach of the
system. Fig 5 shows the basic structure of FLC
Fig 5- Block Diagram of Control System
A)Estimation of Error- The error is estimated on the
difference among the bus voltage and reference
voltage. The rate of error is time rate of the error.
B)Fuzzification- Fuzzification is a process through
which the crisp quantities are changes into the
fuzzy, so the fuzzification process assign the
membership value of the crisp quantities. Triangle
membership function are used to the input and
output as shown in fig 6.
Fig 6- Membership Function of Input and Output
Error and rate of error are used to the linguistic
variable.
C) Fuzzy Rule Base- The linguistic variables that are
used are POS, POM, POB, NES, NEB, NEM and
ZE. The fuzzy process is based on Mamdani
method in this wok. The set of rules for controller
are shown in table. If then rule is used to describe
the base rule.
Table I
Rule Base of Fuzzy Logic
D) Defuzzification-The output of FLC is converted to
crisp value by using defuzzification process the
.The output of fuzzy can not be used as it is in the
application. So that conversion is must for the
further processing. This is done by defuzzification
method of centre of gravity.

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V. MODELLING OF PROPOSED SYSTEM
In this study D-STATCOM is proposed to enhance the
quality of power for the 11 kv distributed network.
System is composed of a feeder that transfer power to
distributed network at 50 Hz. The control strategy of the
system is shown in fig 7.
Fig 7- Flow Chart for Control Strategy
D-STATCOM is placed at the distribution end. The
simulation parameter are shown in Table II.
Table II-
Simulation Parameter
Proposed system are simulated 0n MATLAB 2012a
which is shown in fig
Fig 7-Simulink Model of Test System
VI. SIMULINK RESULT AND DISSCUSION
The test system are implemented for the various fault
conditions such as single line ground, line to line, double
line to ground, at various resistances.
Table III
Simulink Result
Various
Faults
Faults
Resista
-nces
System
Voltage(pu)
Without
DSTATCO
M
System
Voltage(
pu)
With
DSTAT
COM
%
Improve
ment
SLG 0.68 0.829 0.965 16.40
DLG 0.78 0.751 0.978 30.23
LL 0.88 0.817 0.992 21.42
TLG 0.68 0.671 0.935 39.34
The table II shows the simulated results of voltage in
pu for the various conditions. From the above results it is
clear that the voltage profile of the system improved.
TLG is most severe fault condition where the
compensation of sag is more to improve voltage profile.
Fig. 9 and fig. 12 shows system voltage value (pu) for
various fault conditions at various resistances as shown
in table II.
No System Values
01 Inverter IGBT based, 3 arm, 6 Pulse
Carrier Frequency= 1080 Hz
Sample time= 5µ second
02 Three
Phase
Transforme
r
Nominal Power=100 MVA
Frequency=50 Hz
Magnetization Resistance
Rm(pu)=500
Magnetization Induction
Lm(pu)=500
03 Load R=50 Ω
L=300e-3 H

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A)System Voltage Wituout D-STATCOM-
Fig 8- Voltage at PCC at SLG
Fig 9- Voltage at PCC at DLG
Fig 10- Voltage at PCC at LL
Fig 11- Voltage at PCC A TLG
B)System voltage with D-STATCOM- Fig 12 to fig 16
shows the voltage of system with D-STATCOM at
various fault and fault resistances. This is shows the
compensation of voltage sag in the power system
and voltage maintain within control.
Fig 12- Voltage at PCC at SLG
Fig 13- Voltage at PCC at DLG

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Fig 14- Voltage at PCC at LL
Fig 15- Voltage at PCC at TLG
VII. PERFORMANCE OF D-STATCOM WITH LCL FILTER
Fig 16- THD of Current without Filter
Fig 17- THD of Current with Filter
Fig 16 and fig 17 shows the TOTAL HARMONIC
DISTORTION (THD) for the current of D-STATCOM
without LCL filter /with LCL filter . THD is 43.43%
without filter although when filter is connected it’s
improved to 0.73%.
VIII. CONCLUSION
The result obtained by the simulation represents that
the mitigation is done for voltage sag by implementing
D-STATCOM in the power distribution system. In
addition to the fuzzy logic controller and LCL passive
filter with D-STATCOM, THD is very less and power
factor approximately close to the unity. Thus the power
quality of the power distribution can be improved. D-
STATCOM’s performance can be further improved by
applying intelligent optimization such as ANNs and
genetics algorithm.
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