Download enhancement of power quality using d-statcom based on

ENHANCEMENT OF POWER QUALITY USING D-STATCOM BASED
ON FUZZY LOGIC
G. Sathish Goud1, K. Srujana Reddy2
1Assistant
2Student
professor, Electrical Engineering, SIET, Telangana, India
M.Tech, Electrical Engineering, SIET, Telangana, India
ABSTRACT: A Power quality problem is
harmonics. Voltage dips are considered to
an occurrence manifested as a nonstandard
voltage, current or frequency that results in
a failure or a misoperation of end user
equipments. Utility distribution networks,
sensitive industrial loads and critical
commercial operations suffer from various
types of outages and service interruptions
which can cost significant financial losses.
With the restructuring of power systems
and with shifting trend towards distributed
and dispersed generation, the issue of power
quality is going to take newer dimensions.
This paper presents the enhancement of
voltage sags/swell; harmonic distortion and
low power factor using Distribution Static
Compensator (D-STATCOM). The model is
based on the Voltage Source Converter
(VSC) principle. The D-STATCOM injects
a current into the system to mitigate the
voltage sags/swell. To improve harmonic
distortion and low power factor. The
simulations
were
performed
using
MATLAB SIMULINK version R2009b.
be one of the most severe disturbances to
the industrial equipment. 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 sag and swell. These power quality
devices are power electronic converters
Connected in parallel or series with the
lines and the operation is controlled by
digital controllers. The modelling of these
complex systems that contains both power
circuits and control systems can be done
different bases. In present extension
concept change in the control technique
i.e., in place of PWM technique
using
fuzzy logic controller to increase the
Keywords- D-STATCOM, Total harmonics
Distortion (THD, Voltage Sag/swell, and
Voltage Source Converter (VSC).
stability of a voltage. STATCOM is one of
the facts devices it can below to reduce
reactive
I.
INTRODUCTION
power
and
power
quality
problems and increases the efficiency of
Now days, modern industrial devices are
the
mostly based on the electronic Devices
technique. The DST ATCOM helps to
such as programmable logic controllers
improve the power factor and eliminate the
and electronic drives. The electronic
Total Harmonics Distortion (THD) drawn
devices are very sensitive to disturbances
from a Non-Liner Diode Rectifier Load
and become less tolerant to power quality
(NLDRL).
problems such as voltage sags, swells and
system
by
using
fuzzy control
II.
system cost in general, a CSC derives its
D-STATCOM
The STATCOM is the solid-state-
based power converter version of the SVC.
Operating as a shunt-connected SVC, its
capacitive or inductive output currents can
terminal power from a current source, i.e.,
a reactor.
Control Strategies:
be controlled independently from its
Satisfactery, performance, fast resp
connected AC bus voltage. Because of the
onse, flexible and easy implementation are
fast-switching characteristic of power
the Main objectives of any compensation
converters, the STATCOM provides much
strategy. The control strategies of a D-
faster response as compared to the SVC. In
STATCOM are mainly implemented in the
addition, in the event of a rapid change in
following steps:
system voltage, the capacitor voltage does
not change instantaneously; therefore, the
STATCOM effectively reacts for the
desired responses. For example, if the
system voltage drops for any reason, there
is a tendency for the STATCOM to inject
capacitive power to support the dipped
voltages
.Theoretically,
the

Measurment of system Variables
and signal conditioning

Extraction
of
compensating signals

Generation of firing angles for
switching devices
power
converter employed in the STATCOM can
be either a VSC or a current-source
converter (CSC).
In practice, however, the VSC is
preferred because of the bi directional
voltage-blocking capability required by the
power semiconductor devices used in
CSCs. To achieve this kind switch
characteristic, an additional diode must be
connected in series with a conventional
semiconductor switch, or else the physical
structure of the semiconductor must be
Fig.2.1 Schematic diagram of D-
modified.
STATCOM control
Both
of
these
alternatives
increase the conduction losses and total
reference
The generation of proper pulse width
modulation (PWM)
for Dc-bus voltage control. Through
firing is the most
experimentation we have built a rule base
important part of D-STATCOM control
which is used by the fuzzy logic controller
and it has a great impact on its
for robustness in controlling voltage. We
compensation objectives, transient as well
defined fuzzy subsets for inputs error
as steady state performance harmonic
signal and changes in the error signal. The
elimination. This paper is an attempt to
representation of fuzzy logic controller is
compare the following schemes of a D-
as shown the process of fuzzy reasoning is
STATCOM for power factor correction
incorporated into what is called a Fuzzy
and harmonic mitigation based on:
Inference System. It Is comprised of three
1. Phase shift control
2. Indirect decoupled current control
3. Regulation of AC bus and DC link
voltage. The performance of D-
steps that process the system inputs to the
appropriate system outputs. These steps
are 1) Fuzzification, 2) Rule Evaluation,
and 3) Defuzzification.
STATCOM with different control
schemes have been studied through
digital simulations for common
system parameters, as given in the
Appendix.
III.
FUZZY LOGIC
CONTROLLER
Fig.3.1 Fuzzy logic controller
Fuzzy logic controller is widely used in
controlling disturbances in power systems.
The other controller known as PI controller
is not efficient for many reasons. They
include its inability to withstand abrupt
changes in error signal, and it is not
dynamic in determining the present error
signal. In this paper we proposed the usage
of fuzzy logic controller in order to
improve the performance of STATCOM
The fuzzy logic controller has
certain
components
fuzzification,
knowledge
inference
and
known
base,
as
fuzzy
defuzzification.
Fuzzification takes input and then fuzzy
inference makes use of knowledge base
and processes its logic accordingly while
defuzzification produces required output.
IV.
SIMULATION AND RESULTS
A program is developed to simulate
the both PI controller based and fuzzy
logic based D-STATCOM in MATLAB.
The complete D-STATCOM system is
composed mainly of three-phase source, a
nonlinear load, a voltage source PWM
converter, and a fuzzy controller or a PI
controller. All these components are
modelled separately, integrated and then
solved to simulate the system.
Fig.4.2. Compensating current and Reactive
power of D-STATCOM with Fuzzy Logic
Control
The mitigation of load voltage sag
with D-STATCOM. To mitigate the
voltage sag in load side, D-STATCOM has
to inject the compensating reactive i.e.,
leading reactive power (Capacitive) in the
system as shown in figure 4.1 and 4.2. And
Fig.4.1. Compensating current and Reactive
power of D-STATCOM with PI Control
can be see that the reactive power
compensated by fuzzy logic controller is
much faster and also smoother than
conventional controller. The mitigated sag
in voltage with conventional controller
takes 8 cycles to reach steady state with
%THD in load voltage of 4.71% whereas
the proposed controller (Fuzzy Logic
Control) takes 5 cycles to reach steady
The mitigation of load voltage
state with % THD in load voltage of
swell with D-STATCOM. To mitigate the
2.91%.
voltage sag in load side, D-STATCOM has
to inject the compensating reactive i.e.,
lagging reactive power (Inductive) in the
system as shown in figure 4.3 and 4.4. And
can be see that the reactive power
compensated by fuzzy logic controller is
much faster and also smoother than
conventional controller. The mitigated
swell
in
voltage
with
conventional
controller takes 4 cycles to reach steady
state with %THD in load voltage of 3.95%
whereas the proposed controller (Fuzzy
Logic Control) takes 3 cycles to reach
Fig.4.3. Compensating current and Reactive
power of D-STATCOM with PI Control
steady state with % THD in load voltage of
2.84%.
Finally D-STATCOM is tested
with dynamic load where both active and
reactive power varying form 770 kW to 0
W and 440 kVAR to 0 VAR (peak to
peak) respectively at a frequency of 15 Hz
at an average of 385 kVAR and 220 kW as
shown in Figure 7.11. The D-STATCOM
with fuzzy logic control shows fewer
oscillations
in
magnitude
and
error
tolerance than conventional controller.
CONCLUSION
Fig.4.4. Compensating current and Reactive
power of D-STATCOM with Fuzzy Logic
Control
1)
This paper has presented the power
quality problems such as voltage sags and
swell. Compensation techniques of custom
power electronic device D-ST ATCOM
[3] H. Hingorani, "Introducing custom
was presented. The design and applications
power", IEEE Spectrum, vol. 32, no.6, pp.
of D-STATCOM for voltage sags, swells
41-48, June 1995.
and comprehensive results were presented.
[4] N. Hingorani, "FACTS-Flexible ac
transmission systems," in Proc. IEE 5th Int
2)
The
Voltage
Source
Convert
Conf AC DC Transmission, London, U.K.,
(VSC) was implemented with the help of
1991, Conf Pub. 345, pp. 1-7.
FUZZY CONTROLLER. The control
[5]
scheme was tested under a wide range of
"Modeling analysis and soltion to power
operating conditions, and it was observed
quality problems," unpublished.
to be very robust in every case. For
[6] G. Venkataramana, and BJohnson, "A
modelling and simulation of a D-ST
pulse
ATCOM by using the highly developed
conditioner for sensitive load centers,"
graphic
IEEE Trans. Power DeliVary, vol. 12, pp.
facilities
available
in
MA
TLAB/SIMULINK were used.
Mahesh
width
Singh,
Vaibhav
modulated
Tiwari,
power
line
844-849, Apr. 1997.
[7] L Xu, O. Anaya-Lara, V. G. Agelidis,
3)
The simulations carried out here
and E. Acha, "Development of prototype
showed that the D-STATCOM provides
custom power devices for power quality
relatively
enhancement," in Proc. 9th ICHQP 2000,
better
voltage
regulation
capabilities
Orlando, FL, Oct 2000, pp. 775-783.
REFERENCES
[I] O. Anaya-Lara, E. Acha, "Modeling
and analysis of custom power systems by
PSCAD/EMTDC," IEEE Trans. Power
Delivery, vol. 17, no .I, pp. 266-272,
January 2002.
[2] S. Ravi Kumar, S. Sivanagaraju,
"Simualgion of D-Statcom and DVR in
power
system,"
ARPN
jornal
of
engineering and applied science, vol. 2, no.
3, pp. 7-13, June 2007.