7/28/2019 06007190
1/7
Performance Comparison of a Robust Self Tuned
Fuzzy Logic Controller used for Power Control in
Wind Conversion SystemsSwagat Pati K.B.Mohanty Benudhar Sahu
Department of Electrical Engineering Department of Electrical
Engineering Department of Electrical Engineering
National Institute of Technology National Institute of
Technology National Institute of Technology
Rourkela, India Rourkela, India Rourkela, India
[email protected] [email protected]
[email protected]
Abstract In this paper a line excited cage generator is
consideredwhich is connected with the grid through a bidirectional
PWM
converter- inverter system. The generator is controlled by
indirectfield oriented control (IFOC) scheme. Fuzzy logic
controllers (FLC)
are used for the control purpose. The first FLC is used in the
outerspeed loop to track the generator speed with the reference
speed for
maximum power extraction and the second and third FLCs are
usedin the inner current loops for control of active and reactive
power.
The FLCs use normalized values of error and change of error as
theirinputs. The outputs of the FLCs are again multiplied with
gains togive the control signals. A trapezoidal membership function
is takenfor the error input and triangular membership functions are
taken for
change of error as well as output.Again a robust self tuned
fuzzy logic controller (STFLC)
scheme is used in place of the FLCs. In this scheme a tuning
FLC(TFLC) is used to tune the output gain of the main FLC. The
inputs
to both the FLCs are normalized values of error and change of
error.The output of the TFLC is the output gain of the main FLC.
The main
FLC is similar to the FLC as discussed in the previous scheme.
In theTFLC triangular membership functions are used for all input
as well
as output variables. The performances of both the schemes
aresimulated and a comparison is given. The simulation work is done
in
MATLAB coding environment.
Keywords-Induction Generator, Bidirectional PWM inverter,
Fuzzy
Logic Controller, Self Tuned Fuzzy Logic Controller,
Indirect
Vector Control.
I. INTRODUCTION
In last 100 years, the human civilization has gone too
far in exploiting the limited resources on earth making the
biosphere vulnerable to many uncertain large scale
disasters.
Many of such crises is due to the limited resource for the
generation of electrical power. In the past three four
decadesharnessing hydro/wind energy for electric power
generation
and the possible such alternate system is developed. A
continuous research is going on taking into account
different
critical issues in this sector. Wind energy is one of the
mostimportant and promising source of renewable energy all over
the world, mainly because it is considered to be nonpollutingand
economically viable. At the same time there has been a
rapid development of related wind energy technology.
However in the last two decades, wind power has been
seriously considered to supplement the power generation by
fossil fuel and nuclear methods.
Normally induction machines are used for generation
purpose in wind energy systems, among which the cageinduction
machines are well known for their advantages.
These machines are relatively inexpensive, robust, and
requirelow maintenance. But due to the coupling effect between
active and reactive power the response becomes sluggish and
the control becomes difficult and complex in case of
induction
generators. Because of this there arises stability problem
when
the system is connected with the grid. When induction
machines are operated using vector control techniques, fast
dynamic response and accurate torque control are obtained.
All of these characteristics are advantageous in variable
speed
wind energy conversion systems (WECS). Squirrel cage
generators with shunt passive or active VAR (volt ampere
reactive) generators was proposed in [3], which generate
constant frequency power through a diode rectifier and line
commutated thyristor inverter. Operation of several selfexcited
induction generators connected to a common bus is
analyzed in [4]. The control systems for the operation
ofindirect rotor flux oriented vector controlled induction
machines for variable speed wind energy applications are
discussed in [5]-[7]. Sensorless vector control scheme
suitable
to operate cage induction generator is discussed in [5]. In
[6]
cage induction machine is considered and a fuzzy control
system is used to drive the WECS to the point of maximumenergy
capture for a given wind velocity.
The induction machine is connected to the utility
using back to-back converters. In this paper a variable
speed
wind turbine driven squirrel cage induction generator system
with two double sided PWM converters is described.
Fuzzycontrollers are used to optimize efficiency and enhance
performance. Again a self tuned fuzzy logic control scheme
is
implemented for performance enhancement purpose and a
comparison is given. The control algorithms are evaluated by
MATLAB simulation study.
II. INDUCTION GENERATOR MODEL
The basic configuration of a line excited induction
generator is sketched in Fig.1. Normally the stator is
interfaced with the grid through back-to-back PWM inverter
Modern Electric Power Systems 2010, Wroclaw, Poland MEPS10 paper
07.6http://www.meps10.pwr.wroc.pl
