21-01-2013, 12:46 PM
Performance Comparison of PID and Fuzzy Control Techniques in Three Phase Induction Motor Control
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Abstract
The demand for control of electric power for electric
motor drive system and industrial control exists since many
years. Variable-speed drives are designed when a motor is
combined with a power electronics converter. By introducing
variable speed for the driven load, it is possible to optimize
the efficiency of the entire system and this is the area where
the maximum efficiency gains are possible. The closed loop
control strategies employed are legion and PID is seemed to
be superior amongst them. However it further needs to be
improved in terms of overshoot and settling time. So control
strategies based on soft computing could be good alternative.
This paper describes the implementation of controllers based
on PID and Fuzzy Logic strategies. A comparative performance
analysis demonstrates that the clever exploring of Fuzzy Logic
control strategies circumvents the demerits of PID control
strategies.
INTRODUCTION
AC motors are more popular with their integration in large
number of applications like pumps, conveyors, machine tools,
centrifugal machines, presses, elevators, and packaging
equipment etc. The major benefits of using AC motor in a
system are improved reliability, better performance, higher
efficiency, easy scalability and feasibility of speed and torque
control by different techniques. The techniques such as Rotor
Resistance Control, Stator Voltage Control, Variable f, V/F
Control, Slip Energy Recovery Scheme etc. play significant
role in precisely controlling the speed of motors. Many researchers
have reported the work on speed control of AC
machines employing different control strategies [1-3]. The
performance comparison of various drives reported in literature
help the comprehensive understanding the drive option
targeted for application of interest [5, 11, 13]. An induction
motor supplied by an ac drive can operate over a good range
of frequency, typically from 10Hz to 90Hz.
Three Phase Inverter Design
Three phase inverter designed using power MOSFETs is
as shown in fig.2. The inverse diode associated with the
device is sufficient to operate the circuit at higher frequencies.
MOSFET technology promises to use much simpler and
efficient drive circuits with significant cost benefits compared
to bipolar devices. High voltage capacitor is connected across
the rectifier out to provide low impedance path for high
frequency current at switching of power devices.
PID Controller Simulink Design in MATLAB
PID Tuner provides a fast and widely applicable singleloop
PID tuning method for the Simulink PID Controller blocks.
With this method the PID parameters can be easily tuned to
achieve a robust design with the desired response time. The
actual speed of motor is sensed by speed sensor using PIC
controller and it sent serially to Simulink. As shown in fig.5
the Simulink block corresponding to constant is used to set
desired speed. Here auto tune PID is used for tuning plant or
system. The transfer function of motor system is a second
order type that exhibits overshoot and large settling time
which forms the metrics of performance in the present study.
RESULTS AND DISCUSSION
Designing a suitable controller for three phase induction
motor is a challenge. In practice non fuzzy control algorithms
seems to be doing better on commercial level, yet scope exits
to develop the newer control techniques based on soft
computing. PID and FUZZY controllers are very efficient for
speed controlling of three phase ac induction motor.