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Abstract
Ac motor drives are used in a multitude of industrial and process applications
requiring high performances. In high-performance drive systems, the motor
speed should closely follow a specified reference trajectory regardless of any
load disturbances. The motor-control issues are traditionally handled by fixed-
gain proportional-integral (PI) and proportional-integral-derivative (PlO)
controllers. However, the fixed gain controllers are very sensitive to load
disturbances. In order to overcome this problem, the fuzzy-logic controller
(FLC) has been recently used for motor control purpose. The mathematical tool
lor the FLC is the fuzzy set theory introduced by Zadeh. It is based on the
linguistic rules with an IF-THEN general structure, which is the basis of human
,
logic. However, the application of FLC has faced some shortcomes during
hardware and software implementation due to its computational burden.
Some calculation programs have been developed to determine the
voltage and frequency which should be applied to the motor to enable it to run
at constant speed with variable loads, or variable speeds with constant load, or
variable loads, with variable speeds. The outputs of these programs are fed to
the Sugeno-type fuzzy inference to estimate its output (voltage or frequency or
both) if it is excited by its inputs (torque or speed or both).
Two models has been designed to perform the closed-loop fuzzy
controller system for inverter fed three phase induction motors. The model is
distinguished according to the inputs of the fuzzy logic controller.
The speed error (Aro) and the rate of change of speed error (~ffi/~t) are
considered as the input linguistic variables and the motor frequency IS
considered as the output linguistic variable for the first model. Two different
techniques were developed to accomplish this model. In the first technique, the