LIMITING STATOR CURRENT FOR THREE-PHASE INDUCTION DRIVE MOTOR USING PULSE WIDTH MODULATION SYSTEM

Summary

Induction motor is the most widely used electromechanical machine due to its low cost and minimum
maintenance. It has more losses, less efficiency and high power consumption when working at variable speed.
The influence of these motors (in term of energy consumption) in energy intensive industries is significant in
total input cost. This research presents a development of optimal control system for induction motor drives
using pulse width modulation system leading to optimization of the stator current to its least possible value for a
given output torque and energy saving. The stator voltage values of the induction motor was varied by varying
the modulation index (Ma) using the principle of constant flux. The classical optimal control system which uses
information on torque of the motor was used to generate the appropriate voltage amplitude that minimized the
induction motor stator current. The constant optimal stator current controller models were configured and built
for a set of experimental data using MATLAB computer program. The models were validated by simulation
using a typical three-phase induction motor of 4000kw, 400V at a nominal frequency of 50Hz drive model
implemented with MATLAB/Simulink toolbox. The results show that at minimum torque, the initial current
needed to operate the induction motor at nominal frequency using the open loop system was 3.6A but using the
classical control, 1.6A was needed to operate the induction motor saving 2.0A. The results show greater stator
current minimization when implementing classical optimal control system.

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