Improvement in the performance of induction machine by using fuzzy logic based direct torque control

This paper compares fuzzy logic controller with conventional PI controller based direct torque control (DTC) for an induction motor. The voltage controlled gating pulses to inverter are of variable frequency by using carrier based PWM with reference to sinusoidal waveform to achieve desired results. The torque and flux estimation block and speed error control block are the heart for this control system. The analysis is developed by using MATLAB/ SIMULINK. The proposed fuzzy based technique is smooth torque transform and maintains desired torque even though there is change in speed or vice-versa. The system stability can be improved by using FLC than PI controller, even under sudden changes in speed and torque of the machine. The torque ripples were less for both PI and FLC based controller scheme compared to previous techniques. Torque surges due to sudden change in speed of machine can also be minimized by using proposed fuzzy controller scheme. The comparisons of PI with FLC were studied under 2 cases, in 1st case, constant speed and variable torque and 2nd case, variable speed and variable torque.