Performance Enhancement of Field Oriented Induction Motor Drive System

Abstract

This research focuses on the performance enhancement of an indirect field oriented (IFO) induction motor drive system by designing an efficient controller for speed regulation and by maintaining optimal operation of a three phase inverter. The most widely used techniques for three phase inverter operation are the space vector pulse width modulation, the sine triangle pulse width modulation (SPWM) and square wave mode of operation. The first objective of this research work is to design a synchronous SPWM technique with minimal total harmonics distortion (THD). SPWM performs better at low speed due to lower harmonics in the frequency spectrum, while square wave mode is beneficial at high speed operation because of its higher DC bus utilization. The inverter mode of operation is switched from SPWM to square wave when the motor operates above the base speed for higher DC bus utilization. The sudden inverter mode switching results in unwanted torque ripples and therefore degrades the speed controller performance. Thus the second objective of this work is to design a mode switching strategy which ensures a torque ripple free transition. The speed regulator performance enhancement is the third main objective of this work. Conventionally, a linear integer order proportional integral (IO-PI) controller regulates the motor speed. However, the fractional order proportional integral (FO-PI) controllers have been documented to perform better than IO-PI controllers due to their Iso-damping property. Therefore, in this work the performance of a nonlinear FO-PI controller is compared with integer order controllers such as Ziegler-Nichols proportional integral (ZN-PI) controller, Cohen-Coon proportional integral (CC-PI) controller and a proportional integral controller tuned via trial and error (TE-PI) method are designed. Simulation and experimental investigation proves that FO-PI controller has better speed tracking, less settling time, exhibits better disturbance rejection and low speed tracking and can even control a detuned motor's speed very well.