Speed control for a three-phase induction motor using V.V.V.F. techniques

Abstract

The aim of the project/ thesis is to design the control circuits and equipment necessary for controlling the speed of a three-phase induction motor by using a variable voltage, variable frequency method of speed control. Although many variable voltage, variable frequency speed control methods exist, pulse-width modulation techniques are adopted for speeds below and up to base speed, i.e. 1500 r.p.m. while notched square wave operation is implemented above base speed. A stiff d.c. voltage is supplied to the voltage source inverter (preferred from the current source inverter) by means of a three-phase uncontrolled bridge rectifier whose output is filtered by means of a large capacitor. The voltage source inverter has MOSFETs as its switching elements. MOSFETs were preferred from other components for their improved safe operating region and other advantages.