A Modular Three Phase AC Voltage Controller for Induction Motor

Abstract

Three phase induction motor (IM) is widely used in the industries because of rugged construction. User needs to control speed of the motor depending on the desired speed and application. In this paper launching of speed control of 3-phase IM is controlled by 3-phase AC voltage controller by varying the voltage by pulsewidth modulation (PWM) technique. In olden days speed control was possible for DC motors only, but with the presence of power electronics converters such as AC regulators, inverters and cycloconverters, it has become possible to control the speed of induction motors. These days regulating the stator source voltage at a constant frequency is one of the modern and low cost methods in order to control the speed of induction motors near its nominal speed. The speed control of IM by 3-phase inverters, cycloconverters require forced commutation circuit, which is complicated and these presents high surge currents and surge voltages. But AC voltage controller makes use of line commutation and as such no complex commutation circuitry is required in this controller. The main application of this model is fan drives, domestic pump and industrial applications.