Current limiting soft starter for three phase induction motor drive system using PWM AC chopper

Abstract

This study presents a new current-limiting soft-starter for a three-phase induction motor drive system using pulse width modulation (PWM) AC chopper. A novel configuration of three-phase PWM AC chopper using only four insulated gate bipolar transistors (IGBTs) is also proposed. The proposed control strategy does not require zero crossing detection circuits, which employed in thyristorised soft starters. It requires only one current sensor. The duty ratio of the chopper IGBTs is obtained from the closed-loop current control in order to limit the motor starting current at a preset value. Only two complementary gate pulses are obtained from the control circuit to control the four IGBT switches. The proposed control strategy is characterised by a simple control loop; thus, a low-cost processor can be used due to the low-computation burden. The superiority of the proposed strategy is proved theoretically and confirmed experimentally. The experimental work is developed using a laboratory prototype system composed of DSP-DS1104 digital control board and 1.5 HP induction motor. The proposed starter offers a smooth start-up for the motor speed, torque ripple minimisation, less number of semiconductor switches, less switching and conduction losses, less harmonics and improved input power factor.