Soft starting control scheme for three-phase induction motor fed by PWM AC chopper

This paper presents a soft starting control scheme of a three-phase induction motor using a PWM AC chopper technique to reduce the magnitude of currents during a start up process. To control bidirectional power switches in the PWM AC chopper, a PWM signal is generated by a single voltage signal, and compared with a single carrier signal. By this approach, the PWM signal is independent since the PWM signal does not need to be synchronized with three-phase voltages from a source. Details of the control scheme are discussed. Simulation results of the starting currents using this control technique are shown, and it is found that the control scheme can be employed in the PWM chopper in order to limit the amplitude of the starting currents.