Torque close-loop control of a novel soft starter of induction motor

This paper describes a novel topology of soft starter for induction motors. Unlike the thyristerized soft starter, the proposed circuit configuration utilizes the self-commutated device to replace the thyristor as the switch on the supply line. The operating principle of the control system is analyzed. The transient process during starting has been studied using a presented mathematical model which is general enough to simulate most of the ac chopper control system as applied to induction motors. The dynamic performance of starting current and torque pulsations can be improved by the simple control strategy, which is the duty cycle of switches is regulated by PI controller. The experimental setup, which is realized with a controller based on the DSP, is presented. The corresponding experimental results obtained for a squirrel-cage induction motor prove the validity of the proposed soft starter.