Soft started induction motor modeling and heating issues for different starting profiles using a flux linkage ABC-frame of reference

In order to mitigate adverse effects of starting torque transients and high inrush currents in induction motors, a popular method is to use electronically controlled soft starting voltages utilizing series connected silicon controlled rectifiers (SCRs). Investigation of semi-optimum soft starting voltage profiles was implemented using a flux linkage ABC-frame of reference model of a soft started three-phase induction motor. A state-space model of the soft starter thyristor switching sequence for the motor and load was developed and implemented in a time-domain simulation to examine winding heating and shaft stress issues for different starting profiles. Simulation results of line starts and soft starts were compared with measured data through which validation of the model was established. In this paper, different induction machine soft start profiles are shown and comparisons of starting times, torque profiles, and heating losses are made. Discussion of these results and conclusions as to the near-optimum types of profiles are delineated based on peak torque, starting times, and winding heating criteria.