Soft starter inside delta motor modeling and its control

The paper presents a simulation of a thyristor based reduced voltage starter operating inside a delta connected induction motor. Behavior of the reduced voltage starter is shown to be different when operated inside the delta than when operated in the ac lines. Simulations of conventional control strategies based on delay of firing from voltage zero crossings (alpha control) and delay of firing from current zero crossings (gamma control) are presented and control problems are described. A control strategy based on combining these two methods is presented, along with a simplified current limit control algorithm.