Oscillation in soft-starting of induction motor

Oscillation of current, electromagnetic torque and speed appears during soft-starting of three-phase induction motor. According to the mathematical model of the induction motor, a common simulation model of induction motors is established. Some influencing factors of the oscillation are analyzed and the cause of oscillation is derived. In addition, a method of controlling hold-off angle is proposed. This method makes the current zero-crossing as the reference. During the starting process of induction motor, the hold-off angle of current has gradually decreased from initial value to zero. This paper verifies the correctness of the method by simulation. Furthermore, it presents experimental facility based on hold-off angle control and experiments on a prototype induction motor. Then experiment results validate the correctness of theory analyses.