The torque oscillation study in the motor soft starting process with discrete variable frequency method

The starting current is big and the torque is small when the motor begins to start with the nominal voltage .The discrete variable frequency method can solve the above two questions, at the same time brings the torque oscillation.The paper analyses the cause in detail, and then presents the solved method: the combination between discrete variable frequency method improvement and power factor closed loop control.The simulation model is set up, and its simulation result proves that the method can diminish the torque oscillation and demonstrates that the method is valid and feasible.