The rapid soft re-switching technology of three-phase induction motors

For induction motor rotating near the synchronous speed, re-switching of power supply could be realized by rapid soft re-switching technology which could eliminate or reduce the inrush current and torque. The intelligent hybrid switches(IHS) based on SCRs is used to implement the control strategy of rapid soft re-switching with series of firing angles. Aiming at the alternating state of soft re-switching transient current, the unbalanced model of three-phase induction motor is established in alphabeta0 reference frame for two phase windings connected, and the balanced model is presented with space vector for three phase windings connected. By means of the analytical method, the relationship between the initial half-wave peak value of transient current and initial firing angles of SCRs is given and the speed influencing is studied. After the initial firing angles are determined, the subsequent firing angles are obtained with even step length which could be calculated at given speed. Finally, the control strategy of rapid soft re-switching with series of firing angles is validated by numerical simulation and experimental results.