Rapid Soft Re-switching Technique of Three-phase Induction Motors and Its Initial Transient Analytical Method

If the induction motor could keep rotating near rated speed or synchronous speed after power supply is lost for a short time, the re-switching dynamic behavior presents as brief electromagnetic transient. The rapid soft re-switching technique on base of power electronic switches could realize the re-switching rapidly without the inrush current within 0.1 s, which control strategy is different from soft start aimed at longer electromechanical transient. In order to realize the rapidity of soft re-switching, the analytical method is applied to deduce the relationship between transient current and firing angle. As for the transient course that two phase windings connecting and three phase windings connecting are alternated each other, the reduced unbalanced transient model in αβ0 reference frame and the balanced transient model expressed with space vector are established respectively. So the analytical solution could be simplified and the initial firing angles are determined rapidly. Finally, the complete rapid soft re- switching control strategy composed of sequence of firing angles is verified with the simulation and experimental results.