SSTS-based soft transfer control method of motor load under different residual voltage condition

For critical load supplied with dual power source, solid state transfer switch (SSTS) is usually employed to realize rapid bus transfer. A SSTS-based soft transfer control method is proposed in this paper to suppress the inrush current when the load driven by motor is switched onto alternate source. The research focus on concrete soft transfer control strategy and how to recalculate firing angles of SCRs considering phase angle difference between alternate source and the residual voltage of motor at the time of transferring after power-off. Both simulation and test of soft transfer prove that the effect of suppressing inrush current is distinct. The validity of the method is verified by more typical test results under different residual voltage condition.