A Novel Transfer Switch and Control Strategy for Dual Input Power Supplies of Three-phase Electric Motor

In ship field, to ensure reliable operation of three-phase electric motor, two redundant input power supplies are generally equipped, one works as main power and the other as hot redundancy. When the main power fails, the input power of the motor should smoothly transfer to the standby power. During the transfer process, a comparatively large phase difference between the electromotive force and the standby power supply will cause large surge current far exceeding the direct start-up current of the motor, which will severely damage the motor and shorten its lifetime, so is the case when switching back after troubleshooting. In this paper, a novel transfer switch is proposed with its control strategies detailedly illustrated. This switch could limit the voltage difference within the rated voltage of the motor and meanwhile limit the phase difference within 60°, so the surge current won’t exceed the direct start-up current of the three-phase asynchronous machine. Its effectiveness is verified by experiments carried out on a 10kVA prototype.