Seamless Switching Control Strategy for Diesel Generator and Energy Storage Hybrid Emergency Power Supply System

The hybrid emergency power supply system composed of a diesel generator and a battery energy storage system(BESS) will complete seamless switching from power grid to BESS at the moment of power grid failure. After a short term power supply BESS needs to transfer power to the diesel generator. In order to ensure the quality of power supply during switching process, seamless switching from BESS to diesel generator is needed. In this paper, the constant voltage and constant frequency control strategy is proposed to stable the frequency and amplitude of the output voltage when BESS works separately. After the diesel generator is put into operation, it provides stable voltage amplitude and frequency support for stand-alone system, therefore, only the power control of the converter is needed, and the output power is gradually reduced according to the reference value of the given power. Then the load is transferred to the diesel generator gradually, and seamless switching from BESS to the diesel generator is completed. The simulation model of the seamless switching process of the hybrid emergency power supply system is built in this paper. In view of the difference between amplitude and frequency of diesel generator voltage and their rated values in the quasi synchronization grid connection, a control strategy for timely switching control mode is worked out. The simulation results show that the control strategy can ensure the uninterrupted power supply for the load and the seamless switching from BESS to the diesel generator.