This paper analyzes the main topologies and mathematical model of Power Conversion System, called PCS, and also studies its control strategy. The two-stage charging model, first constant current charging to the rated voltage and then transferred to constant voltage charging, is used to ensure the safety of storage battery and prolong the service life. In order to avoid the shortages of the traditional charge and discharge control method, the unified control strategy of charging and discharging is proposed, based on that, grid-side and battery-side converters are respectively designed to work in passive and active power control. The simulation and experimental results are consistent with the theoretical analysis, the converter achieves good dynamic and static performance, control requirements.