Cascaded H-bridge converter (CHBC) is a popular approach for massive battery energy storage system (BESS) connected to the medium-voltage grid. However multi-objective needs, including power control, state of charge (SOC) control, fault tolerant control and so on, makes the control system complicated. A unified control scheme is proposed in this paper. By evaluating the other control objects and power redistribution, the control system is simplified and the calculation result of zero-voltage is much clearer. In the end, a simulation model based on Matlab/Simulink is created and a 30kW laboratory prototype is built. The simulation and experimental results verify the feasibility of the proposed control scheme.