Designing Electric Vehicle Battery Charging

A pioneering technology for electric vehicle power converters is the double-star modular multilevel converters with embedded battery cells. In this topology, the battery cells are connected in series via half bridge DC–DC buck converters, enabling independent discharge and recharge. This paper presents a novel control system designed specifically for this converter topology. The proposed control system aims to charge the battery cells from the grid at unity power factor while simultaneously balancing their state of charges, all without impacting grid voltages and currents. The grid current controller is developed and implemented in the stationary reference frame using a proportional-resonant controller. Meanwhile, the state of charge balancing algorithm is designed using a sorting algorithm and circulating current control. Simulation and experimental results validate the effectiveness of the proposed control strategy. They demonstrate that the strategy can charge the battery cells with minimal distortion of the grid current and ensure cell balance during recharge without affecting grid current.