Bidirectional DC-DC Converter With Zero Current Ripple and Low Voltage Stress for Power Battery Equalization Systems

Active equalizer is a significant approach to break through the inconsistent charging of power batteries, which can improve the available capacity, endurance mileage and system safety of the electric vehicles. As the important part of active equalizer, a bidirectional converter which possesses zero current ripple on the high voltage side (HVS) and small current ripple on the low voltage side (LVS), low voltage stress with wider conversion ratio, common ground and positive polarity between the LVS and HVS, is proposed in this paper. Therefore, with the proposed converter, the improved efficiency, speed and reliability of the active equalizer can be realized. The operating principles of the converter in boost mode to achieve cell-to-string (C2S) equalization and in buck mode to complete string-to-cell (S2C) equalization are analyzed. Besides, the detailed mathematical model and related simulations are presented to verify the feasibility and effectiveness of the proposed converter in the equalization system.