A high efficiency Zero Voltage-Zero Current Transition converter for battery cell equalization

This paper proposes a new ZVZCT (Zero Voltage Zero Current Transition) dc/dc converter for voltage equalization in series connected battery cells. The proposed circuit equalizes the battery cells by principle of voltage-second balance of inductor and transformer coupling. By adding auxiliary resonant cells at the main switching devices such as MOSFET or IGBT, zero current switching is achieved and turned off loss of switching elements is eliminated. In the other hand, zero voltage switching can be applied to switching elements by the voltage/second balancing of the inductor. Transformer coupling between battery cells and ZVZCT switching method allows the fast balancing speed and high frequency operation, which reduces size and weight of the circuit. The validity of the battery equalization is further verified using prototype board involving four lithium-ion battery cells. The experiment result shows that the proposed ZVZCT battery equalization scheme can achieve faster equalization speed and increase the efficiency compare with the conventional battery equalization schemes.