High efficiency active cell balancing circuit with soft-switching technique for series-connected battery string

This paper proposes a high efficiency active cell balancing circuit for series-connected battery strings. The proposed circuit consists of a multi-winding transformer, a diode, and bi-directional switches having the same number of cells in the target battery string. This circuit balances the voltage of each cell in the battery string, and is designed to achieve the soft switching for the reduction of the switching loss of circuit. The PSpice simulation and experiment are implemented to verify the feasibility and effectiveness of the proposed circuit. In the case that the balancing charges are transferred from the higher voltage cell to the lower voltage cell, the simulated and measured power efficiency of the proposed circuit are 85 % and 86.3 %, respectively.