A Multi-winding Transformer Cell-to-Cell Active Equalization Method for Lithium-Ion Batteries with Reduced Number of Driving Circuits

The bidirectional cell-to-cell equalization methods perform well to prevent the series-connected batteries from overcharging and undercharging. However, it remains a challenge to achieve fast equalization and high equalization efficiency with low complexity. To address the issue, we propose a new bidirectional cell-to-cell active equalization method using a multiwinding transformer. The new method allows the energy to transfer directly from the highest voltage cell to the lowest one by fly-back operation or forward operation which gives a short balancing path and guarantees a fast equalization speed. We adopt the bidirectional switches of low conduction loss for high equalization efficiency. Since the bidirectional switches are turned on or off simultaneously, a common driving circuit for the bidirectional switch has been designed to reduce the number of the driving circuits by half. The experiments with a six 50-Ah Lithium-ion battery strings are conducted and the results have demonstrated that our new approach has achieved a good overall performance of equalization in terms of speed, efficiency, and complexity of the circuit.