High-efficiency active cell-to-cell balancing circuit for Lithium-Ion battery modules using LLC resonant converter

A high-efficiency active cell-to-cell balancing circuit for Lithium-Ion battery modules is proposed in this paper. By transferring the charge directly from the highest voltage cell to the lowest voltage cell using an LLC resonant converter designed to achieve zero-voltage switching (ZVS) and nearly zero-current switching (ZCS) for all of the primary switches and zero-voltage zero-current switching (ZVZCS) for the diodes in the secondary, the proposed topology can achieve a high efficiency and a fast balancing speed with a simple control and design. In order to show the improved performance of the proposed method, a prototype circuit was built with a battery module having twelve Lithium-Ion (Li-Ion) batteries. Experimental results are presented to verify the shorter balancing time and higher efficiency of the proposed method when compared with conventional methods. The measured time for the balancing of the twelve cells was 47 min and a maximum efficiency of 94.5% was achieved at 1.5 W.