Switched capacitor with chain structure for cell-balancing of lithium-ion batteries

In rechargeable batteries such as lithium-ion, the cell balancing circuit is necessary to enhance life time and guarantee safety. Switched capacitor circuit is a cost-effective and simple cell balancing method, but it shows the prolonged balancing time caused by a cell-to-cell energy shift. Therefore, this paper proposes switched capacitor with chain structure to increase balancing speed. In this paper, balancing principle of conventional switched capacitor is explained and the mechanism of charge transfer between adjacent cell and faraway cell is analyzed. Two proposed circuits with the chain structure are described. From the chain structure, the uppermost cell can be adjacent cell of the undermost cell by using additional switches and capacitor, and it can achieve faster cell balancing. Balancing performances of the proposed circuits are confirmed with PSIM simulation, and comparisons between conventional and the proposed circuits are presented. Experimental results are also shown to verify the validity of the proposed structures.