A switchable indicator for active balance of the lithium-ion battery pack using a bypass equalizer

Balance techniques are critical for the Battery Management System (BMS) of a battery pack. If not well balanced, the performance of the battery pack will always be limited by the weakest cell. Battery State of Charge (SOC) is naturally an effective indicator for balancing, yet the SOC estimation cannot always be accurate, which may further induce uncertainties to the balance performance. Aiming to alleviate this issue, this paper proposes a switchable indicator for balancing a series-connected battery pack using a bypass equalizer with a compact topological structure, high efficiency and fault tolerance ability. The proposed switchable indicator enables automatically selecting the balance indicators between voltage and SOC, and a new balancing strategy is thus designed to utilize this switchable indicator. The proposed method is proven by both simulation and experiment on a lithium-ion battery pack.