Cell imbalance is one of the key factors that limit the capacity and power of battery energy storage systems (BESS), especially the large lithium-ion battery packs. To deal with the unbalancing problem, an effective balancing circuit is required, so is an optimal balancing strategy. In this paper, an optimal strategy for cells balancing has been presented. Contrary to the conventional balancing algorithms which base on instantaneous voltage or state-of-charge (SOC) no matter what the cause of

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... balance is, the proposed strategy is targeted to different imbalance situations. Four cases of cell imbalance have been analyzed and the balancing effects of different algorithms are discussed. The simulation results show that the proposed strategy improves the performances of battery packs, including the usable capacity and maximum power.