During the energy storage application,the large inconsistency of retired batteries lead to over-charging or over-discharging of the retired battery pack,which limits the overall capacity of the battery pack and even causes thermal runaway,causing safety hazards.To address these problems,an active e-qualization circuit was designed based on a bidirectional half-bridge LLC resonant converter.The equali-zation circuit can realize the energy transfer between the single cell and the battery pack through the inter-play of the switching array and the isolated bidirectional half-bridge LLC resonant converter,so that the energy balance of each single cell in the retired battery pack can be achieved.In addition,a multi-state equalization control strategy that combines voltage and state of charge(SOC)as equalization variables was proposed to further improve the equalization speed and accuracy of the equalizer.According to the differ-ent energy states of the battery pack,different equalization variables and corresponding equalization strat-egies were used in three different states of battery resting,charging and discharging to achieve fast equali-zation of the battery pack.Finally,the equalization experiments were carried out on six series-connected batteries by building a small equalization prototype.As the experimental results show,the proposed e-qualization method has faster equalization speed and better equalization effect.
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