Non-Dissipative Equalization Method with SOC-Difference Based on Fuzzy Logic Control for Lithium-Ion Battery

A non-dissipative equalization method is proposed to reduce the inconsistency of series-connected Lithium-ion batteries. The proposed battery equalization method mainly consists of three parts: equalization circuits, equalization variable estimation, and equalization control strategy. Specifically, a bidirectional equalization circuit based on capacitance as energy transferring media is designed to implement the equalization of cell to cell for battery packs, which enables equalization between different cells in the same battery module or different battery module. Subsequently, state of charge (SOC) is selected as the equalization variable, and a sliding mode control (SMC) observer is designed for SOC estimation. Finally, in order to realize effective equalization process of the proposed equalization circuit scheme, an equalization control strategy based on fuzzy logic control (FLC) is designed. The experimental results show that the balancing time of the proposed control strategy is reduced by 6.87% compared with the mean-difference algorithm under both the steady state and the NEDC working condition. Besides, the proposed equalization strategy considers the DC/DC temperature, which avoids DC/DC heat damage and improves the security of the proposed equalization scheme. Therefore, the proposed non-dissipative equalization method has good performance and makes an important contribution to reduce the battery inconsistencies.