Equalization of Lithium-Ion Battery Pack Based on Fuzzy Logic Control in Electric Vehicle

A nondissipative equalization scheme based on fuzzy logic control (FLC) is presented to improve the inconsistency of series-connected Lithium-ion batteries. The two-stage bidirectional equalization circuit with energy transferring inductors is designed to implement the equalization of cell to cell for battery packs, and the equalization circuit paves the way for module-based equalization of hardware. Equalization based on the state of charge (SOC) is proposed in this paper, and the Thevenin equivalent circuit model of the Lithium-ion battery, as well as the extended Kalman filter (EKF) algorithm, is employed for SOC estimation. For effective equalization, the FLC is proposed to reduce energy consumption and equalization time. The FLC strategy is constructed with a set of membership functions to describe the equalization behavior of the cell. A comparison of the proposed FLC with the mean-difference algorithm is carried out to validate the advantages of the proposed scheme. Simulation results show that the standard deviation of final SOC reduces by <inline-formula><tex-math notation="LaTeX">${\text{18}}{\text{.5}}\%$</tex-math></inline-formula> , and equalization time decreases by <inline-formula><tex-math notation="LaTeX">${\text{23}}\%$</tex-math> </inline-formula> for FLC compared with the mean-difference algorithm under new European driving cycle working conditions. The energy efficiency improves by <inline-formula><tex-math notation="LaTeX">${\text{5}}{\text{.54}}\%$ </tex-math></inline-formula> compared with the mean-difference algorithm. In addition, the two-stage bidirectional equalization circuit has good performance and improves the inconsistency.