Fuzzy logic control-based charge/discharge equalization method for lithium-ion batteries

In this paper, a grouping equalization circuit based on the Single Ended Primary Inductor Converter (SEPIC) circuit is proposed, which can transfer energy between any single cell or grouped cells. Compared with the traditional equalization circuits that transfer energy between adjacent cells, the SEPIC circuit can directly connect any two batteries that need to be equalized; the number of circuit equalization paths is calculated based on a directed graph, then used as a basis for grouping the batteries to improve the equalization efficiency. In the charging or discharging condition, the amount of charge remaining in the battery to be charged or discharged is used as the control variable for equalization, and intra-group equalization is completed before inter-group equalization starts. To ensure the equalization efficiency of the battery, the equalization current is controlled by fuzzy logic control (FLC). Taking 10 single cells as an example based on the calculation of the number of equalization paths, two 5-cell groups can be confirmed as the optimal solution. Experiments were performed on Matlab/Simulink simulation platform, and the results show that compared with the traditional adjacent inductance equalization circuit, the equalization circuit proposed above reduces the time needed for equalization by 35.8%; Compared with the traditional average difference method, in charging and discharging conditions, the FLC algorithm saves times by 20.5% and 31.3% respectively, and energy loss is reduced by 9.1% and 5.5% respectively, which verifies the feasibility of the proposed equalization scheme.