Research on two-stage equalization strategy based on fuzzy logic control for lithium-ion battery packs

In this paper, a two-stage equilibrium topology based on the Buck-Boost circuit is proposed to solve the problem of inconsistency of series lithium-ion battery packs. The equalization topology is divided into two forms: intragroup and inter-group, the centralized equalization topology based on single inductor is adopted within the battery pack, which can equalize any single cell within the group, and the equalization circuit within each pack can equalized simultaneously, while the Buck-Boost circuit topology is used between the battery groups, which can equalize adjacent packs. The state of charge (SOC) of the battery is taken as the equilibrium variable, and the fuzzy logic control (FLC) algorithm is designed to dynamically adjust the equalization current to reduce equalization time and improve equalization efficiency. Matlab/Simulink software is used to build the model and simulate it. The experimental results demonstrate that the proposed topology saves approximately 23.70% of the equalization time compared to the traditional single inductor centralized bi-directional active equalization topology. Under the same static and charge/discharge conditions, the equalization time is reduced by about 22% after equalization using the FLC algorithm compared to the maximum value equalization method. The feasibility of the equalization scheme is verified.