Research on layered equalization control of decommissioned lithium battery packs based on DC/DC converter

In order to solve the battery life degradation problem caused by the inconsistency of retired lithium battery groups and to improve the equalization efficiency, a two-layer topology with an improved buck-boost circuit in the inner layer and a bidirectional flyback transformer equalization topology in the outer layer is proposed. The improved buck-boost circuit is used for equalization within the group, and the buck-boost converter is connected to the equalization battery through a selector switch, and soft-switching technology is introduced to realize the zero-voltage conduction of the switching tubes and reduce the switching loss. Bidirectional flyback transformer equalization is used between groups to achieve energy equalization between any battery groups. The layered equalization circuit takes SOC as the equalization variable, and uses fuzzy logic control to optimally control the duty cycle and dynamically adjust the size of the equalization current during the equalization process, so that the series-connected battery packs can be quickly equalized under the premise of ensuring the safety of the batteries. An equalization simulation model is constructed in MATLAB/Simulink, and the experimental results show that the proposed hierarchical equalization topology circuit and fuzzy logic control strategy have good equalization speed and equalization effect under the charging and discharging state of the battery pack.