Manufacturing dispersion and non-uniform aging can lead to state-of-charge (SOC) imbalance in series-connected lithium-ion cells, resulting in reduced usable capacity and accelerated degradation. In this work, a hierarchical balancing scheme for lithium-ion battery packs is investigated. Cell-level balancing within battery modules is realized using an inductor-based topology, while energy transfer between modules is achieved through a dual-capacitor boost circuit. The balancing sequence and energy transfer direction are determined according to SOC comparison, with the SOC difference serving as the termination condition. The operating principles of the circuit and the corresponding control method are presented and analyzed. Simulation and experimental studies are carried out on a four-cell battery pack with different initial SOCs. The results show that, under the studied operating condition, the proposed scheme completes SOC equalization in about 2860 s in simulation and about 2950 s in experiment, thereby demonstrating the effectiveness of the hierarchical balancing circuit and its corresponding control method.
Wang et al. (Thu,) studied this question.