Cell equalization is an effective approach to mitigating inconsistency issues in lithium-ion battery packs, and accelerating equalization speed through advanced technologies is a major focus of current research. This paper proposes a dual-layer equalization topology for series-connected lithium-ion battery packs. The lower-layer adopts a bidirectional Cuk converter topology, where each equalization unit consists of two adjacent cells to enable energy transfer between neighboring cells. The upper-layer employs a flyback converter structure, in which a switch array is used to realize energy transfer between any individual cell unit and the entire battery pack. Furthermore, a cascaded cooperative equalization strategy based on Model Predictive Control and dual-loop Proportional-Integral (MPC-PI) control is developed. Utilizing the battery State of Charge (SOC) as the state variable, the MPC algorithm establishes a discrete-time predictive model and solves a composite optimization objective function to generate the optimal switching sequence. Concurrently, the dual-loop PI controller regulates the forward and reverse operating states of the circuit, executing precise energy transfer to achieve dynamic equalization among individual cells. Finally, experimental validation was conducted using an 8-cell lithium-ion battery packs on the MATLAB/Simulink simulation platform. Simulation results across static, charging, and discharging conditions indicate that the proposed Cuk-flyback topology reduces equalization time by 48.84%, 43.35% and 55.45%, respectively, compared with the conventional single-layer Cuk topology. Meanwhile, the MPC-PI control strategy improves equalization speed by 33.07%, 32.64% and 33.91% compared to the conventional MPC approach. Consistency analysis results indicate that the proposed equalization scheme can effectively improve the equalization speed while maintaining high consistency, with the final SOC standard deviation (SD) reduced to below 0.7%.
Wu et al. (Thu,) studied this question.