High-Efficiency Active Equalization for Li-ion Battery Packs

To address inconsistencies among individual cells in series-connected lithium-ion battery packs, this paper proposes a high-efficiency active equalization system based on the state-of-charge (SOC) estimation, and an improved inductive-capacitive balancing topology. An Extended Kalman Filter (EKF) algorithm is employed to estimate the battery SOC using a second-order RC equivalent circuit model with identified parameters. Simulation results under New European Driving Cycle (NEDC) conditions demonstrate that the proposed EKF method significantly improves SOC estimation accuracy, with an estimation error maintained within 0.5%, providing a reliable basis for balancing control. To improve equalization efficiency and reduce switching losses, the conventional hierarchical single-inductor layered topology is enhanced by introducing switching devices and reducing the number of diodes. Furthermore, a multi-mode equalization control strategy with three operating modes is developed to enable flexible balancing under different operating conditions. Simulation models of both the conventional hierarchical topology and the proposed improved topology were implemented in the Matlab/Simulink environment for comparative analysis. The results indicate that the proposed topology significantly improves equalization performance, achieving reductions in balancing time of 16.7%, 3.9%, and 14.1% under static, discharging, and charging conditions, respectively. These results demonstrate that the proposed equalization system provides improved balancing efficiency and reduced energy loss, offering a promising solution for lithium-ion battery management systems.