Considering the limitations in existing voltage-based and state-of-charge (SOC)-based active equalization strategies, including the difficulty in threshold value determination for equalization system on/off controlling, repeated estimation for equalization variable and the corresponding tremendous complexity, this paper designs a novel residual cap. ••A novel residual capacity-based active equalization strategy is designed.••A data-driven residual charging capacity estimation method is developed.••The optimal combination of in-pack cells' equalization current is searched by PSO.••The maximum voltage difference among all in-pack cells can be limited below 0.01V.••Cells'. Lithium-ion battery packActive equalization strategyData-driven residual charging capacity estimationEqualization current calculation1.1. The motivations of this workIn the text of global warming and shortage of fossil fuels, electric vehicles (EVs) have been seen as a promising alternative for conventional vehicles and become extremely popular in the recent years (Chen et al., 2022; Abu et al., 2023; Han et al., 2023). Considering the limited voltage and capacity of one single lithium-ion battery cell, hundreds to thousands of cells are usually connected in series or parallel as the power unit to provide sufficient power for EVs. In this case, inconsistencies in cells caused by the inconsistent manufacturing process and the inhomogeneous operating conditions will inevitably accelerate the degradation of in-pack cells and lower the performance of the whole battery pack (Kallitsis et al., 2022; Rojas and Khan, 2022). To mitigate the aforementioned issues due to cell-to-cell variations, a reliable and effective equalization strategy is required in battery management system (BMS).1.2. Literature reviewCurrent equalization strategies can be classified as two groups: passive equalization strategies and active equalization strategies. In passive equalizati. In this work, the Oxford battery degradation dataset is used to illustrate and further verify the developed active equalization strategy. In this dataset, eight Kokam pouch batteries with the nominal capacity of 740mAh were tested under 40 °C. As summarized in Table 1, the degradation experiment has two parts: characterization tests and drive cycles.Table 1. Testing procedures of the Oxford battery degradation dataset.
