A novel state-of-charge estimation method for lithium-ion battery pack of electric vehicles

In this paper, a novel state-of-charge (SOC) estimation method is proposed for lithium-ion battery packs of electric vehicles. An equivalent circuit model, which comprises an open circuit voltage source and a resistance-capacitance network connected in series, is built for each cell to characterize its dynamic and static performance. Then, the EKF is applied to calculate each cell's SOC. By calculating and screening all the cells' SOC, a group of parameters, which include a weighed SOC value, SOC variance value, maximum and minimum cell SOC, are selected to represent the pack SOC. Experiment results prove that the proposed method can calculate the pack SOC more reasonably, thus ensuring safer operation of the battery pack.