A Novel Method for Estimating State-of-Charge of Lithium-ion Battery Pack Based on General Open Circuit Voltage

Abstract

The relationship between open-circuit-voltage (OCV) and the state of charge (SOC) has shown a considerable influence on the accuracy of SOC estimation. In this study, in order to deal with the uncertainty and inconsistency of the OCV curve in the battery pack, a novel method for SOC estimation based on the general OCV is proposed. The general OCV unifies the OCV curves of all the cells in the battery pack and can be used to solve the OCV derivative in EKF-based SOC estimation, but it brings model deviation meanwhile. Therefore, the battery model is corrected by the model bias, which is obtained by online identification with other model parameters. The case study results show that the results of SOC estimation is accurate and stable, with the maximum absolute error less than 6% at 0°C, 4% at 25°C and 45°C.