Parameter sensitivity analysis and simplification of equivalent circuit model for the state of charge of lithium-ion batteries

Abstract

To ensure model accuracy, the model parameters in the equivalent circuit model (ECM) are updated frequently with varying state of health (SOH) and state of charge (SOC). In this work, the parameter sensitivity of the 2RC model with one-state hysteresis (2RCH) is investigated to determine the crucial parameters. Firstly, the model parameters of 2RCH is identified using particle swarm optimization under dynamic working conditions. Secondly, the sensitivity analysis of parameters in 2RCH for two types of batteries is qualitatively examined using the one-factor-at-a-time method. Thirdly, a simplified model, in which the crucial parameters with high sensitivities are updated with SOC and SOH, while the other parameters retain their initial values, is proposed to ensure model accuracy while reducing computational complexity greatly. Finally, SOC estimation based on the simplified ECM for two types of batteries over the whole SOC range under different SOHs is performed using the extended Kalman filter. The experimental results show that the SOC accuracy obtained by updating the crucial parameters is almost the same as that obtained by updating all parameters. The simplified model is beneficial to avoid unnecessary repeated calculation of model parameters for different SOC and SOH ranges in the SOC estimation.