Improved sliding mode observer-based SOC estimation for lithium battery

In this paper, lithium battery state of charge (SOC) is estimated by using sliding mode observer and H∞ filter. Firstly, through the discharge experiment, parameters of the second-order RC equivalent circuit model of battery are identified. Secondly, by combining sliding mode observer method and H∞ filtering algorithm, the SOC estimation error covariance matrix in real time is updated for adjusting the observation gain matrix. An improved sliding mode observer is designed to estimate the battery’s SOC. Simulation results show that the designed control algorithm has higher estimation accuracy, and the estimation error is lower than 5%, which is 2% higher than H∞ filtering algorithm and 7% higher than that of sliding mode observer.