Equivalent hysteresis model based SOC estimation with variable parameters considering temperature

Estimation of the state of charge (SOC) of a lithium-ion battery is one of the key technologies in battery management systems. The accuracy of SOC estimation mainly depends on the accuracy of the battery model. The traditional Thevenin model has limited application due to its fixed parameters. In addition, its accuracy is not high. This paper proposes a variable parameter equivalent hysteresis model based on the Thevenin model. The parameters of this model are regarded as variables that vary with temperature and SOC. They can be identified by hybrid pulse power characteristic (HPPC) experiments. In addition, the model also considers the hysteresis characteristics of the open circuit voltage (OCV) and uses a mathematical recursive equation to describe it. Experimental and simulation results show that the proposed model has a higher accuracy and a wider application than the Thevenin model. On the basis of this model, SOC estimation is carried out based on modified covariance extended Kalman filter (MVEKF) at different temperatures. The results show that the SOC estimation accuracy of the MVEKF method is significantly higher than that of an extended Kalman filter (EKF).