Abstract: To accurately estimate the state of charge (SOC) of lithium battery,the Thevenin equivalent circuit model was selected,the OCV-SOC curve was fitted by piecewise linearization,and the SOC estimation method based on extended Kalman filter (EKF) and capacity calibration was adopted.The state space equation of the battery was established.Considering the aging factors of the battery,the total capacity was calibrated by the method of combining SOC estimation and ampere-hour integration.The simulation and experimental verification were carried out under the federal urban driving sechedule operating condition.The results show that the SOC estimation error of the proposed scheme is within 2.1%.

Key words: state of charge (SOC), lithium batteries, Thevenin equivalent circuit model, extended Kalman filter (EKF), capacity calibration