A new estimation method of Li-batteries SOC based on composite EKF

State of charge(SOC) of power battery pack is an important parameter for electric vehicle. The extended Kalman filter and the current integral method were applied to estimate SOC of Li-ion battery pack with multi cells in series. Thevenin model was built with extended Kalman filter, and the minimal voltage of the battery pack was regarded as its voltage. By applying the composite extended Kalman filter, dynamaic state estimation of SOC was realized. The experiment was made to simulate the behaviors of battery pack in the actual work condition of electrical vehicle. The result shows that the composite EKF is more accurate than EKF and meet the need of real-time estimation of SOC.