SOC estimation of lithium-ion battery considering the influence of discharge rate

When the battery is used under the condition of the intermittent pulse discharge with gradually decreasing amplitude, its parameters change largely and it is not easy to predict its state of charge (SOC) with precision. As a solution, a second-order RC equivalent circuit model of Li-ion battery with consideration of the influence of discharge rate is developed. Firstly, to identify related parameter of battery model through the battery test data at different rates. Critical parameters are configured as the function related to the current. Secondly, to develop the state equation and the observed equation of the battery over the improved parameter model. Finally, to exercise the extended Kalman filter (EKF) algorithm for the estimations of battery's SOC. Experiments indicate that, under the condition of the intermittent pulse discharge with gradually decreasing amplitude, compared with the case without considering the effect of discharge rate, by applying the improved battery model, the deviation in the process of SOC estimation can be effectively corrected and the precision for estimating SOC can be significantly ameliorated.