Design and Study on the State of Charge Estimation for Lithium-ion Battery Pack in Electric Vehicle

State of charge (SOC) estimation is an increasingly important issue in battery management system (BMS) and has become a core factor to promote the development of electric vehicle (EV). In addition to offering the real time display of battery parameters to user, the accurate SOC information would exert some controls over the charging and discharging process that in turn reduces the risk of cell over voltage. Considering the shortcoming of traditional estimation methods and the harsh requirements in EV environment, a new method named combination algorithm is proposed in this paper in accordance with the characteristics of lithium-ion power battery. Some capacity effect factors, such as current rate and cell temperature, are also taken into consideration in the algorithm. The dynamic discharge test shows that the maximal SOC estimation error is less than 5%, which validates the feasibility and availability of the combination algorithm in the SOC estimation of electric vehicle.