Combined RLS-?KF Method for Simultaneous SOC and Parameter Estimations for Lithium-Ion Batteries

This paper is concerned with the State-Of-Charge (SOC) estimation for lithium-ion batteries based an equivalent circuit model. A method for simultaneous estimation of the SOC and circuit parameters is presented by combining the extended Kalman filter (EKF) and the recursive least squares (RLS) estimation methods. The estimation accuracy of the present method is assessed through a discharge experiment of a LiFePO4 battery. In particular, the AC impedance analysis using the Cole-Cole plots shows that the parameter estimates obtained by the RLS part well describe the behavior of the battery in the operating frequency range. This supports the effectiveness of the present method.