SOC Estimation for Li-Ion Batteries Based on Equivalent Circuit Diagrams and the Application of a Kalman Filter

Batteries play an essential role in electric vehicles (EV), and obtain more and more importance also in smart grids due to the non-constant power generation of renewable energy sources. In order to achieve an optimum operation of systems with batteries it is necessary to develop accurate mathematical models for the calculation of the state of charge (SOC), taking into account the individual operation by the user. This paper presents the fundamentals of a method how to determine SOC of lithium-ion batteries on the basis of two different equivalent circuit diagrams and an Extended Kalman Filter (EKF). The comparison between measurement and computation results shows a good accordance. The accurate determination of SOC of a battery in an EV is of high importance for the prediction of the distance that can be driven. In the first step the dependency of these parameters on the temperature and on the battery age is neglected.