SOC estimation for a lithium-ion battery by designing a nonlinear observer based on an equivalent circuit model

In this paper, a nonlinear observer is proposed for estimation of the State of Charge (SOC) of a Lithium-Ion battery based on an equivalent circuit model, which consist one parallel RC network. Compared with other nonlinear observers, in the proposed method the nonlinear part of the model contributes directly in determination of the observer gain, allowing the observer to better compensate for the estimation error. The asymptotic stability of the observer is proved using the Lyapunov criteria. The effectiveness of the proposed observers is verified by using simulation in MATLAB software. The simulation results show that the proposed method is effective and estimates the SOC with high accuracy.