A Robust Estimation of State of Charge for Electric Vehicle Batteries

Knowledge of state of charge (SOC) is extremely important for electric vehicle batteries. This paper proposes a sliding mode observer for reliable and real-time estimation of the SOC. Nonlinear dynamics of the battery is considered, and parametric and modelling uncertainties are modelled as additive disturbances. Robustness performance of the proposed observer is guaranteed using input-to-state stability (ISS) theory. This indicates that the proposed observer is robust against parametric and modelling uncertainties, and can guarantees an upper bounded estimation errors. A designed method of the observer gains is presented following the stability analysis result. The proposed observer is implemented in an embedded hardware based on Freescale MPC5554, and is validated using datasets from a lithium-ion battery under different temperatures. The robustness of the observer against model parameter uncertainties, sensors biases, and measurement noises, which may appear in real vehicles, is evaluated. The experimental and robustness testing results confirm that the proposed observer achieves good performance on estimation accuracy, real time, and robustness.