State of Charge Estimation for Electric Vehicle Battery Using Fuzzy Sliding Mode Observer

In recent years, the development and utilization of Lithium-ion batteries have further promoted the development of electric vehicle and related battery management systems. Estimating the battery state of charge (SoC) is essential for battery management systems. Most studies on SoC estimation have focused on model-based observer designing. The sliding mode control strategy is suitable for estimating the battery SoC due to its strong robustness, insensitivity to parameter perturbation and external disturbance, and high estimation accuracy. This paper aims to design a battery SoC estimator using the proposed fuzzy sliding mode control strategy. The fuzzy control logic is introduced to suppress chattering by regulating the switching gain in the sliding mode control law. Firstly, the second-order Thevenin equivalent circuit model of the battery is established. Then a fuzzy sliding mode observer is designed based on the equivalent circuit model to estimate the battery’s SoC. Finally, the designed observer is simulated and verified.