A Review of Sliding Mode Observers Based on Equivalent Circuit Model for Battery SoC Estimation

Battery technology is a major technical bottleneck with electric vehicles (EVs). It is necessary to perform state of charge (SoC) estimation in order to ensure battery safe usage and reduce its average lifecycle cost. Sliding mode observer (SMO) has been used widely in battery SoC estimation owing to its simplicity and robustness to both parameter variations and external disturbances. The SMO uses a switching function of the model error as feedback to drive estimated states to a hypersurface where there is no difference between measured and estimated output exactly. In this paper, three kinds of SMOs based on equivalent circuit model (ECM) for SoC estimation in the existing literatures are reviewed. Their difference in the structures and principles are discussed in the hope of providing some inspirations to the design of efficient SMO based SoC estimation methods.