Accurate State of Charge Estimation in Lithium-Ion Batteries by Second-Order Sliding Mode Observer

Abstract

Accurate state-of-charge (SoC) estimation in lithium-ion batteries is crucial for efficient energy management, safe operation, and extended battery lifespan. Although sliding mode observers (SMOs) are widely used for this purpose, conventional first-order designs often suffer from chattering and slow convergence, resulting in noisy and less reliable estimation signals. This paper proposes a finite-time second-order sliding mode observer (SO-SMO) for accurate SoC estimation based on an equivalent circuit model of the battery. The proposed observer analytically derives a closed-form expression for the finite convergence time, enabling predictable estimation dynamics. Moreover, it eliminates chattering and significantly improves estimation smoothness and robustness against modeling uncertainties and measurement noise. A comparative analysis with the Extended Kalman Filter and traditional SMO demonstrates that the proposed method achieves higher estimation accuracy and faster convergence while maintaining lower computational complexity, making it well-suited for real-time applications. Theoretical analysis and simulation results confirm that the SO-SMO offers a superior balance between accuracy, robustness, and efficiency, establishing its potential for next-generation battery management systems in electric and hybrid vehicles.

Keywords

chattering / lithium-ion battery / sliding mode observer / state of charge

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2026 The Author(s). Battery Energy published by Xijing University and John Wiley & Sons Australia, Ltd.