Fractional Order Terminal Sliding Mode Observer for State of Charge Estimation of Lithium-Ion Battery

Lithium-ion battery is widely used for its high energy density, long cycle life, non-pollution and other advantages. They are expected to be mainstream power source for future applications on electrochemical energy storage. However, it has been a long-standing problem to obtain an accurate real-time state estimation for lithium-ion battery with high nonlinearity and inevitable inconsistency. In this paper, the design of a new estimation method for state of charge (SOC) of lithium-ion battery is introduced. Based on the equivalent Thevenin model, a fractional order sliding mode observer is proposed to estimate terminal voltage, SOC and polarization voltage and the stability proof is given. Compared to the frequently-used Kalman filter method and the current integration method, this method shows higher accuracy and robustness. As a result, the feasibility of the proposed method is verified.