Simply designed and universal sliding mode observer for the SOC estimation of lithium-ion batteries

A new sliding mode observer to estimate the state of charge (SOC) of lithium-ion batteries is presented. The proposed observer has been developed from a previous observer. The observer is applicable to the common battery circuit models and the design of the algorithm is simple. The observer can also be used for state estimations of both time-varying and time-invariant systems. The robustness of the observer is proved by Lyapunov stability theory. In this study, two typical circuit models are used as examples to design the observer and this study shows that the design of the observer is simple and the observer exhibits good performance. The observer is used to estimate the battery SOC under two conditions. The estimation results show that the observer is robust and the adaptive method can improve the estimation accuracy.