State‐of‐charge estimation of the lithium‐ion battery system with time‐varying parameter for hybrid electric vehicles

This study addresses the state‐of‐charge (SOC) estimation problem for a lithium‐ion battery system with time‐varying parameter. Although many methods have been proposed for the SOC estimation, the time‐varying parameter problem has not been solved perfectly up to now. In this study, by introducing a novel physical meaning for that the battery terminal current is ℒ 2 ‐norm bounded and solving one linear matrix inequality, a robust H ∞ filter is proposed for the first time to estimate the SOC of the lithium‐ion battery of hybrid electric vehicles. The proposed method is evaluated by the sequence of urban dynamometer driving schedule test. The experimental results show that the filter proposed here is more accurate and reliable than that without considering the time‐varying parameter.