| Summary: | The state of charge (<i>SOC</i>) of the battery is an important basis for the battery management system to perform state monitoring and control decisions. In this paper, by identifying the internal parameters of the battery model at different temperatures and <i>SOC</i>s of the lithium-ion battery, the specific factors that affect the change of the parameters are analyzed, the segmentation basis of the model and the fitting method of related parameters are discussed, the second-order equivalent circuit model of the lithium-ion battery whose parameters vary with <i>SOC</i> and temperature is established, the unscented Kalman filter (UKF) is used to estimate the <i>SOC</i> of the lithium-ion battery, and an improved <i>SOC</i> estimation method based on optimized equivalent circuit model is proposed. Simulation and experimental results show that the improved <i>SOC</i> estimation strategy can obtain high estimation accuracy in a wide temperature range.
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