Hysteresis Characteristics Analysis and SOC Estimation of Lithium Iron Phosphate Batteries Under Energy Storage Frequency Regulation Conditions and Automotive Dynamic Conditions

With the application of high-capacity lithium iron phosphate (LiFePO₄) batteries in electric vehicles and energy storage stations, it is essential to estimate battery real-time state for management in real operations. LiFePO₄ batteries demonstrate differences in open circuit voltage (OCV) under different charge and discharge paths, indicating the hysteresis phenomenon of OCV, which is more evident under energy storage frequency regulation conditions. Previous battery models ignored the hysteresis characteristics in the energy storage frequency regulation conditions, causing low accuracy in the state of charge (SOC) estimation. To accurately estimate the SOC of LiFePO₄ batteries, a hysteresis voltage reconstruction model is developed to analyze the hysteresis characteristics of LiFePO₄ batteries under automotive dynamic conditions and energy storage frequency regulation conditions. The accuracy of the hysteresis model is compared with the basic first-order RC equivalent circuit model. Furthermore, the SOC estimation based on the extended Kalman filter (EKF) method is achieved. Results indicate that the hysteresis model exhibits better accuracy for the hysteresis features, with an error of less than 1.5%, which is more appropriate for SOC estimation under energy storage conditions.