1. School of Mechanical Engineering, Hunan University of Technology, Zhuzhou， Hunan 412007, China; 2.Hunan Hongxunyian New Energy Technology Co.， Ltd., Zhuzhou， Hunan 412007, China
Abstract： To solve the problems of amperehour integration method for battery packs with inaccurate state of charge (SOC) estimation due to sensor accuracy, battery aging, integration error and initial value, the parameters of SOC initial value, nominal capacity and integration period of the traditional amperehour integration were improved. The firstorder RC equivalent circuit model was established based on the internal relationship between the SOC and the open circuit voltage (Uo). In the circuit model, the Uo was extracted and updated in real time by the recursive parameterfree least squares (PFRLS) with forgetting factor. The temperature with crucial effect on Uo was considered, and a threedimensional model of SOCUoθ was established to provide an accurate initial value for the improved amperetime integration method. Based on the inconsistency of battery pack, the maximum voltage and the minimum voltage fusion algorithm were proposed， and the federal urban driving schedule（FUDS) working condition detection and the real vehicle working condition verification were carried out. The results show that the accuracies of the PFRLS online extraction of Uo, the single cell SOC and the battery pack SOC algorithm are respective 2.55%, 3.20% and 4.00%, which meets the technical requirements of QC/T 897—2011 battery management system for electric vehicles claim.
