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Automotive Engineering ›› 2021, Vol. 43 ›› Issue (1): 19-26.doi: 10.19562/j.chinasae.qcgc.2021.01.003

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An Overall Estimation of State⁃of⁃Charge Based on SOC⁃OCV Optimization Curve and EKF for Lithium⁃ion Battery

Xin Lai(),Yunfei Li,Yuejiu Zheng,Jingjing Wang,Tao Zhou Long Sun   

  1. College of Mechanical Engineering,University of Shanghai for Science and Technology,Shanghai 200093
  • Received:2020-04-22 Revised:2020-07-24 Online:2021-01-25 Published:2021-02-03
  • Contact: Xin Lai E-mail:laixin@usst.edu.cn

Abstract:

The SOC?OCV curve is the basis of the state estimation for lithium?ion battery. To solve the problems of failure of the traditional HPPC test method to describe the nonlinear characteristics of the battery at non?test points and the low accuracy of the OCV curve by the small?constant?current discharge method, an OCV curve optimization method based on the particle swarm optimization algorithm is proposed. In this method, the OCV curve by the small?constant?current discharge method is translated, and the OCV curve is optimized by minimizing the sum of error between the translation curve at the test point and the OCV value obtained by HPPC test. Then, the model parameters of the second?order RC model are identified and the model terminal voltage is estimated based on the optimized OCV curve. The experimental results show that the overall model accuracy based on the optimized OCV curve is higher than that based on HPPC, and the former is twice the accuracy of the latter in the low SOC region. Finally, based on the optimized OCV curve and identified model parameters, an EKF algorithm is designed to estimate the SOC in the whole SOC region. The test results show that the SOC estimation error based on the optimized OCV curve and EKF algorithm can keep within 2% over the whole SOC region.

Key words: lithium?ion battery, second?order RC model, SOC?OCV curve optimization, SOC estimation, extended Kalman filter