Capacity and state‐of‐charge (SOC) estimation for lithium‐ion cells based on charging time differences curves. (10th August 2022)

• Record Type: Journal Article
• Authors: Zheng, Yuejiu; Pang, Kang; Xu, Chaojie; Su, Teng; Rohit, Bhagat; Guo, Yue; Han, Xuebing
• Is Part Of: International journal of energy research. Volume 46:Number 13(2022)
• Page Start: 18757
• Page End: 18767
• Publication Date: 2022-08-10
• Subjects: capacity estimation -- charging curves -- charging time difference curve -- Lithium‐ion batteries -- SOC estimation; Power resources -- Periodicals; Power (Mechanics) -- Periodicals; Power resources -- Research -- Periodicals; 621.042
• DOI: 10.1002/er.8495
• Languages: English
• ISSNs: 0363-907X

Abstract

Summary: The battery pack of electric vehicles (EV) is generally composed of multiple cells in series. Due to the inconsistency between the cells in the production process and use stage, the capacity and state‐of‐charge (SOC) of the cells will be different. We propose an online estimation method based on the charging curve similarity principle in this paper. The proposed method uses a series of charging time differences (CTD) during the charge. By analyzing the CTD curve, the capacity and SOC difference can be achieved. The first‐order resistance circuit model is used for the series charging curve simulation. Further experimental verification is conducted using two groups of four cells in series. In simulations and experiments, the error of the proposed capacity estimation method and the initial SOC error are less than 1%. Finally, the robustness of the proposed method is verified using EV cloud data. The results demonstrate that the proposed method has good robustness at the level of EV cloud data. Abstract : In this study, based on the principle of the similarity of charging curves, this paper proposes an online estimation method for the cell capacity and initial SOC in the battery pack. Through the transformation of charging curves, the corresponding relationship between the slope (and/or intercept) of the CTD curve and the capacity (and/or initial SOC) of the cells in the battery pack are established. The capacity and initial SOC of other series cells in the battery pack are calculated.