State-of-charge estimation and uncertainty for lithium-ion battery strings

• Published in: Applied energy Vol. 119; pp. 218 - 227
• Main Authors: Truchot, Cyril, Dubarry, Matthieu, Liaw, Bor Yann
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.04.2014; Elsevier
• Subjects: Applied sciences; Battery; Battery strings; BMS; Cell variability; Conventions; Direct energy conversion and energy accumulation; electric power; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Energy; Exact sciences and technology; lithium batteries; Lithium-ion batteries; Management; Open circuit voltage; Product safety; State function; State-of-charge (SOC) estimation; Strings; thermodynamics; Uncertainty; State function; BMS; Uncertainty; Battery strings; State-of-charge (SOC) estimation; Cell variability; Variability; Battery; Lithium
• DOI: 10.1016/j.apenergy.2013.12.046
• ISSN: 0306-2619

•A new state-of-charge (SOC) convention to accurately represent the state of the battery.•The best SOC estimation method is proposed and validated for a string of batteries.•Basic understanding of SOC from materials in electrodes to multi-cell strings is explained.•Error functions from five SOC estimation methods are evaluated and compared.•Uncertainty on SOC estimation was estimated, discussed and explained. The state-of-charge (SOC) estimation is of extreme importance for the reliability and safety of battery operation. How to estimate SOC and, to some degree, the SOC convention itself, is still a subject of great interest. Here a viable SOC convention valid for single cells and multi-cell strings is proposed and validated. Using a 3S1P string as an illustration in this work, the direct inference from a correct open circuit voltage versus SOC (OCV=f(SOC)) correspondence based on the proposed SOC convention is the best method for accurate SOC estimation among several possible approaches for strings. The thermodynamic aspect on this SOC convention is explained. Uncertainties in actual applications are also discussed. The understanding on this accurate SOC estimation approach shall facilitate reliable battery control and management.