A Method for Estimating the State of Charge and Identifying the Type of a Lithium-Ion Cell Based on the Transfer Function of the Cell

Scientific paper - Original scientific paper

• Author: Ivan Radaš
• Author: Luka Matić
• Author: Viktor Šunde
• Author: Željko Ban
• Author's institution: University of Zagreb; Faculty of Electrical Engineering and Computing
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Electrical Engineering

Abstract (english)

This paper proposes a new method for assessing the state of charge (SoC) and identifying the types of different lithium-ion cells used in battery systems of light electric vehicles. A particular challenge in the development of this method was the SoC estimation time, as the method is intended for implementation in the control system of a bicycle charging station, where the state of charge must be determined immediately after the bicycle is plugged in to start the charging process as quickly as possible according to the appropriate charging algorithm. The method is based on the identification of the transfer function, i.e., the dynamic response of the battery voltage to the current pulse. In the learning phase of this method, a database of reference transfer functions and corresponding SoCs for every specific type of battery cell is created. The transfer functions are described by coefficients determined through the optimization procedure. The algorithm for estimating the unknown battery cell SoCs is based on the comparison of the measured voltage response with the responses of the reference transfer functions from the database created during the learning process to the same current signal. The comparison is made by calculating the integral of the square error (ISE) between the response of the specific reference transfer function and the measured voltage response of the battery cell. Each transfer function corresponds to a specific SoC and cell type. The specific SoC of the unknown battery is determined by quadratic interpolation of the SoC near the reference point with the smallest ISE for each battery type. The cell type detection algorithm is based on the fact that the integral squared error criterion near the actual SoC for the actual cell type changes less than the ISE criterion for any other battery cell type with the same SoC. An algorithm for estimating the SoC and cell type is described and tested on several different cell types. The relative error between the estimated SoC and the actual SoC was used as a measure of the accuracy of the algorithm, where the actual SoC was calculated using the Coulomb counting method.

• Keywords (english): lithium-ion battery; battery cell’s state of charge; SoC estimation; battery cell’s transfer function; battery cell type estimation
• Language: english
• Publication type: Scientific paper - Original scientific paper
• Publication status: Published
• Peer review: Peer review - international
• Publication version: Published version
• Journal title: Processes
• Numbering: vol. 12, no. 404, pp. 1-17
• e-ISSN: 2227-9717
• DOI: https://doi.org/10.3390/pr12020404
• URN:NBN: urn:nbn:hr:168:559847
• Publication: 2024-02-17
• Project: Number: KK.01.1.1.07.0066; Title (croatian): Razvoj napredne punionice električnih bicikala za pametni grad; Title (english): Development of an advanced electric bicycle charging station for a smart city; Acronym: PUELBI; Jurisdiction: eu; Funding stream: European Regional Development Fund
• Document URL: https://www.mdpi.com/2227-9717/12/2/404
• Type of resource: Text
• Access conditions: Open access
• Created on: 2024-07-10 13:32:38