Scientific Paper in IEEE Conference Proceedings
A New Non-recursive Analytical Calibration Approach for
Li-ion ECMs based on Voltage Gradient and Sigmoid Function
Jorge Varela Barreras1,2,3, Sergi Zapater Villar1,2, Ramon Guzman2, Damián González Figueroa1
1 Dept. Electric Vehicle Propulsion System and Validation, CTAG, Spain
2 Dept. Electronic Engineering, UPC, Spain
3 Dept. Civil & Environmental Eng., Imperial College London, UK
Abstract: Electrical Equivalent Circuit Models (EECMs) are commonly used for Li-ion battery simulation and state estimation due to their balance of accuracy and simplicity. However, their parameters change with operating conditions such as temperature, state-of-charge, and state-of-health, making traditional offline parameterization methods, based on static look-up tables, prone to inaccuracies. Existing online parameter estimation methods, including recursive least squares and Kalman filters, are computationally demanding and therefore often applied only at the pack level, neglecting cell-to-cell variations that worsen with ageing. Additionally, current methods struggle with the battery's mixed dynamics, introducing numerical challenges and higher memory requirements. Multi-timescale approaches offer solutions but still face significant complexity. In this paper, a new method is proposed to calibrate multi-order EECM based, for the first time in the literature, on non-recursive analysis of the terminal voltage gradient and key insights provided by the sigmoidal nature of the variable first order time constant. This simpler analytical approach requires minimal data, computational demand, and knowledge of prior battery characteristics. Exemplary simulation results based on synthetic data proof the robustness of the method, showing an error in cell voltage estimation <1% over a 90 s forecast period under CC discharge conditions. The method also provides key insights into the system’s dynamic behavior in relation to the order of the system and the calculation of its time constants, with an error <1%, from a relatively short time series data.
Where: 2024 Third International Conference on Sustainable Mobility Applications, Renewables and Technology (SMART)