Battery Degradation and Performance
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Equivalent Circuit Model with Lithium Depletion (LD) Term for High-Power Discharge (eVTOL) Model Challenge The classical Equivalent Circuit Model (ECM) fails to reproduce sudden voltage decreases at low SOC (relevant for eVTOL applications). Proposed approach Additional diffusion resistance (RLD) in series to the RC elements is introduced (LD-ECM) in the equivalent circuit. The new term is parameterized through a set of of experimental aging data composed by constant current pulses (CCP), full discharge (FD) and multi power pulses (MPP). A LUT identification methodology with parameter regularization is introduced.
Main Results The model is validated against a data set of over 150 flights that cover wide conditions (from 30 oC to 60 oC and up to 8C of current rate) for eVTOL aircraft. Reserve time is suggested as the metric to track accuracy. A standard deviation of 6.2s over all tested duty cycles is achieved. However, maximum errors of up to 20s are observed.
Adding an additional diffusion resistance element in the Equivalent Circuit Model can capture battery behaviour at low SOC and improve model accuracy. However, lower temperatures (< 30°C) and battery degradation have yet to be addressed on their impact on model performance and accuracy. Source: A. Goshtasbi et al,, Journal of Power Sources 620 (2024) 235188
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