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Research unit
SFOE
Project number
SI/502441
Project title
HYSTIMATOR – Automated online hysteresis estimation for improved state estimation for LFP batteries

Texts for this project
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Short description
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Publications / Results
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Final report
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Short description
(German)

Im Projekt HYSTIMATOR wird die Schätzung des Ladezustands (SoC) von LFP-Zellchemien verbessert. Die SoC-Schätzung ist aufgrund einer flachen Entladekurve und eines bedeutenden Hystereseeffekts schwierig. Der BESTIMATOR™-Algorithmus, ein erweiterter Kalman-Filter auf der Grundlage von Zustandsinformationen, die durch Online-Elektroimpedanzspektroskopie (EIS) gewonnen werden, wird so angepasst, dass er Hystereseeigenschaften einbezieht, die automatisch auf der Basis von EIS-Daten geschätzt werden.
Short description
(English)

The HYSTIMATOR project targets to improve state-of-charge (SoC) estimation for LFP cell chemistries. SoC estimation for LFP batteries is difficult due to a flat discharge curve and an important hysteresis effect. The BESTIMATOR™ algorithm, which is an extended Kalman filter based on state information extracted via online electro-impedance spectroscopy (EIS), will be adapted to incorporate hysteresis characteristics, which are scheduled to be estimated automatically based on EIS data.
Short description
(French)

Le projet HYSTIMATOR a pour objectif d'améliorer l'estimation de l'état de charge (SoC) des batteries LFP. L'estimation du SoC pour les batteries LFP est difficile en raison d'une courbe de décharge plate et d'un important effet d'hystérésis. L'algorithme BESTIMATOR™, qui est un filtre de Kalman étendu basé sur les informations d'état extraites via la spectroscopie d'électro-impédance (SIE) en ligne, sera adapté pour intégrer les caractéristiques d'hystérésis, dont l'estimation automatique est prévue sur la base des données SIE.
Publications / Results
(English)
Guillaume Thenaisie, Claudio Brivio: "Hystimator: DRT-based hysteresis modelling for accurate SoC estimation in LFP battery cells", IET Renewable Power GenerationVolume 18, Issue S1 pp. 4387-4398 (2024)
https://doi.org/10.1049/rpg2.13130
Final report
(English)
Based on recent advances in non-equilibrium thermodynamics, a new approach to the modelling of the hysteresis of LiFePO4 is proposed. A method for characterizing the hysteresis based on electrochemical impedance spectroscopy (EIS) is presented, which allows to reduce the characterization time from multiples weeks to few days. The results show that hysteresis in LiFePO4 is a very slow relaxation process strongly correlated with prior works results in crystalline phase transitions. An Electrical Circuit Model (ECM) of the cell is then extracted by using the distribution of relaxation times (DRT) on the EIS profile of the cell. The extracted DRT parameters show good agreement at low frequencies with previous thermodynamic studies. The performance of the ECM is compared with state of art physics-based ECM (without hysteresis compensation) for both fresh and aged cells. The result show an RMSE reduction of two to four folds depending on the tested cycling profile.
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