Christophe Forgez

Impedance Observer for a Li-Ion Battery Using Kalman Filter

Most methods for state-of-charge or state-of-health prognostics are impedance based. Impedance models must be as simple as possible to be implemented on embedded applications but as accurate as possible to represent the main electrochemical phenomena. The parameters of such models can be identified using impedance spectroscopy. However, the electrochemical features change in relation to numerous parameters, such as temperature or aging, which involves updating the model of the battery online. This paper deals with the use of an extended Kalman filter (EKF) for the observation of the parameters of a Li-ion battery lumped model. First, this paper will focus on the electrical model that can be used to represent the main electrochemical phenomena in the battery. Then, mathematical considerations about the EKF are reminded to be applied to the observation of the impedance parameters of the battery. This method has been validated on an urban driving cycle of a hybrid electric vehicle.

Study of graphite/NCA Li-ion cell degradation during accelerated aging tests — Data analysis of the SIMSTOCK project

This paper presents a preliminary analysis of aging data from the French SIMSTOCK program in order to evaluate the influence of several aging factors on capacity fade and impedance increase of graphite/NCA Li-ion batteries over accelerated aging tests. Test protocols (cycling and check-up) are presented, and the behavior of battery under aging is described. An equivalent-circuit model is used to extract the various contributions of the impedance spectra. Finally, the influence of the aging factors on capacity fade and impedance increase is discussed.

Lithium-ion state of charge observer with open circuit voltage hysteresis model

This paper deals with a state of charge (SOC) observer for a lithium ion battery, based on a Kalman filter and on the main electrochemical phenomena modeling. In this paper, a method to consider the hysteresis phenomenon on the Open Circuit Voltage has been developed and included into a SOC observer.

A method for the fast estimation of a battery entropy-variation high-resolution curve – Application on a commercial LiFePO4/graphite cell

Abstract The entropy-variation of a battery is responsible for heat generation or consumption during operation and its prior measurement is mandatory for developing a thermal model. It is generally done through the potentiometric method which is considered as a reference. However, it requires several days or weeks to get a look-up table with a 5 or 10% SoC (State of Charge) resolution. In this study, a calorimetric method based on the inversion of a thermal model is proposed for the fast estimation of a nearly continuous curve of entropy-variation. This is achieved by separating the heats produced while charging and discharging the battery. The entropy-variation is then deduced from the extracted entropic heat. The proposed method is validated by comparing the results obtained with several current rates to measurements made with the potentiometric method.

Thermal modeling and experimental validation of a large prismatic Li-ion battery

This paper deals with the thermal modeling and experimental validation of a large prismatic Li-ion battery. A lumped model representing the main thermal phenomena in the cell, in and outside the casing is proposed. Most of the parameters are determined analytically, using physical and geometrical properties. The heat capacity, the internal thermal resistance and interfacial thermal resistance between the cell and its cooling system are experimentally identified. The proposed model is validated with a precision of 1°C.

Temperature dependency modelling of LFP/C battery for an aeronautical application

Batterys modelling for an aeronautical application is presented in this paper. An electric equivalent circuit model is chosen to represent batterys behavior and is identified with a large characterization test matrix using a LiFePO4/graphite cell. Temperature dependencies have been then modelled using Arrhenius law for some of models parameters in order to lighten their lookup tables for further implementation in real-time applications. The validity of the resulted model is later evaluated, for a presumed aeronautic load profile, in order to test its capability in ensuring the required specifications.

LiFePO 4 /graphite battery modelling for an aeronautical application

This paper presents a generic study of batterys modeling in aeronautic field. A model identification protocol is discussed at first, the validity of the model is then evaluated, using a LiFePO4/graphite cell, for a presumed aeronautic load profile in order to test its capability in ensuring the required specifications.

On-line adaptive tuning of a lithium-ion battery cell state of charge observer

This paper deals with the adaptive tuning of a state of charge observer for a lithium ion battery cell, based on an extended Kalman filter and on the main electrochemical phenomena modeling. A high level parameter to tune the observer is introduced and used to reduce the influence of modeling errors on the state of charge estimate.