Electro-thermal coupled battery model : State of charge, core and surface temperatures estimation

Since their emergence, lithium-ion batteries have played a major role in the growing market of electric vehicles thanks to their characteristics in term of power and energy density. However, the battery expected lifetime is still under investigation since it is influenced by State of charge, temperature and current rates. Which makes battery states prediction and thermal management essential to improve the Li-ion battery performance. Combining a three-state equivalent circuit model and a two-state thermal model, this paper proposes a coupled electro-thermal battery model capturing the State of Charge (SOC), the battery surface and core temperatures. Aiming to control the battery usage and avoid heating, the model is expressed in a state space form in order to allow state estimation and then SOC and thermal effects prediction. A simple state observer and a Robust Non Linear state estimator for SOC estimation are presented and compared. Then a nonlinear observer design for core and surface temperature is modeled, and the results obtained are discussed.