Observer Design for SOC Estimation of Li-ion Batteries Based on Electro-Thermal Coupled Model

Abstract

During a decade of electric vehicle market rapid growth, Lithium-ion batteries have played a leading role thanks to their high power and energy density. Nonetheless, they still face many challenges, such as the influence of the State of Charge(SOC), ambient temperature and current rates on their life cycle. 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 battery state of charge, surface and core temperatures. Knowing these three key factors ensures better control of the battery operation conditions to prevent excessive heat generation. The model is expressed in a state-space form to allow battery state estimation, SOC and thermal prediction. A simple state observer and a robust nonlinear state estimator for SOC prediction are presented and compared. Then a nonlinear observer for core and surface temperature is modeled, and the obtained results are discussed.