Lithium-Ion Battery Monitoring and Observability Analysis with Extended Equivalent Circuit Model

Lithium-Ion battery (LIB) on-line monitoring based on the extended equivalent circuit model (ECM) has received considerable attention. However, up to now, only linear observability analysis has been studied. The main purpose of this paper is to derive observability conditions for the extended ECM. Firstly, the battery ECM is decomposed into two sub-models mathematically, because there is no mutual coupling relationship between the battery states. Then, for the nonlinear extended one, an observability analysis is conducted. It shows that the observability necessary conditions depend on the battery current, the initial value of the battery capacity and the square of the derivative of the open circuit voltage (OCV) with respect to the state of charge (SOC). Numerical simulations have been conducted and have successfully assessed these conditions.