Online parameter estimation for lithium-ion battery by using adaptive observer for fractional order system

Due to the prevalence of Li-ion battery, the importance of the battery management system (BMS) is increasing. BMS is the system for managing the operation of batteries and monitoring their state of health. By using the observer containing parameter estimator for analyzing the equivalent circuit model of batteries, the online diagnosis of the batteries becomes possible. However, the Li-ion battery has complicated dynamics derived from the Warburg impedance which described the diffusion phenomena of the Li-ion. Applying fractional calculus to the expression of the system, the dynamics of Warburg impedance can be described simply. By designing the adaptive observer which can treat the system described as fractional order system, it is expected to become possible to identify equivalent circuit containing Warburg element online without approximation. In this paper, we designed the Kreisselmeier type adaptive observer for the linear fractional order system. Then, we applied the proposed observer to the half-cell of the lithium-ion battery modeled by Randles circuit under semi-infinite linear diffusion, and confirm the effectiveness of proposed adapitve observer by numerical simulation.