A high-performance AC excitation and measuring system for on-line estimation of Lithium-ion battery cells' internal impedance

Nowadays, there is a rapid increase in the use of Lithium-Ion batteries for many different applications, due to their superiority in terms of energy density, efficiency, and self-discharge rate. In this paper, a high-performance system for estimation of Lithium-ion battery cells’ internal impedance is presented. The main concept lies in the excitation of cells through a multi-sine controlled current signal, instead of using the time-consuming sequential harmonic injection. The proposed technique was implemented for a LiFePO4, 3.2V/30Ah battery cell through a bi- directional power converter, for integrating both charging and discharging capability. A laboratory prototype of this converter was designed and implemented, to investigate theoretical assumptions. The experimental results are eventually analyzed, to evaluate the influence of the various experimental conditions on the cell internal impedance.