Dynamic study of resonant converters for lithium-ion battery charger applications

Abstract

This paper presents the design and modeling of a charger for LiFePO4 lithium-ion batteries based on a two-phase resonant converter. The high capacity 48 V battery is fully characterized and modeled by its electrical parameters. In order to study the interaction of the charger with the battery during the charging process, an envelope model of the resonant converter is developed. The converter ac model reaches up to the tens of kHz bandwidth range to study the interaction with the battery including the dependence on the transport and diffusion phenomena. Also, the large bandwidth of the current-mode operation of the converter qualifies it to carry out an effective battery diagnosis. The envelope model enables efficiently the long-time simulation of the charger-battery system, providing a tool for evaluating the control performance as well as the variation of the battery variables along the charging process. The theoretical and experimental results are in good agreement.