High efficiency design approach of a LLC resonant converter for on-board electrical vehicle battery charge applications

Abstract

In this study, an optimal design procedure of inductor-inductor-capacitor (LLC) resonant converter for on-board electrical vehicle (EV) battery charge applications based on high efficiency is proposed. In the design procedure, lithium-ion battery cells are used due to their high power density, higher voltage and current rates compared to a lead-acid battery cells. Thus, LLC resonant converter should be regulated the output voltage in a wide voltage range with different load conditions according to typical charging profile of lithium-ion battery. For the design procedure, basic operation characteristics of LLC resonant converter is defined and operation regions are discussed in terms of high efficiency. The operation regions of LLC resonant converter are discussed to regulate wide output voltage range. In order to reach high efficiency optimal design, efficiency calculations based on Saber simulation are extracted for discussed operation regions. The best efficiency values are obtained for the operation of above-below resonance. Finally, soft switching operation of the LLC resonant converter is validated by Saber simulation for wide output voltage range and with changing load current.