Experimental Efficiency Comparison Between the LLC Resonant Converter and the Phase Shifted Full Bridge Converter Operating as Battery Chargers

DC-DC conversion in electric vehicle chargers can require a single or multiple stages depending on both electrical architecture and amount of processed power. When isolation is provided by an output stage, a unidirectional isolated DC-DC converter is required. Among the possible candidates, the LLC resonant converter and the phase shifted full-bridge (FSFB) converter show several advantages which has made them preferred choices in recent literature. This paper compares the efficiency of both converters on equal basis under the variable load conditions imposed by a cycle of the conventional constant-current constant-voltage (CC-CV) charging protocol. To support the study, scale-down experimental prototypes of both converters have been implemented and evaluated in laboratory showing the superiority of the LLC resonant converter for almost the entire range of operation.