Optimized Dual Transformer Wiring Method for High Efficiency Operation of a 25kW LLC Converter

This paper presents the design and experimental verification of a 25kW class LLC converter for a 50kW electric vehicle (EV) fast charging system (FCS) module with a wide output voltage range. The LLC converter is composed of two transformers to reduce power density, and the design of each resonant network is discussed based on the connection method of the transformers. Based on the designed resonant network, a loss analysis was conducted to determine the structure with the highest efficiency among the two transformer wiring methods. Experimental verification on a 25kW LLC converter testbed confirms the effectiveness and validity of the proposed design methodology.