Design and Control Strategies for a 25 kW LLC Converter with a Wide Output Voltage Range Comprising Distributed Core Transformers

Abstract This paper presents the design and experimental validation of a 25 kW LLC converter for a 50 kW electric vehicle (EV) fast charging system (FCS) module, emphasizing a broad output voltage range. The resonant network of the LLC converter is analyzed to ensure optimal operational efficiency, and the half-bridge control method is explored to accommodate extensive voltage range. The converter features a distributed core transformer, focusing on the evaluation of connection methods for enhanced power density and efficient heat dissipation. Based on these analyses, an LLC converter optimized for efficient operation was developed. Experimental verification on a 25 kW testbed confirms the effectiveness and validity of the proposed design and control methods, demonstrating their substantial applicability for high-power EV charging.