Variable Turns-Ratio Matrix Transformer based LLC Converter for Two-Stage Electric Vehicle Auxiliary Power Module Applications

An auxiliary power module (APM) is needed in electric vehicles, which converts traction battery voltage (270430V) to the low voltage auxiliary system (12.5∼15.5V). The single-stage design may achieve high power density but will suffer from poor efficiency and wide input voltage regulation capability. The design with two-stage can achieve wide-range regulation and good efficiency but will suffer from low power density. In order to achieve high efficiency while maintaining a good power density, a variable ratio matrix transformer based LLC is proposed to replace the fixed ratio transformer based LLC-DCX stage in two-stage AMP. The variable turns ratio matrix transformer reduces the low-side copper losses via the adaptive number of element transformers. Additionally, the buck stage achieves better efficiency with the variable intermediate bus voltage. As a result, it is potential for the system to reduce the cooling requirements with high-efficiency power conversion. A 1.6 kW prototype achieves 97.21% peak efficiency with 1.8 kW/L power density.