Study the Thermal Performance of the CLLC Transformer in the OBC Designed Using SiC MOSFETs

The CLLC resonant converter topology is becoming increasingly popular in the on-board chargers (OBC). At the same time, the superior material characteristics of wideband gap devices enable a higher switching frequency design with improved power density. However, the higher power density enabled by the higher frequency brings new challenges for designing the transformer in CLLC topology. The thermal performance analysis of the transformer is paramount to evaluate its performance and to ensure the reliability of the CLLC. This paper analyzes the loss of the transformer in detail. Meanwhile, the thermal performance of the transformer under different working conditions is illustrated. The temperature trend of the transformer is mainly related with the switching frequency and input voltage of the CLLC resonant converter. Finally, a high power density 6.6kW OBC experimental platform, which is designed using 1200V/50A Fuji SiC-MOSFETs, is built to verify the temperature trend of the transformer.