PCB-Winding Integrated Transformer for 800-V Dual Active Bridge Converter using 1.2-kV GaN Devices

This paper introduces a novel PCB-winding integrated inductor-transformer for an 800-V Dual Active Bridge (DAB) converter. This isolated dc-dc converter implements 1200-V GaN transistors for their introduction in a next-generation onboard charger. Using 1200-V GaN devices omits the need for complex and expensive multi-level topologies using 650-V GaN devices and challenges the well-established 1200-V SiC devices in the onboard charger application. The newly developed split-PCB integrated inductor-transformer eliminates the series inductor and addresses key design challenges in high-voltage, high-frequency converters, such as parasitic capacitance mitigation. An optimal transformer is achieved through a hybrid optimisation procedure that combines analytical and finite element calculations. Limitations due to parasitic capacitances, which are inadvertently high in PCB winding transformers, are detailed and mitigated through three optimised transformer prototypes. A novel design approach achieves the target leakage inductance by tuning the turns and degree of interleaving in the PCB windings. Furthermore, experiments and simulations provide a comprehensive comparative analysis between the different transformer prototypes. Finally, these are implemented in two distinct proof-of-concept dual active bridge converters with 1200-V GaN transistors, highlighting challenges in implementing these novel technologies. The results underline the potential of PCB-winding integrated magnetics and 1200-V GaN devices towards high-performance yet cost-effective automotive converters.