A Solid-state transformer (SST) directly reduces medium voltage to low voltage (e.g. 400 V) with minimized power conversion stages. Insulation structure is the bottleneck of DC-DC module in SST from insulation effectiveness, manufacturing process, thermal management, and power density point of view. In this digest, a compact PCB-winding transformer structure is proposed to handle the medium voltage insulation by FR4 in PCB-winding. The primary side winding is built in PCB-winding form and the secondary side winding is still Litz for a lower loss. With semi-conductive shielding and stress grading layer design, the E-field can be restrained in the primary side PCB for a partial discharge-free insulation. An arc section winding structure is proposed to reduce the high E-field inside the insulation layer. The layer-to-layer winding loss and overall loss/footprint trade-off is analyzed in detail to improve the performance. Finally, the design is demonstrated on a 200-kHz CLLC converter with 98.6% peak efficiency and 130W/in3 power density. The transformer can also achieve partial discharge free up to 14kV.
