A 100 kW, 405 kHz HFT for Power Electronic Building Blocks (PEBBs) with a Compact MV Electrical Insulation Design

A 100 kW, 405 kHz high frequency transformer (HFT) for a CLLC-based solid state transformer (SST) is proposed featuring a planar winding structure and compact insulation design for electric ship applications. A split-core, 1000 V in \1000 V out design is realized using a standard U-core shape, separated by a 3 mm mica sheet to provide medium-voltage (MV) electrical isolation. Field grading techniques commonly used in MV cables and power modules are applied to increase the partial discharge inception voltage (PDIV) of the sheet and overall transformer. Litz wire is employed to form a pair of parallel, un-potted coils across the transformer, doubling its current-carrying capability while supporting forced-air cooling. This transformer design aims to address the significant challenge of maintaining a reduced transformer size at > 200 kHz for MV systems where high electrical isolation requirements and high-power operational points usually necessitate increased insulation thickness and large cooling systems. A preliminary 50-kW prototype is demonstrated for proof of concept, achieving 98.7% efficiency with 144 W of winding loss and 484 W of estimated core loss. The thermal performance is also evaluated for the proposed design at both 50-kW and 100-kW. The development of improved MV insulation sheets is also presented which achieved a PDIV of ≤ 8 kV on test coupon sheets, a 56% increase from the initial transformer prototype.