A High-Frequency Planar Transformer with Medium-Voltage Isolation: Preprint

Satyaki Mukherjee, Branko Majmunovic, Gab-Su Seo, Soham Dutta, Rahul Mallik, Brian Johnson, Dragan Maksimovic

Research output: Contribution to conferencePaper


This paper presents the design of a low-loss, high-frequency planar transformer having medium-voltage (10's of kV) isolation capability while transformer primary and secondary windings are interleaved to reduce losses. Medium-voltage isolation between adjacent printed circuit board (PCB) layers is extremely challenging using traditional PCB dielectrics. The isolation requirement is met using PCB with $7$\,kV/mil polyimide (Panasonic Felios RF775) as the dielectric, and by an appropriate layout of the windings and the inter-winding vias. The transformer is used to implement a dual active bridge (DAB) converter in a stackable dc-ac architecture where the dc port is connected to a photovoltaic (PV) string and ac outputs are connected in series to achieve direct PV string-to-medium voltage conversion without the need for low-voltage collection or a bulky line frequency transformer. Since each DAB transformer processes time-varying power, a design methodology is developed to minimize line-cycle-averaged losses. Experimental results are presented for a 1:1 planar transformer in a 7.5\,kW SiC-based dc-to-ac module operating at 200 kHz. Isolation of 26 kV between the primary and secondary layers and between the windings and the core is verified using a hipot tester.
Original languageAmerican English
Number of pages9
StatePublished - 2021
Event2021 IEEE Applied Power Electronics Conference (APEC) -
Duration: 9 Jun 202112 Jun 2021


Conference2021 IEEE Applied Power Electronics Conference (APEC)

Bibliographical note

See NREL/CP-5900-81219 for paper as published in proceedings

NREL Publication Number

  • NREL/CP-5D00-79583


  • insulation resistance
  • medium voltage
  • medium-voltage transformer
  • modular power conversion
  • planar transformer


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