A Review of High-Power Medium-Frequency Transformers in Medium-Voltage Power Electronics: State of the Art, Challenges, and Solutions

Medium frequency transformers (MFTs) have emerged as a key enabling technology in medium voltage (MV) power electronics systems, supporting applications such as solid state transformers (SST), power electronic traction transformers (PETT), medium voltage direct current (MVDC) power distribution. This review provides a comprehensive overview of high-power MFTs, focusing on their state of the art, applications, technical challenges, and current research solutions. The paper surveys key considerations including core materials, core shapes, winding technologies, winding structures, insulation considerations, dielectric materials, electric field stress grading materials, and cooling technologies. Specifically targeted at modern MV power electronics, this paper discusses the challenges and solutions in MFT insulation design and test. The topics include complex voltage stress and electric field distribution, partial discharge under medium frequency high dv/dt waveforms, and insulation test standards which are critical to enhance the performance, reliability, and development of high-power MFTs in MV applications.