Wide bandgap devices are creating new challenges and opportunities for passives, especially the magnetics and high frequency (HF) transformers. In this seminar, the researchers from university, national lab and industry will present advanced design and applications of high frequency (HF) transformers in high power medium voltage (MV) converters. The magnetics and HF transformers must be tested and characterized at relevant scales and voltage. Scaled down cores and voltages enable material characterization, but do not consider component level impacts (resonances, dielectric breakdown and losses, scaled manufacturing and etc.,). Therefore, this presentation starts with a comprehensive review of core materials and their characterization systems. Then a review of modeling approach for magnetics, especially considering the HF nonsinusoidal waveforms in the actual applications, will be presented, followed by the session of HF transformer design and optimization. In addition several case studies will be presented to illustrate the design methodology and validate the performance of these high power HF transformers.