Design of Insulation Structure of High-Frequency Transformer Based on Electromagnetic-Thermal Coupling Analysis under Non-Sinusoidal Excitation

High-frequency transformer (HFT) plays an important role in the application of power electronic transformers in flexible AC/DC transmission. It is necessary to study the distribution of the electrical stress of the internal insulating material of the HFT under the non-sinusoidal excitation and optimize the adjustment of the insulating structure. In this paper, the electromagnetic characteristics of the internal insulating materials of HFTs under high-frequency non-sinusoidal square-wave excitation are analyzed and experimentally measured, and the breakdown characteristics of epoxy resin under 1kV, 10kHz bipolar oscillating square-wave excitation are obtained. The coupled electromagnetic-Thermal Multiphysics field simulation was carried out using finite element simulation software to obtain the electric and temperature field distribution of the insulating material inside the HFT when it is operated under different dv/dt conditions. The required insulation margin inside the transformer was calculated using experimental measurements and data fitting results, and the electric and temperature field distributions were obtained using the simulation software to optimize the insulation structure design. The results of the study can provide guidance for the insulation structure and design of high-capacity HFTs.