An Improved Design Procedure for a 10 kHz, 10 kW Medium-Frequency Transformer Considering Insulation Breakdown Strength and Structure Optimization

Medium-frequency transformer (MFT) is an essential device in the smart solid-state transformer (SST) prototype. Compared with the well-defined principle design of magnetic core and windings in MFT, insulation issues are barely concerned. This article focuses on improved design optimization of an MFT, considering the main insulation strength and structure. Dielectric breakdown characteristics of epoxy resin insulating material were studied. An obvious reduction of dielectric strength occurred at high frequency and high temperature in thick samples, which is used for the design of insulation clearance and margin. Moreover, a modified insulation loss evaluation was used, involving the square wave with spike voltages. Through introducing a strategy of multilayered insulation in the windings, the insulation structure is optimized. A 10-kW, 10-kHz, 1-kV/750-V MFT used in the 10-kV SST system was designed by considering the insulation research. Finally, experimental verifications of the MFT performance were carried out by a resonant dc–dc converter. It appears that the optimized MFT exhibits low electric field, small temperature rise, and high efficiency at a 10-kW load. This research provides the basic principles for insulation design in high-voltage and high-power MFT.