In order to solve the problems of poor thermal stability and high frequency noise of transformer in traditional DC-DC converter, the medium frequency transformer in isolated DC-DC converter is designed and studied, which adopts 0.15 mm ultra-thin silicon steel sheet. Firstly, the magnetism of ultra-thin silicon steel is measured by using singlepiece silicon steel sheet measuring device, and the B-H curves and B-P curves at different frequencies are given. According to the magnetic measurement results, the electromagnetic scheme of three port medium frequency transformer is designed by AP method and applied the particle swarm algorithm to further design under the constraint of loss minimization. Secondly the three-winding transformer of DC-DC converter is optimized and simulated. The magnetic flux density, loss, temperature field distribution, output voltage and current waveform of the transformer under different working conditions are given. Finally, the 20 kW DC-DC converter was manufactured and the magnetic characteristics of the medium frequency transformer were experimented to verify the correctness of the proposed scheme.

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