Comparative Study of a Multi-MW High Power Density DC Transformer with an Optimized High Frequency Magnetics in All-DC Offshore Wind Farm

Artikel i vetenskaplig tidskrift, 2016

In this paper, the design of a 1/30 kV, 10 MW modular isolated DC-DC converter is presented. The design and optimization of a high frequency transformer as the key part of such a converter is addressed. Efficiency curves for different semiconductors and frequencies are presented in order to find an optimum frequency enabling adequate transformer volume reduction with a suitable compromise with the converter efficiency. It was found that for this voltage level and size, it is no point to go above 6 kHz from the transformer perspective since the isolation requirement leads to that the size is not reduced much more for even higher frequencies. At 5 kHz, the efficiency of the transformer having a nanocristalline core reached 99.7% while the power density was about 22 kW/l. For the whole DC-DC converter, an efficiency of 98.5% was reached at 5 kHz switching frequency using SiC MOSFETs as switching elements while the efficiency when using IGBTs reached 97.2% at the same frequency.