Flexible HF distribution transformers for inter-connection between MVAC and LVDC connected to DC microgrids: Main challenges

Solid-state transformers or so called flexible high-frequency (HF) distribution transformers are likely to become a more efficient inter-connection between medium voltage (MV) AC grids and low voltage (LV) DC grids which can eventually be connected to DC microgrids. This paper addresses the main challenges in order to implement this technology. High-Frequency Transformers (HFTs) are one of the key elements of such converters which are the main contributor to realize the voltage adaption, isolation requirements, as well as high-power density. This paper addresses the essential design considerations taking into account the magnetic materials, leakage inductance integration as well as thermal management of such transformers. Moreover, the limitations of the currently available semiconductors are discussed and the applicability and performance of the latest generations of 10 kV SiC MOSFETs are discussed. The highlighted design considerations within both the transformer and HV SiC devices are then demonstrated using experimental results.