Novel High-Voltage High-Power DC-DC Converter for Offshore Wind Farms

This paper deals with offshore wind system with DC collector grid, in which a high-voltage (HV) DCDC converter is utilized between the DC collector gird and HVDC transmission line. This study is focused on the circuit configuration of the HV DC-DC converter. Conventionally, a modular multilevel converter (MMC) is used for AC-DC conversion in HVDC systems. However, adopting the MMC topology for the HV DC-DC converter cannot achieve high efficiency because of hard switching. This paper proposes a novel configuration of a 1-GW +/- 25-kV/+/- 350-kV dual-active bridge DC-DC converter for offshore wind system, which comprises two series-connected IGBTs to reduce the transformer weight and increase the efficiency. The proposed configuration can achieve the efficiency of 98.5%.