Introduction
In the future, the DC-technology will be increasingly used in electric power systems. At present, the HVDC-technology is already used for the energy transmission over long distances and for the connection between offshore windfarms and the onshoregrid. In many cases of application, HVDC is the only reasonable alternative. In electric distribution grids, the share of converter-connected, decentralized power generation units, especially photovoltaic units and wind energy converters, will further increase as well as the ratio of converter-fed loads in the grid will rise. Hence, the DC-technology can be advantageous for medium-voltage distribution grids regarding technical and economical issues. The realization of the internal medium-voltage grid in an offshore-windfarm is assessed as a possible application for a medium-voltage DCgrid, which interconnects the dcbusses of the wind energy converter units with the central HVDC-platform. In this way, the convertion to the 50 Hz AC-voltage at the WEC units, the transformation of the 50Hz current and the rectification for the HVDC-connection can be avoided…
