This master thesis is initiated by a project proposal from Vestas Wind Systems A/S which is one of the leading manufacturers of wind turbine systems in the world. The proposal deals with DC-DC connected offshore wind farms with a HVDC-link to the shore line which is a promising technical solution regarding the increasing demand of electrical power and the long distances between on- and offshore sites. The main goal is the development of steady state models of an entire wind turbine system with selected AC-DC converters between the generator output and DC-DC connection of the wind turbines.