Offshore wind farms are connected to land by HVDC cables, with voltage source converters placed at both ends. The power output of each turbine is collected as AC at a medium voltage level, meaning that each turbine has to contain an AC-DC-AC converter. A promising approach to reduce the size of related power conversion equipment and conversion losses is to make each of the turbines output power as DC at a medium voltage level, which can then be collected and stepped up at a HVDC platform. The turbine DC-AC converter could be replaced by a series-resonant DC-DC converter using a medium-frequency transformer to step up the voltage. The main benefit of operating in a higher frequency range is the reduction in size and weight of the equipment used. However, the new approach also brings additional challenges, such as the relatively narrow operating range of such a converter and high voltage and current stress on its components. This document contains theoretical analysis of such a circuit, component selection, control system design and circuit validation, both by simulation and a downscale hardware setup.