Operation of DC series connected offshore wind farm by using tap changing transformer with MMC-HVDC

In order to overcome economic disadvantage of offshore wind farm, many kind of grid connection and operation methods have been researched and analyzed by authors from around the world. The DC series connection of offshore wind farm is a solution to reduce installation and management costs, because this topology doesn't require installation of offshore platform which play a role as substation or high voltage direct current transmission system(HVDC) converter station. However, the DC link voltage of DC series wind farm may not be constant in accordance with variable wind speed. And only one wind turbine must be able to generate high DC link voltage for stable power transmission. Therefore, this paper proposes the operation of DC series connected wind farm by using tap changing transformer with modular multilevel converter(MMC)-HVDC.