Preliminary study on voltage level standardization of DC grid based on VSC-HVDC technology in China

Large Offshore wind farms are planned in China and some are under constructions. DC grid or multi-terminal HVDC is the promising technology to delivery large offshore wind power over long distances. DC grid voltage levels need to be built to design optimal DC grid, without this voltage levels, DC grid may be sub-optimal, not cost-effective. This paper proposes the study framework of building voltage level of DC grid based on VSC-HVDC technology. In this framework traditional HVDC and existing VSC-HVDC projects are reviewed, technical limits and perspectives of DC grids are assessed, the economy of each voltage grade is compared to present the applicable range of DC grids system. Finally application examples of different DC voltage levels are analyzed in some typical DC grids and the future problems of DC grids development are discussed.