Power flow participation by an embedded HVDC grid in an interconnected power system

Renewable electric energy generation is continuously increasing worldwide. Because of its climatic basic requirements for efficient operation there will only be a few spots for renewable bulk power generation. While locations of load centers will not change significantly and power generation will likely be decentralized, the average distance between them will considerably increase. Simultaneously, the demand for bulk power long distance transmission grid is increasing. One possible solution is an HVDC based meshed overlay (MTDC) grid. An essential inherit capability of MTDC grids is controllability of its ac/dc coupling points. Thus ancillary services as load frequency control have to be actively sustained by pro rata load flow participation of the MTDC grid to continuously ensure system stability. To participate in those and other load flows, a method for MTDC grids is presented. Numerical case studies show that a MTDC overlay grid with the developed operating scheme relieves the ac grid by an adjustable amount of power flows and improves the load frequency control e.g. in terms of faster fault clearing and smaller frequency deviations.