Cluster-based DC grid control strategies applied to a European offshore grid scenario

This paper presents a novel cluster-based approach for operation and control of multiterminal offshore high-voltage dc (HVDC) grids equipped with voltage source converter (VSC) technology. While conventional optimal power flow algorithms for ac transmission systems focus on minimizing generation costs, wind forecast uncertainties and future bulk power transfers preset by contracts between Transmission System Operators require new concepts for control of future offshore multiterminal dc (MTDC) grids. Based on already installed and future planned offshore wind farms in the North Sea, power generation of a wind farm for one time step using specific wind power curves including limited availability, wake effects and dynamic shut off as well as a method to allocate wind power plants to HVDC offshore converter stations are outlined. A sequential Newton Raphson acdc power flow algorithm was developed to cluster MTDC grids into different zones assuring an export of power from wind farm clusters to different control or market areas. The two main control objectives for MTDC grid operation are minimum grid transmission losses and fulfilment of guaranteed power transfers to specific market areas. To provide proof of the overall applicability, acdc power flow simulations were carried out on a specially developed future European Offshore Grid Scenario using real forecasted offshore wind speed data.