In the last years the initiatives for promoting a large-scale offshore grid infrastructure in the North Sea have received a growing political support by European institutions. Pre-feasibility studies have already demonstrated potential technical and economic benefits of such an offshore grid for the connection of offshore wind farms, the electrification of oil rigs and the establishment of a pan-European electricity market.
The realization of an offshore High Voltage Direct Current (HVDC) transmission system based on Voltage Source Converters (VSCs) is already theoretically feasible, since the major components of such a grid are commercially available. Still, operation of a future complex multi-terminal HVDC grid represents a major knowledge need for the industry, since no similar configurations are in operation in Europe today.
Some of the main challenges for operation of a multi-terminal offshore grid are to ensure reliable and stable operation in a system with multiple controllable units and operating entities, and to design selective protection systems that can ensure operation of the remaining un-faulted system after a fault condition. In particular, operation of a DC transmission system where all power flow is controlled by power electronic converters can produce unexpected interactions between units and controllers, with potential impact on the stability and overall reliability of the system. The design of protection systems for large-scale multi-terminal HVDC systems is also limited by the lack of commercial DC breakers with suitable specifications and because protection strategies developed for traditional AC grids are not applicable. Thus, the stability and protection system design of multi-terminal HVDC grids are the main focus areas of this project.