Offshore wind is the fastest-growing segment of renewable energy. Integrating offshore wind farms, that are far from the shore, into the power system requires High Voltage Direct Current (HVDC) technology and converter stations. This results in the displacement of conventional power generation, lower system inertia and lower short circuit capacity of the AC system. The AC grids integrated with multiple converters in a close electrical vicinity have the potential to influence each other. The interoperability and stability of the system with a large number of converters is regarded as a key issue in the future power system planning development.

The Sofia and Dogger Bank C interaction studies investigate the reciprocal interaction between the two projects, which will be operated on the AC onshore side in a close electrical vicinity. The risk-analysis focuses on negative interactions that can cause a deterioration in network performance, potentially leading to system instability, such as:

• Control loop interaction ;
• Interaction due to non-linear functions ;
• High frequency interaction (harmonics and resonances).

The connection of these two projects is unusual. There are two very powerful HVDC links, rated at 1320 MW and 1200 MW respectively, that will be connected at the same electrical location simultaneously by two different HVDC manufacturers, Hitachi Energy and GE’s Grid Solutions.  As a third party, RTE international ensures that the intellectual property of the respective stakeholders remains protected. The studies will use offline EMT simulation methods, as well as in-the-loop hardware, with replicas of both projects being hosted in RTE international’s laboratories in Lyon.