North Sea Wind Power Hub: System Configurations, Grid Implementation and Techno-economic Assessment.

In 2017, Energinet and TenneT, the Danish and Dutch Transmission SystemOperators (TSOs), have announced the North Sea Wind Power Hub (NSWPH) project.The project aims at increasing by 36 GW the North Sea offshore wind capacity,with an artificial island collecting all the power produced by wind turbinesand several HVDC links transmitting this power to the onshore grids. Thisproject brings together new opportunities and new challenges, both from atechnical and economic point of view. In this regard, this paper presents threeanalyses regarding the design and operation of such an offshore system. First,we perform a techno-economic assessment of different grid configurations forthe collection of the power produced by wind farms and its transmission to thehub. In this analysis, two frequencies and two voltage levels for the operationof the offshore grid are investigated. Our findings show that thenominal-frequency high-voltage option is the more suitable, as low-frequencydoes not bring any advantage and low-voltage would results in higher costs. Thesecond analysis is related to the differences in operating the system with low-or zero-inertia; different dynamic studies are performed for each configurationto identify proper control actions and their stability properties. Comparingthe outcomes of the simulations, we observed that voltage and frequencyoscillations are better damped in the zero-inertia system; however, the risk ofpropagating offshore faults in the connected onshore grids is mitigated withthe inclusion of the synchronous condensers. Lastly, a comparison ofElectroMagnetic Transient (EMT) and phasor-mode (also known as RMS) models ispresented, in order to understand their appropriateness of simulating low- andzero- inertia systems. The results show that phasor approximation modelling canbe used, as long as eigen-frequencies in power network are well damped.