In 2017, Energinet and TenneT, the Danish and Dutch Transmission System
Operators (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 turbines
and several HVDC links transmitting this power to the onshore grids. This
project brings together new opportunities and new challenges, both from a
technical and economic point of view. In this regard, this paper presents three
analyses regarding the design and operation of such an offshore system. First,
we perform a techno-economic assessment of different grid configurations for
the collection of the power produced by wind farms and its transmission to the
hub. In this analysis, two frequencies and two voltage levels for the operation
of the offshore grid are investigated. Our findings show that the
nominal-frequency high-voltage option is the more suitable, as low-frequency
does not bring any advantage and low-voltage would results in higher costs. The
second analysis is related to the differences in operating the system with low-
or zero-inertia; different dynamic studies are performed for each configuration
to identify proper control actions and their stability properties. Comparing
the outcomes of the simulations, we observed that voltage and frequency
oscillations are better damped in the zero-inertia system; however, the risk of
propagating offshore faults in the connected onshore grids is mitigated with
the inclusion of the synchronous condensers. Lastly, a comparison of
ElectroMagnetic Transient (EMT) and phasor-mode (also known as RMS) models is
presented, in order to understand their appropriateness of simulating low- and
zero- inertia systems. The results show that phasor approximation modelling can
be used, as long as eigen-frequencies in power network are well damped.Comment: Submitted to "CIGRE Technical Exhibition 2020 - Session 48" on
January 3, 2020 - Revised on February 15, 2020 - Accepted on June 4, 202
