NOWITECH Annual Report 2015

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Annual Report 2015 28 NOWITECH Norwegian Research Centre for Offshore Wind Technology
processes and technology in development.#14 and Figure 11.
Another topic that has been in focus in 2015 is
the possibility for extending the range for HVAC
transmission. With the uncertainties and high
costs of HVDC
transmission,
the well-known
and trusted
AC option is
attractive to
many wind
farm developers also for long distances. Research
in NOWITECH has applied detailed power cable
models to investigate how the transmission
distance can be extended by smarter choice of
transmission voltage, see also Table 6: New models,
methods, processes and technology in development.#13.
The 2015 NOWITECH Innovation Award was
given to Sverre Gjerde and Pål Keim Olsen for
the development of a modular, high-voltage,
transformerless generator/converter for a wind
turbine. This research was conducted in WPC.
Figure 11 Operation of long distance HVAC trans-
mission cable at variable voltage can give signifi-
cant efficiency improvements. The figure is for a 200
km, 220 kV, 1000 mm2 cable.
type, using detailed modelling techniques. The
study is important since such phenomena are
not easily captured by simplified models and can
potentially lead to very costly repairs.
WPC research activities are part of international
collaborations through coordination with related
work in European research projects, such as
IRPWIND, EERA-DTOC, and BestPaths. Moreover,
NOWITECH scientists are strongly involved in
EERA JP Wind sub-programmes for offshore wind
and grid integration, as well as having a leading
role in the new IEA Wind Task 37.
Methods to supply wind energy to offshore oil and
gas platforms has been a big activity in NOWITECH
in previous years and these results are now being
brought forward in a new IPN project with Statoil.
Another 2015 spin-off related to WPC is a new
KPN project considering reliability and rugged-
ness of high power high voltage power electronics
(RELIPE).
In order to understand the dynamics of a wind
farm as a complete system with interactions
between aerodynamic, hydrodynamic,
mechanical, electrical, and control domains it
is necessary to have an integrated description
formulated in a way that allows analytical tools
to be applied. This is achieved with the linearised
state space model (STAS) that is being developed
in NOWITECH. Using STAS, frequency domain
analyses for the entire system is possible,
something that is very useful for example for
developing wind farm control strategies, see
also Table 6: New models, methods, processes
and technology in development. #12.
In large offshore wind farms, there are clear
benefits of increasing the voltage level from 33
to 66 kV, which is reflected in an industry move
in this direction. However, the change in voltage
affects the electrical properties of the wind farm
grid, shifting resonance frequencies. In order to be
able to predict and avoid harmful harmonics and
other electrical interactions, wideband models for
66 kV wind farm grid components are developed
and applied, see also Table 6: New models, methods,
Another topic that has been in
focus in 2015 is the possibility
for extending the range for HVAC
transmission.