Environmental Engineering Reference
In-Depth Information
be required to perform functions not demanded from present onshore wind farms.
1
Such
functions will include:
control of active and reactive power;
system frequency control;
local grid voltage control;
operation under abnormal conditions such as grid faults;
contribution to network stability.
These requirements will demand signifi cantly improved sophistication of wind turbine and
wind farm control functions. Although the majority of the current multimegawatt wind tur-
bines operate at variable speed using a doubly fed asynchronous generator some experts
believe that this arrangement is not optimum if stricter utility requirements have to be satis-
fi ed. Compared with full power converters such as those in gearless wind turbines, doubly
fed arrangements are more problematic because during fault situations they can inject large
peak currents into the system.
If the ICORASS design is a true representation of future wind turbines, its permanent
magnet synchronous machine can only be interfaced to the grid through a full power converter
which, in addition to the utility requirements listed above, will have the added task of braking
the wind turbine above rated wind speeds to enforce stall regulation power control. Future
wind turbine designers will not be short of challenges!
A Proposed European DC Supergrid
The VSC based HVDC technology can be adapted to operate with several terminals on the
DC side so that power can be injected or extracted at will at each terminal. This proposed
mode of operation has encouraged feasibility studies for a European DC supergrid. Because
of the concentration of the wind power resource in the Atlantic, the North Sea and the Baltic,
there has been a suggestion that such a grid would be highly benefi cial (see, for example,
Reference [3]). It would range from Scandinavia down to France and would link Germany,
the UK, Ireland and Spain on the way, as shown in Figure 8.3. The cost of such an enterprise
would be substantial but it has been calculated that it would be more cost-effective than the
upgrading of the existing onshore networks necessary to absorb the large available offshore
potential.
Another advantage would be the considerable aggregation of the resource over a very large
geographical area, resulting in a much fi rmer resource in spite of local variations. Addition-
ally the system would have the ability to provide energy to the country with the greatest need
at specifi c times and the possibility of using the grid as an interconnector between national
markets to enhance energy trading. This is particularly attractive because of the time
1
Indeed, a number of these requirements are incorporated into recent Grid Codes, for example those of E.ON
Netz, Germany (Grid Code High and Extra High Voltage, E.ON Netz GmbH Bayreuth, August 2003, http://www.
eon-netz.com), National Grid, UK (The Grid Code, Issue 3, Revision 19, January 2007) and EirGrid, Ireland (Grid
Code V2,0, April 2007).
