HE AIM OF WIND TURBINE SYSTEMS
DEVELOPMENT is to continuously
increase output power. A few
years ago, the rated output power of
production-type units reached 200 kW. By 1999,
the average output power of new installations
climbed to 600 kW. The largest series production
units today are specified to deliver 1.5-MW output
power (Table 1). It is anticipated that in the near future,
power rating of wind turbines will increase further,
especially in offshore applications. For
example, the prototype of a Nordex N80 with a rated
power of 2.5 MW was installed in March 2000 near
Aachen.
Many low-power wind turbines built to-date were
constructed according to the “Danish concept” (Fig. 1),
in which wind energy is transformed into electrical energy
using a simple squirrel-cage induction machine
directly connected to a three-phase power grid. The rotor
of the wind turbine is coupled to the generator shaft
with a fixed-ratio gearbox. Some induction generators
use pole-adjustable winding configurations to enable
26 operation at different synchronous speeds. However, at