Environmental Engineering Reference
In-Depth Information
Figure 5.36
Operating Points for a Wind Turbine with Two Asynchronous
Generators with Different Speeds
Synchronous generator with direct mains coupling
The synchronous generator does not have the disadvantage of requiring a
certain reactive power demand since this can be controlled by the excitation
current. Therefore, a synchronous generator can both generate and consume
reactive power. Permanent magnets can also be used to excite the synchronous
generator. In this case, reactive power cannot be controlled. Furthermore,
permanent magnets are rather expensive. Hence, power electronic components
such as thyristors usually convert the three-phase current of the mains to the
desired DC that determines the excitation (see Figure 5.37).
In contrast to the asynchronous generator, the synchronous generator runs
with a constant speed. The operation characteristics in the speed-power
diagram are indicated by an absolutely vertical line that has no slight bend at
higher powers as with the asynchronous generator. The slip cannot cushion
power jumps so that they pass almost entirely to the mains. Besides changes in
load at the mains, this can cause high mechanical strains on the wind generator
itself. A slip clutch can cushion gusts but also exhibits high wear.
Rotor
Excitation
Gearbox
SG
Transformer
Generator
Grid
Figure 5.37
Synchronous Generator with Direct Mains Coupling
