The use of wind power has taken an enormous rise and is on the step to a large-dimensioned technical use. This development was started by the progress in wind power plant technology and is characterised by an increase of output, thus linked with a reduction of costs and remarkable improvement of reliability.
Larger and larger wind power plants (0.5 MW – 2.5 MW) and wind parks in the range from 10 to 100 MW are connected even to weak grid areas in order to exploit the available wind potential. In future, therefore, apart from improvements of grid compatibility also controlling, conducting and regulating methods as well as the introduction of systems for failure prediction will open new aspects. Thus, with increasing rated power of the plant a clear tendency towards technologically innovative systems can be recognised in the MW-Class. By speed-variable operation with active and reactive power control it is possible to reduce stresses in the drive train and to improve the compatibility with the public mains.
Worldwide, wind energy is almost exclusively used for producing electricity. With regard of the energy transmission to electrical supply companies they have to observe differences between systems with limited feed-in facilities which occur in insulated operation or by supply to weak grids, and the connection with rigid public mains with an unlimited capacity for feed-in.
Wind power plants are required to enable a reliable operation in both fields of application. Further the reactive power supply with pulse-controlled inverter reduces the reactive power demand from the grid. Pulse-controlled inverters as power-factor controller also allow an active voltage control of the mains voltage limits.
By plant- and grid-specific dimensioning it is possible to connect more wind power plants, than without voltage control, especially in strong wind areas with weak dead-end feeder. The acceptable voltage fluctuations and flicker can be kept usually at small expenditure. Costs of measures for grid reinforcement can be saved thus to large extent.