Electrical - Wind Energy: Renewable Energy and the Environment - page 145

FIGURE 7.16 Controller for 50 kW wind turbine with induction generator, constant-rpm operation.
A management system would integrate the wind farm SCADA, on-site meteorological data, wind
forecasting, and market price to enable operators to maximize energy production and the income
from that production. Control strategies are proprietary as manufacturers pursue wind turbine
operations to maximize energy production within the wind regime and to minimize wear and
tear during very high winds.
7. 4 . 2 P OWER E LECTRONICS
Power electronics convert the variable-frequency and voltage power from the generator to the util-
ity grid, constant frequency and voltage within the ranges set by the utility to ensure power quality.
Converters are classified by AC to AC without a DC link (output voltages are chopped from input
voltages) and by AC to AC with a DC link (input voltages are converted into intermediate DC volt-
ages that are stored and then converted to the output voltages).
An overview presents the types of three-phase AC-AC converters [13]. For large wind turbines,
the power electronics allow them to operate more efficiently. For the doubly fed wound induction
generator, a common system is where the converter is connected to the rotor of the generator and
directly controls currents in the rotor windings so the mechanical and electrical rotor frequencies
are decoupled. Only a fraction of the rated generator power passes through the converter, 20-40%.
The operational speed range of the generator depends only on the converter rating.