18 System description
Control of generator power
The generator power can be controlled by adjusting torque or speed:
where
P generator power (W)
T generator torque (N·m)
angular speed of the generator (rad/s)
n rotor mechanical speed (1/min rpm).
In normal operation, the converter controls the generator torque. However, either a torque
or an active power reference to the converter is supported. The overriding wind turbine
controller (WTC) gives a torque reference (or an active power reference) to the converter
that generates a specific torque on the generator shaft. The overriding wind turbine
controller defines the needed torque/power reference as a function of wind speed and
turbine characteristics. A typical wind turbine power vs. speed curve is presented below. It
illustrates the operational speed range of the turbine between the cut-in and cut-out
speeds. Cut-in speed is the minimum wind speed at which power generation is
reasonable. Cut-out speed is the maximum operating speed that the wind turbine system
can tolerate. In the example below, the generator is for 1700 rpm and 2400 kW.
Wind speed (m/s)
05 10
15
20
25 30 35
0
1200
1300
1400
1500
1600
1700
1800
1900
2000
0
400
800
1200
1600
2000
2400
2800
3200
3600
Generator rotor speed (rpm)
Cut-in speed
Cut-out speed
Power optimization
Power limitation
Turbine power delivered to electrical power network (kW)
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