Hi Ravi,

There are several types of turbine controls - both with active pitch control and without, as stated in the earlier replies.

But the fundamental reason for the assumption is that in most stability studies, onset of instability occurs before dynamics of the PAC becomes significant enough !

That is, by the time the network becomes small-signal unstable, the PAC shows virtually no change !! Being slow enough, the pitch angle may be assumed constant for such studies.

The approximation is a bit subjective, but mostly acceptable.

-Sanjay

To maintain constant angle of attack and maximum power output, a constant ratio of wind speed to tip speed is required, hence constant pitch angle.

To elaborate: for extracting maximum power, a varying rpm is needed, so with constant pitch, the rotor is used to measure wind speed, and wind speed = rotor speed is used to determine the exact amount of current to draw from the generator. Pitch is only required to change if rotor speed exceeds maximum allowed (usually tip speed limited by noise regulations, but can also be to limit axial force in special applications) and when stopping or starting.

Hi Ravi,

Wind turbines are classified into two main types, Stall regulated and Pitch regeulated wind turbines. Therefore, Pitch angle is used to control the power produced from a wind turbine. It is active when the turbine power reach the rated power, in this case, the baldes are pitched with constant pitch angle according to the wind speed to change the angle of attack and hence the power maintained at the same value (The rated one).

In some cases that prevent the collapse of the wind turbine becuase if the blade will also deflect more and might hit the Tower and others resaons also are applied.

Best regards

Mohamed

Hi Ravi,

There are several types of turbine controls - both with active pitch control and without, as stated in the earlier replies.

But the fundamental reason for the assumption is that in most stability studies, onset of instability occurs before dynamics of the PAC becomes significant enough !

That is, by the time the network becomes small-signal unstable, the PAC shows virtually no change !! Being slow enough, the pitch angle may be assumed constant for such studies.

The approximation is a bit subjective, but mostly acceptable.

-Sanjay

Thank you all of you for your valuable suggestions and special thanks to Sanjoy Roy sir because this is what exactly i am looking for. Thank you so much.