Pitch and Torque Cntrl (Region 3)

[Jason.Jonkman]

Dear Muddassir,

Your power is likely going so high because:

• the generator torque in your model is constant for speeds higher than rated speed (Region 3 control),
• the aerodynamic torque is higher than the rated generator torque, and
• you don't have active blade-pitch control to reduce the aerodynamic torque at high winds to regulate the speed,

which means that the rotor will overspeed (and generator power will exceed rated) until the aerodynamic torque balances with the generator torque.

You'll need another means of control to operate in Region 3 e.g. active blade pitch control.

Best regards,

[Cheng.Zhang]

Dear Jason,

If I am well understood, there are 2 methods to get generator torque, (considering the turbine working in region 3)
first, constant torque: fix it at its rated value;
second, constant power: get the generator torque by calculating T = P_rated/Omega;

And I'm working on the floating wind turbine control in region 3. The control objectives are keep rated power output and reduce the platform pitch motion. Currently, the generator torque was fixed at rated, the single control input is the collective blade pitch (CBP) angle.

My question is:
Is it possible to use generator torque as the second input? i.e. do not use the constant torque and the constant power strategy. Then, I will get two control inputs, it might improve the controller performance.

Best regards,
Cheng

[Jason.Jonkman]

Dear Cheng.Zhang.

Yes, what you propose has certainly been done before. Varying the torque in Region 3 can be effective to mitigate vibrations of the drivetrain-torsion and/or tower side-to-side modes.

Best regards,

[Cheng.Zhang]

Dear Jason,

Thank you!

I'm confused that,
1). Do a high vibration of the drivetrain-torsion means a high variation of the rotor speed?
2). In my opinion, performance is highly related to the control algorithm.

If I introduce additional control input (generator torque), the control is different from the one only have a single input (blade pitch angle). Recall that in my case, the objectives are to keep rated power output and to reduce the platform pitch motion. I can compare the performance of power and platform pitch motion of the two controllers.
As for the vibrations of the drivetrain-torsion and/or tower side-to-side modes, since they are not my control objectives, I can only check it rather than controlling it. Hence, why it is effective to mitigate vibrations of the drivetrain-torsion and/or tower side-to-side modes.

Best regards,
Cheng

[Jason.Jonkman]

Dear Cheng,

My previous comment simply stated that I have seen combined blade-pitch and generator-torque controllers, but that the generator-torque is often used to mitigate drivetrain-torsion and tower-side-to-side vibrations. I would not expect control of the generator torque to have a strong influence on platform-pitch, but it may be useful to regulate rotor speed and power in Region 3 if the pitch controller is also tasked with mitigating platform pitch. I would suggest reviewing the literature on these matters. The work of Namik and Stol from around 2010 comes to mind, but there are likely many others as well.

Best regards,

[Cheng.Zhang]

Dear Jason,

Thank you!
Now, it is clear to me.

Best regards,
Cheng

[Cheng.Zhang]

Dear Jason,

I have a controller that reduced the platform roll by -20% and platform pitch rate by -25% comparing with GSPI.
But the DEL of tower base side-to-side and fore-aft moment almost same as GSPI. Is it normal?

best regards,
Cheng

[Jason.Jonkman]

Dear Cheng,

That sounds a bit strange, but I'm not sure I can comment on that for a general system.

Best regards,