Power not stabilizing in region III

[marc-schwa]

Hi all,

I am facing a problem with a synthetic fixed offshore turbine based on the IEA 15MW that I am working with. I am new to this universe of controller tuning so my question might be trivial. I modify the model but once I try to tune the controller, I am getting unexpected results. The behavior of the controller in region II is acting as expected. However, there is something happening between the transition of region II to region III. As seen below, when the turbine is transitioning between the two regions, the power keeps raising while the thrust stabilizes and keeps a constant value until the cut-out wind speed. The axis labels are correct, and the thrust seems to unexpectedly follow the shape of the power curve. The normalized values I am using are based on the reference values that I was expecting the turbine to achieve at rated.

Checking the plot of the blade pitch and rotor speed, I could see that the rotor speed maintains a behavior similar to what I would be expecting. The blade pitch though seems to be very acting very slowly

Naturally, I followed the idea of first generating the performance file, to then tune the controller and finally perform the Openfast simulations. I am using openfast 3.5.2 with ROSCO 2.9.0.

Here it comes my question: Any recommendations on parameters or adaptations that could be applying for achieving a behaviour closer to the reality? For reference, here is the YAML file I am using (without the modified turbine parameters):

[dzalkind]

If the rotor speed is constant and the power is increasing, I suspect then your generator torque is increasing. Can you show that?

Have you set a maximum torque value for this turbine that is different than the IEA-15MW? Ideally, the torque would saturate at this maximum value in above rated conditions.

It doesn't appear like you've changed anything in the controller parameters, but the turbine parameters are very important for determining the gains, set points, and saturation limits of the controller.