Inquiry regarding Power Fluctuations of GSPI Controller under 18m/s Turbulent Wind in OpenFAST

[lk73438702]

Dear everyone,
I hope this email finds you well.I am currently testing the NREL 5MW baseline GSPI controller in OpenFAST. Under an 18 m/s turbulent wind condition, I noticed that after the simulation reaches steady state(t > 100), the generator power fluctuates above the rated 5 MW line, occasionally creating spikes up to 5.5 MW or higher (as shown in the black/red curves below). I would like to ask: Is this level of power fluctuation normal for the standard GSPI under such high turbulence? Is it mainly because the blade pitch rate limit restricts the controller from shedding the aerodynamic loads fast enough, or does it mean my simulation setup has some issues?Any insights from your side would be greatly appreciated!
Best regards,

[lk73438702]

[jjonkman]

Dear @lk73438702,

Presumably by "GSPI", you are referring to a gain-schedule proportional-integral controller; is that correct? Are you running the OpenFAST model of the land-based NREL 5-MW baseline wind turbine from the r-test (https://github.com/OpenFAST/r-test/tree/main/glue-codes/openfast/5MW_Land_DLL_WTurb) with its baseline DISCON controller (https://github.com/OpenFAST/r-test/tree/main/glue-codes/openfast/5MW_Baseline/ServoData/DISCON)? If so, what you have changed relative to the model available from the r-test?

Best regards,

[lk73438702]

Dear @jjonkman ,
Thank you for your reply. To clarify, I have not made any modifications to the baseline NREL 5-MW land-based model or the DISCON controller from the r-test repository
However, during peer review, a reviewer pointed out that in my results, the generator power remains above the rated 5 MW even after reaching a steady-state condition above-rated wind speeds.
Since I am using the un-modified benchmark setup, I am wondering if this steady-state offset is a known numerical characteristic of the baseline controller, or if it might be a post-processing oversight on my part (e.g., plotting aerodynamic rotor power RotPower instead of electrical generator power GenPwr, or not simulating long enough for the GSPI controller to fully settle).
Any insights on whether the baseline GenPwr should settle strictly at 5.00 MW under steady winds would be immensely helpful.

Best regards,

[jjonkman]

Dear @lk73438702,

Presumably you only changed the wind conditions in InflowWind and the initial conditions in ElastoDyn?

Can you clarify what power output you are plotting?

Best regards,

[lk73438702]

Dear @jjonkman
Thank you for your reply.
I only changed the wind conditions in InflowWind
Regarding the output: I can confirm that I am directly plotting the electrical generator power, GenPwr, not RotPower.
So, just to clarify: is it true that GenPwr should never remain above 5.00 MW in a true steady-state condition? If it does, does it mean my simulation results are indeed incorrect ?
Best regards

[jjonkman]

Dear @lk73438702,

I don't see that you are computing a steady-state condition, but under turbulent or stepped inflow, I would expect the baseline controller for the NREL 5-MW turbine to allow GenPwr to exceed 5 MW for short periods of time. I would not expect GenPwr to exceed 5 MW under true steady-state conditions, with steady inflow above rated.

Best regards,