Pitch to stall mode for controlling the NREL 5MW reference turbine

Dear Dr. Jonkman,

I am working on designing and implementing a (Hinf or gain-scheduled) feedback controller for the NREL 5MW baseline turbine (described in [1]) on a semi-submersible platform. Currently, I focus on regulating both the generator speed and the platform motion in Region III. I understand that the baseline turbine is designed to work in pitch-to-feather mode and the baseline gain-scheduled PI controller introduced in [1] is consistent with this. However, in my simulations, I found I could get better performance in terms of generator speed and platform motion regulation under pitch-to-stall mode than under pitch-to-feather mode. I just wonder whether it makes sense to use pitch-to-stall mode for my control purpose.

Thank you. Look forward to your reply.

Best
Boran

[1] Jonkman, Jason, et al. “Definition of a 5-MW reference wind turbine for offshore system development.” National Renewable Energy Laboratory, Golden, CO, Technical Report No. NREL/TP-500-38060 (2009).

Dear Boran,

I looked at pitch-to-stall control for floating offshore wind turbines at one point…see: nrel.gov/docs/fy08osti/42589.pdf.

Best regards,

Dear Dr. Jonkman,

Thank you very much for your quick response. I have another question. In Page 9, Section II. B of the paper you listed above, there is the following paragraph.

Does this mean that, when we simulate a pitch-to-stall controller in FAST, we need to manually do the same modifications as what you did above?

Thanks.

Best
Boran

Dear Boran,

It is been so long since I wrote that report that I cannot remember the effect of the smoothing, but certainly the stall characteristics of an airfoil are important for pitch-to-stall-regulated turbines.

You can find the smoothed airfoil data in my post dated Sep 26, 2017 in the following forum topic: http://forums.nrel.gov/t/nrel-5mw-rotor-geometry/330/15.

Best regards,

Dear Dr. Jonkman,

Thanks again for your clarification. I found the modified airfoil data files in the post you provided. Here I wonder whether those files are exclusively for stall mode or they can also be used for feather mode as well. This concern is related to whether I need to switch between different files when I switch between stall and feather modes.

Thanks.

Best Regards
Boran

Dear Boran,

I’m sure you can use the same files for both pitch-to-stall and pitch-to-feather studies. I can’t remember the effect of the smoothing on the pitch-to-stall study, but certainly the stall characteristics are more important for pitch-to-stall-regulated turbines. You could always run a few cases using both sets of data to see the influence yourself.

Best regards,

Thanks for your quick reply. Really appreciate your patient help!

Best Regards
Boran