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

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

Postby Boran.Zhao » Tue Jan 01, 2019 8:50 pm

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).

Jason.Jonkman
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Re: Pitch to stall mode for controlling the NREL 5MW reference turbine

Postby Jason.Jonkman » Wed Jan 02, 2019 8:22 am

Dear Boran,

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

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Boran.Zhao
Posts: 12
Joined: Wed Feb 14, 2018 9:52 am
Organization: University of British Columbia
Location: Canada

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

Postby Boran.Zhao » Wed Jan 02, 2019 8:04 pm

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.

Before pursuing the design of the pitch-to-stall controller, I decided to smooth the airfoil-data coefficients (as
presented in Ref. 2) near stall to eliminate the existing fluctuations that could have led to numerical problems in the blade-element / momentum (BEM) aerodynamic-induction solution algorithm. I modified the airfoils by manually manipulating the lift coefficients.


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

Jason.Jonkman
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Re: Pitch to stall mode for controlling the NREL 5MW reference turbine

Postby Jason.Jonkman » Wed Jan 02, 2019 8:20 pm

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: viewtopic.php?f=2&t=440&p=9944.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Boran.Zhao
Posts: 12
Joined: Wed Feb 14, 2018 9:52 am
Organization: University of British Columbia
Location: Canada

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

Postby Boran.Zhao » Thu Jan 03, 2019 8:37 am

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

Jason.Jonkman
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Re: Pitch to stall mode for controlling the NREL 5MW reference turbine

Postby Jason.Jonkman » Thu Jan 03, 2019 8:58 am

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,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Boran.Zhao
Posts: 12
Joined: Wed Feb 14, 2018 9:52 am
Organization: University of British Columbia
Location: Canada

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

Postby Boran.Zhao » Thu Jan 03, 2019 10:38 am

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

Best Regards
Boran


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