Model verification

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Jason.Jonkman
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Re: Model verification

Postby Jason.Jonkman » Tue Jan 21, 2020 5:21 pm

Dear Sina,

I'm not sure I can comment as the response seems to be driven by your controller, which it sounds like you've implemented yourself. Can you clarify how you are applying pitch control and torque control?

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

Sina.Ameli
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Re: Model verification

Postby Sina.Ameli » Tue Jan 21, 2020 9:24 pm

Dear Dr. Jonkman,
Thanks for your reply. Actually, it is a simple PI control with a bias term that is exactly equal to the pitch angle at the operating point. However, let's get back to your PI control. Why is it settled very well for test 18 but not for test 24?
Generator Speed_PI.PNG
Generator Speed PI
Generator Speed_PI.PNG (82.39 KiB) Viewed 1420 times


The PI control in your document is for an offshore WT but it seems work well for an onshore WT! Is it because an onshore wind turbine's dynamics is different from offshore WTs, for example because of hydrodynamics and mooring system?

Jason.Jonkman
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Re: Model verification

Postby Jason.Jonkman » Wed Jan 22, 2020 6:05 am

Dear Sina,

There are two reasons for this difference:
  • The offshore systems has different dynamics (including low-frequency platform motions) than the land-based system.
  • Because of these lower frequencies, the gains in the blade-pitch controller for the offshore system were reduced relative to those from the land-based system. This is documented more in the OC3-Hywind spar specifications report: https://www.nrel.gov/docs/fy10osti/47535.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

Sina.Ameli
Posts: 75
Joined: Mon Oct 15, 2018 11:23 am
Organization: FSU
Location: Florida

Re: Model verification

Postby Sina.Ameli » Wed Jan 22, 2020 8:35 am

Dear Dr. Jonkman,

Thank you so much for sending me the document for the offshore WT. I reduced the gains, then oscillations seem reduced a little like this:

GenSpeed.JPG
Generator Speed
GenSpeed.JPG (102.79 KiB) Viewed 1402 times

Generator Torque.JPG
Generator Troque
Generator Torque.JPG (97.43 KiB) Viewed 1402 times

Power.JPG
Power
Power.JPG (76.63 KiB) Viewed 1402 times


Thanks,
Best regards,
Sina

Sina.Ameli
Posts: 75
Joined: Mon Oct 15, 2018 11:23 am
Organization: FSU
Location: Florida

Re: Model verification

Postby Sina.Ameli » Wed Jan 22, 2020 5:40 pm

Dear Dr. Jonkman,

I have another question. Recently, I have read a paper implementing a controller (pitch control) on a 5MW offshore WT and shows the following results:
Simulation results.PNG
Offshore WT simulation results
Simulation results.PNG (47.25 KiB) Viewed 1386 times


Now, I am confused. While I cannot get a settled response with NREL's PI control due to hydrodynamics, and mooring system, this paper shows a completely settled responses!
Besides, you told me that the three blade pitch angles are different for TEST 24 (offshore), while they are the same (collective) for Test 18 (onshore). Why are the above figures for the pitch angles the same if it is an offshore WT?!

Thanks,
Best regards,
Sina

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Model verification

Postby Jason.Jonkman » Wed Jan 22, 2020 9:08 pm

Dear Sina

The baseline controller used in Tests 18 and 24 are nearly identical, just with different gains. Both are for collective blade-pitch control, so, the pitch angles are the same between the three blades for both tests.

I don't think I can really comment on the plots you are showing because I don't know their source. And the response, of course, will depend on the type of offshore wind turbine (and corresponding natural frequencies), as well as the controller used. The NREL 5-MW baseline controller is just that--a baseline--and I'm sure changes to the controller can be made to improve its performance. But in steady conditions, the baseline controller will settle out to a constant value after the transients die out; for the floating OC3-Hywind system this will take a while due to the very low natural frequencies of the platform in surge and pitch.

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

Sina.Ameli
Posts: 75
Joined: Mon Oct 15, 2018 11:23 am
Organization: FSU
Location: Florida

Re: Model verification

Postby Sina.Ameli » Wed Jan 22, 2020 9:56 pm

Dear Dr. Jonkman,

Thanks, I really appreciate that you replied to my questions promptly at all time.

Best regards,
Sina


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