Blade pitch control

This forum if for discussing controls. Questions about how to implement controls in FAST are more appropriate to the CAE Tools forum.

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KumaraRaja.Eedara
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Re: Blade pitch control

Postby KumaraRaja.Eedara » Fri Nov 29, 2019 1:46 pm

Dear all,

I am trying to implement a simple pitch controller in FAST using MATLAB (Simulink). However, I observe discrepancy in the pitch angle between MATLAB and FAST.out. Kindly note that here i am not using two different controllers in FAST and MATLAB. I am simply setting PCMode to 4 in servodyn.dat file and using the controller as given in the figure "PitchController.Jpg" (attached) and performing the simulation . I could successfully track the generator speed at fixed value above the rated speed. When I plot pitch activity reported in the FAST output file,(pitch_FAST.jpg) it does not match with the same I plotted through scope variable "pitch angle" in simulink (pitch_MATLAB.jpg). I expect a difference of units i.e FAST output in deg and MATLAB in radians but i see a significant difference in both, can some one help me the reason for this difference. Thanks.

PS: I understand that this sort of pitch activity is meaning less, nevertheless, both FAST and simulink output should match. Right?

Regards,
Kumara
Attachments
Pitch_MatLab.JPG
Pitch_MatLab.JPG (39.46 KiB) Viewed 870 times
pitch_FASTOUT.jpg
pitch_FASTOUT.jpg (29.73 KiB) Viewed 870 times
PitchController.JPG
PitchController.JPG (55.28 KiB) Viewed 870 times

zarei.atefe
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Re: Blade pitch control

Postby zarei.atefe » Fri Nov 29, 2019 3:06 pm

hi every one
How much should be used to the value of time constant of the 1.5 MW wind turbine pitch actuator for the FAST reference turbine?

Jason.Jonkman
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Re: Blade pitch control

Postby Jason.Jonkman » Mon Dec 02, 2019 3:09 pm

Dear Zarei,

By "1.5-MW wind turbine...for the FAST reference turbine" are you referring to the WindPACT 1.5-MW baseline turbine? The documentation for this turbine (WindPACT Turbine Rotor Design Study: https://www.nrel.gov/docs/fy06osti/32495.pdf) refers to a second-order blade-pitch actuator (with a given natural frequency and damping ratio) rather than a time constant of a (presumably) first-order actuator that you are asking about.

Based on our separate e-mail communication, can I assume that you now have the FAST-Simulink interface working?

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

Jason.Jonkman
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Re: Blade pitch control

Postby Jason.Jonkman » Mon Dec 02, 2019 3:19 pm

Dear Kumura,

The FAST-S-Function will use extrapolated values of the inputs (including blade-pitch angle) passed from Simulink (as discussed in other forum topics e.g. viewtopic.php?f=4&t=1985&p=10496 and viewtopic.php?f=30&t=1720&p=8155). Thus, the FAST S-Function may not report exactly the same values of the blade pitch angles that are input from Simulink. I would always ensure that (1) the initial pitch angle set within the ElastoDyn primary input file matches the pitch specified within the Simulink model at time zero and (2) the pitch angle changes are defined smoothly within Simulink.

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

zarei.atefe
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Location: iran

Re: Blade pitch control

Postby zarei.atefe » Tue Dec 03, 2019 3:16 am

thanks for your help.
i read it. There, it is said that ωn = 4Ω, where Ω is the rotor angular velocity and I've considered 20,463 rpm for the rotor speed and it is said ξ = 80% of critical damping. I want to know how much the critical damping value is?

Yes i am working FAST-Simulink interface now.

best regards.

Jason.Jonkman
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Re: Blade pitch control

Postby Jason.Jonkman » Tue Dec 03, 2019 6:42 am

Dear Zarei,

In general, for a simple single degree of freedom second-order system of the form m*xdd + c*xd + k*x = 0, the natural frequency is omega_n = sqrt(k/m) and the critical damping is c_c = 2*sqrt(k*m) = 2*m*omega_n. While the paper specifies omega_n, it is unclear what mass/inertia (m) is used. I would guess that it is the rotor inertia (m = RotIner) or full drivetrain inertia (m = RotIner + GenIner*GBRatio^2).

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

Zhe.Zhang
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Organization: Harbin Engineering University
Location: China

Re: Blade pitch control

Postby Zhe.Zhang » Mon Mar 23, 2020 7:03 am

Dear Dr. Jonkman,
I'm designing a pitch controller and I need to know the state of the wind turbine. Based on the degrees of freedom I set, I extracted Q_GeAz and QD_GeAz from the output, which represents the Displacement of variable speed generator DOF and Velocity of variable speed generator DOF, respectively. I connected a differentiator to Q_GeAz in Simulink, I think its output should be consistent with QD_GeAz, but the actual gap is very large, please help me
Second question: If I want to extract all the states, can I only extract them from the outlist, and cannot use the differentiator in simulink
Thanks
Attachments
Related documents.zip
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Jason.Jonkman
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Re: Blade pitch control

Postby Jason.Jonkman » Mon Mar 23, 2020 7:29 am

Dear Zhe.Zhang,

Numerical derivatives produce noisy results and I would generally avoid them when possible. With Q_GeAz this is particularly true because Q_GeAz is reduced by 2pi whenever it exceeds 2pi (otherwise Q_GeAz will continue to increase and get very large over time), and so, the numerical derivative calculation must be changed near zero and 2pi.

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

Zhe.Zhang
Posts: 26
Joined: Wed Apr 03, 2019 1:40 am
Organization: Harbin Engineering University
Location: China

Re: Blade pitch control

Postby Zhe.Zhang » Mon Mar 23, 2020 8:02 am

Dear Dr. Jonkman'
Do you mean that I'd better use the form 'u (strmatch (' QD_GeAz ', OutList))' when extracting the state related to the derivative?
Thanks

Jason.Jonkman
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Re: Blade pitch control

Postby Jason.Jonkman » Mon Mar 23, 2020 8:12 am

Dear Zhe.Zhang,

Yes, it would be better to use QD_GeAz directly from the simulation than to try to calculate by taking a numerical derivative of Q_GeAz.

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

Zhe.Zhang
Posts: 26
Joined: Wed Apr 03, 2019 1:40 am
Organization: Harbin Engineering University
Location: China

Re: Blade pitch control

Postby Zhe.Zhang » Mon Mar 23, 2020 8:16 am

Dear Dr. Jonkman
Does the value of 'QD_GeAz' (Velocity of variable speed generator DOF) indicate the generator speed, but through my comparison in simulink, they are not the same.
Thanks

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Blade pitch control

Postby Jason.Jonkman » Mon Mar 23, 2020 10:35 am

Dear Zhe.Zhang,

Output QD_GeAz from ElastoDyn is the rotational speed on the low-speed shaft end of the gearbox. Multiplying QD_GeAz by the gearbox ratio (GBRatio) will give the generator speed.

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


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