Blade pitch control

Dear Raivis,

The main objective of a baseline blade-pitch control system is to regulate the rotor (or generator) speed. See section 7.3 of the NREL 5-MW specifications report for the development of a standard baseline pitch control system: nrel.gov/docs/fy09osti/38060.pdf.

More advanced pitch control systems may include additional actuation (e.g. independent blade pitch) and additional control objectives (e.g. reducing loads).

If the rotor-blades are eroding, the controller gains may not be as the designer expected and the controller would not perform optimally.

Best regards,

Thank you, Jason!

I will study the NREL 5-MW specifications report.

Best regards,

Raivis.Nikitins
Adaplab

Hi everyone
I’m working on individual pitch control and set PCMode to 4 to get the pitch command from the simulink controller but the pitch remains fixed to the final value of 2.6 and does not command the simulink. Where is the problem?
thanks

Dear Zarei,

Are you saying that you running FAST interfaced to Simulink, you’ve set PCMode=4, but the commands from Simulink are being ignored? Have you enabled the override pitch maneuvers (TPitManS(), PitManRat(), BlPitchF(*)), which override the commands from the controller?

Best regards,

No I did not enable these. I just set PCMODE to 4 and then run the simulation.

Dear Zarei,

And you are running the simulation from Simulink?

Best regards,

Yes, I’m running from Simulink.

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



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?

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: 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,

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. http://forums.nrel.gov/t/s-function-input-output-signal-mismatch/1502/2). 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,

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.

Dear Zarei,

In general, for a simple single degree of freedom second-order system of the form mxdd + cxd + kx = 0, the natural frequency is omega_n = sqrt(k/m) and the critical damping is c_c = 2sqrt(km) = 2momega_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 + GenInerGBRatio^2).

Best regards,

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
Related documents.zip (51.3 KB)

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,

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

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,

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

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,

Hello all
I have a question regarding the pitch controller of a 10MW semisub system
Currently the pitch controller of the simulink model seems to be working based on the PI controller parameters specified in the control file of the 10MW semisub file
The only problem I do not know how to activate this pitch controller at very low wind speeds (as currently it will compare the rotor speed with a reference value of 9.6RPM - rated value) and as such the system will not work at very low wind speeds
What advice would you give to overcome this issue?
Thanks for your time,
Cameron