Testing increasing pitch in control region 2.

Hello,

I am using FAST through MATLAB, simulating the NREL 5MW reference turbine. My goal is to study the effect of wind farm control on an array of 3 aligned turbines. Right now I’m focusing on the impact of applying axial induction control strategies by changing the pitch on 1 turbine, on both energy production and loads.

To do so, I started with the Cert19 example, and changed the Simulink open loop model, so the pitch controller takes an input variable. Then, I ran several consecutive simulations with different pitch settings supplied to the blades, ranging from 0 to 5º, with steps of 0.5º. The simulations were done with a wind profile generated by TurbSim, with wind speed = 8 m/s and turbulence intensity = 6%. But I ran into a problem.

The next picture shows the results of such simulation. On the right is the labels of the columns of the left table. For pitch settings of 1.5º or higher, both the power and thrust coefficients drop tremendously. This is not expected at all, since based on figure 2 of article “Comparison of Actuation Methods for Wake Control in Wind Plants” (Gebraad 2015, attached), both coefficients should decrease as de pitch decreases, not drop abruptly.

To understand what is happening, I decided to plot the angle of attack along the blade, for pitch = 0º,1º and 1.5º. Below I show the plot for output node 3 on blade 1.

There are severe oscillations on the angle of attack along the blade. What is happening here? What should I do to properly test the effect axial induction control on control region 2?

I am thankful for the time taken reading this post, and any help you migth be able to provide.

Manuel Ramos
Comparison of Actuation Methods for Wake Control in Wind Plants.pdf (1.12 MB)

Dear Manuel,

I would not expect this behavior either. I’m not sure what the problem might be.

Do you see large oscillations in other FAST outputs e.g. control actions or turbine deflections?

Which version of FAST are you using and which aerodynamic model have you enabled?

Best regards,

Dear Jason,

I do see oscillations in other outputs, e.g. lift and drag coefficents, Mach number. The total rotor aerodynamic load and generator speed drop significantly and oscillate as well. The generator torque oscillates greatly. However, the blade pitch (as outputed by ElastoDyn and AeroDyn) stays constant and at the correct value, inputed by my script.

I am using FAST V8, and AeroDyn V15. Below I supply a link for my github repository where I have my code.
https://github.com/Allistor21/wind-farm-control-investigation

Best regards,

Manuel Ramos

Dear Manuel,

I only looked briefly at your input files. One problem could be that you are controller torque from the DISCON DLL, but pitch from Simulink. However, the DISCON DLL has logic for both torque and pitch and the logic is interrelated. Because your pitch is controlled by Simulink, the torque computed by the DISCON DLL may be getting corrupted. I would first check that the simulation response is as you expect without control by disabling the generator degree of freedom in ElastoDyn (GenDOF = False) with a prescribed (fixed) rotor speed (RotSpeed).

Best regards,

Dear Jason,

I tried your suggestion, and it worked well. I disabled the generator degree of freedom in ElastoDyn, and set the rotor speed to be fixed at the rated speed of 12.1 rpm. The system behaves as expected, and there are no more oscillations. Thank you for your acute suggestion.

Best regards,

Manuel Ramos