Dear Jason,
I’m afraid I have some more questions. The simulation result from the previous post were obtained for still water conditions. In this post, I am attaching similar graphs for two cases with regular waves. One has Tp=10s and Hs=1. The other one has Tp=33 and Hs=1. The second one is really a crash test case because the 33 period is close to my spar platform natural frequency in roll and pitch, but the one with Tp=10s is close to real conditions prevailing in my localization (Hs can be much greater, but the Tps range from 6 to 11s for the measurement data I am planning to compare against later).
My questions:
-In the picture named Torque Regions, I have an indicator of the current torque region of the controller. When the turbine is in region 3 for a still water case, but close to rated power production, for the case with wave excitation, there is rapid switching of torque regions. this is for times t: 600<t<900.
What could be done to prevent this changing of torque region?
-When the turbine is in the linear region with respect to the rotational speed of the shaft( region 2.5. Times t 400<t<600s.) The torque sensibility to the wave excitation seems to be greater than for region 2 just before. What could be the reason for that?
If you find some time to have a look at these plots, your opinion would help me a lot.
Thank you,
BS
Tp_33s_Hs_1m.zip (255 KB)
Tp_10s_Hs_1m.zip (176 KB)
Dear Bartosz,
I’m not sure I fully understand what you are doing. As far as I could tell, you are assessing the steady-state response at 3, 11.4, 13, and 15.5 m/s by running one long simulation with slow wind-speed ramps in between. I’m not sure what you are plotting in the Torque Regions.png images; these appear to be hand calculations of the torque in various control regions rather than an actual OpenFAST output; is that correct? Which control settings have you used within the OpenFAST simulations?
I’m not sure what you “ripple” you are referring to.
In your zipped figures, again, I’m not sure what you are plotting in the Torque Regions.png files; the torques here don’t seem to match what I assume is the OpenFAST output plotted in Generator.png.
The torque can jump quickly if the torque-speed curve is very steep, which I would not recommend. In the transition region between Regions 2.5 and 3, the torque controller is often limited to maintaining Region 3 torque if the blade-pitch angle is above some threshold (even if the generator speed falls into Region 2.5) so as to avoid toggling often between Regions 2.5 and 3.
You can linearize the OpenFAST model at any point in time, but the linearized solution is most useful when the model is in (periodic) steady state.
Best regards,
Dear Jason,
The Torque Regions is the output from the scope with the same name, from the Simulink torque control. I’m attaching a graph print. The second scope is used to produce the ‘blow-up’ image.
Thank you for taking the time to answer.
I like the idea to use the blade pitch angle to stay in Region 3. I guess this was the initial purpose of having it in the model of torque control. I just didn’t quite grasp that before. (input 2 in the graph is blade pitch. I guess I’ll have to calibrate it better in the condition for region 3 or work more on pitch controller…
By ‘ripple’ I mean the jump in torque when control switches to region 2.5. In the graphs from previous posts that happens when time is 400s. I’ll Try to change slopes as you have suggested.
Best Regards,
BS
Torque Controller.pdf (47.4 KB)