Dear Jason,
I have few confusions regarding validation of linear system.
Background:
I have created MBC_A,MBC_B,MBC_C,MBC_D matrices through running getmats__f8 and mbc3 commands.
I took the avg of above mentioned matrices through "MBC_Avg(B,C,D) = mean(MBC_(B,C,D), 3)" commands respectively (is it correct to use this command in this particular case?).
Problem:
Now I created the statespace model in simulink and was trying to compare the outputs of openloop linear system with openloop nonlinear system but my outputs are not matching they are not even close.
Relevent Information:
I have gone through these two threads (viewtopic.php?f=30&t=1873&p=9536&hilit=linear+model+simulink+test#p9536) and (viewtopic.php?f=30&t=1593) thoroughly. The information i get from your posts there is as follows:
1: "linear model is defined in terms of perturbations about the operating point e.g. y = y_op + dy for system outputs, so, you should either add the operating point value (y_op) to the output of the linear model or subtract the operating point value from the output of the nonlinear for comparison."
2: "The linearized model output by FAST is only valid for small perturbations about the operating point. It looks like you want your operating point to be based on steady 10m/s wind. Thus, the windinput disturbance represents a deviation from 10 m/s; you are setting this disturbance to 10 m/s, which actually implies a wind speed of 10 + 10 = 20 m/s, so, it is natural for the linearized model output to differ from the steadystate FAST solution. Likewise for the other input, state, and output perturbations."
Questions:
1: As I have lineraized my system around 18 m/s, so If I apply 0.1 m/s wind speed as input to linear system then will it be considered 18.1 m/s for the system? (so on and so forth for every input)
2: In order to get my linear system validated, should I add my respective nonlinear output into my linear output? e.g. y = y_op + dy (as in my case: nonlinear Gen Speed (rpm)+linear Gen Speed (rpm) should be compared to nonlinear Gen Speed (rpm)).
Note: To compare rotating outputs I have to apply inverse MBC transform.
Best Regards
Syed Shah
Validation of Linear System
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Re: Validation of Linear System
Dear Syed,
Yes, I agree that MBC_AvgB can be calculated as mean(MBC_B,3) etc.
Regarding (1), "yes," if the wind speed operating point is 18 m/s, then a perturbation of 0.1 m/s results an effective wind speed of 18.1 m/s.
Regarding (2), you should add the linearized output (dy) to the operating point output (y_op) for comparison to the nonlinear solution (y) i.e. y = y_op + dy.
I hope that helps.
Best regards,
Yes, I agree that MBC_AvgB can be calculated as mean(MBC_B,3) etc.
Regarding (1), "yes," if the wind speed operating point is 18 m/s, then a perturbation of 0.1 m/s results an effective wind speed of 18.1 m/s.
Regarding (2), you should add the linearized output (dy) to the operating point output (y_op) for comparison to the nonlinear solution (y) i.e. y = y_op + dy.
I hope that helps.
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
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

 Posts: 12
 Joined: Mon Aug 28, 2017 4:17 pm
 Organization: University of Paderborn
 Location: Germany
Re: Validation of Linear System
Dear Jason,
Thank you for your quick help and clearing my doubts.
Best regards
SS
Thank you for your quick help and clearing my doubts.
Best regards
SS
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