I have few confusions regarding validation of linear system.
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?).
Now I created the state-space model in simulink and was trying to compare the outputs of open-loop linear system with open-loop nonlinear system but my outputs are not matching they are not even close.
I have gone through these two threads (http://forums.nrel.gov/t/fast-linearization-model-in-simulink/1381/1) 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 10-m/s wind. Thus, the wind-input 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 steady-state FAST solution. Likewise for the other input, state, and output perturbations.”
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.