I have a unknown system in simulink model (non-linear) and I dont know how to get a TF which will describe it in certain interval of input data. Im sorry that im asking such abstract question but im really lost.
I tried 'tfest(data,number_of_poles,number_of_zeroes)' Also I tried 'ident' and then import input and output into ident GUI and then click estimate TF. Both returned me transfer function which behave completly different than my system.
Im not really sure what input should i generate into system, should the imput be noise? I would appreciate any kind of advice or help here.
If you have Simulink Control Design, you can use the Frequency Response Estimation functionality or linearise your Simulink model around an operating point.
You probably need to provide more information (data, code, etc...) as to why tfest and ident didn't work. There are a lot of different models and options available within the system identifcation GUI, it may just be a matter of choosing the correct one.