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How to replace Linear system with its response function.

Hello, colleagues.

I have response function (RF, see pic.) of some part of a linear system in form (input/output)/frequensy or I can represent this function by real, imaginery at frequency. I need to delete this part from a full model and represent it by submodel from signal library. 

What submodel from sygnal library I shoud use to represent this deleted part? I tried to use dynamic response function submodel but it doesnot fit well to my RF. I heard it is possible to use real and imaginery parts of RF, but i cant fined appropriate submodel in signal library. Please help me.

6 REPLIES

Re: How to replace Linear system with its response function.

Hi Vitalii,

 

in LMS Imagine.Lab Amesim you have the possibility to import linear models (menu Modelling > Import linear model in sketch mode).

 

The supported files types are:

  • .jac files which are created from a linear analysis in LMS Imagine.Lab Amesim
  • .ssp files whic represent the state space system of a linear model. You can create such a file from a script (in Matlab, Python, VBA or Scilab) calling the function tf2ame or ss2ame
  • >> help tf2ame
     TF2AME Save transfer function in an external file readable by AMESim 
     
     	Save transfer function :
     
                             NUM(s) 
                     H(s) = --------
                             DEN(s)
     
            in an external file readable as an AMESim special submodel.
     
     	NUM and DEN must contain the coefficients of the numerator and
     	denominator in descending powers of s
     	
     	TF2AME(NUM,DEN,'FILENAME') save  transfer function in file FILENAME 
     
     	TF2AME(NUM,DEN) without third argument the default file name 
     	is TRANSF.ssp
     
      	See also ss2ame, ameloadj, fprintf, control system toolbox
    
    >> 
    >> help ss2ame
     SS2AME Save state space matrix system in an external file
            readable by AMESim 
     
     	Save State-space system :
                     .
                     x = Ax + Bu
                     y = Cx + Du
     
            in an external file readable as an AMESim special submodel.
     	
     	SS2AME(A,B,C,D,'FILENAME', X) save state-space matrices A,B,C,D
     	in file FILENAME along with the values of the state variables X.
     
     	SS2AME(A,B,C,D,'FILENAME') save state-space matrices A,B,C,D
     	in file FILENAME.
     
     	SS2AME(A,B,C,D) without fifth argument the default file name 
     	is STATSP.ssp.
     
      	See also tf2ame, ameloadj, fprintf, control system toolbox.
    

Best regards

Re: How to replace Linear system with its response function.

Thank you for your support.

But I think first what I have to do the interpolation of that transfer function (see pic. above) into two polinominal functions. After that i will have all coefficients wich I shoud to put into ft2ame function. I am right?

Re: How to replace Linear system with its response function.

[ Edited ]

 


vitalii wrote:

Thank you for your support.

But I think first what I have to do the interpolation of that transfer function (see pic. above) into two polinominal functions. After that i will have all coefficients wich I shoud to put into ft2ame function. I am right?


 

Indeed,

 

I thought you already had the transfer function coefficients. If you don't have them yet, then indeed you will first have to interpolate your curve.

 

Best regards

Re: How to replace Linear system with its response function.

Okay.

Thus I do not have to use tf2ams (using VBA, for ex.). Having interpolated that TF I'll put all coefficient to appropriate amesim's submodel. I guess its name is dynamic transfer function. There on the icon are two polinoms. 

Do you know how to interpolate that curve (on pic.)? Is there such a function?

 

Re: How to replace Linear system with its response function.

[ Edited ]

Hi vitalii,

 

I think you have to look at "system identification" methods.

There is such a toolbox in Matlab. If you have access to it, it may help you to go from your transfer function to its linear representation.

 

I hope this helps.

Re: How to replace Linear system with its response function.

I have spent days trying to solve this problem. I found what that function on a pic is a response function (Ampl/frequency with a lot of poles) not a transfer function, and it is impossible by using interpolation replace the linear system with it. 

In this case I have to use 2nd order lag, maybe a few, and manualy look other they coefficients, trying to fit their summ responce to one what I need.

I am I right?