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How to replace Linear system with its response function.

Creator
Creator

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.

1.png

6 REPLIES

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

Siemens Genius Siemens Genius
Siemens Genius

Hi Vitalii,

 

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

LMS Amesim - [CUsersmsiy4wDesktopElevator_no_SC.png

 

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.

Creator
Creator

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.

Siemens Genius Siemens Genius
Siemens Genius

 


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.

Creator
Creator

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.

Siemens Phenom Siemens Phenom
Siemens Phenom

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.

Creator
Creator

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?