How to display a tf function in the command window frm simulink??

I have a tf of a plant which i need the be pulled from the simulink for my matlab function. Is there any function/command which can help me automatically obtain the transfer function so that i can obtain the Characteristic equation for in my further program?

Lets say for my simulink transfer, i want the generator tf automatically being obtained during my online autotuning. See image below.

Any suggestion?? Thnk you for reading my query.

Nitesh

Answer 1

[Nitesh]

Ny help guys??

[@Johannes]

Hello Nitesh,

you have to change the date type of the variable in which get_param writes the num or den. For example

a = get_param('test_tf/TF', 'Numerator');

a =

[5 2]

num = str2num(a)

num =

5 2

H=tf(num,den);

H =

     5 s + 2
  -------------
  2 s^2 + s + 1

Continuous-time transfer function.

Regards, John

Answer 2

[Nobel Mondal]

If your model is loaded, you can access the parameter values for a block using "get_param" api.

Say, you have a model "myModel.slx" and you would like to get the coefficients of a "Transfer Fcn" block named "myTFBlock"

 >> load_system('myModel') % If your model is already loaded, skip this
 >> numeratorVal = get_param('myModel/myTFBlock', 'Numerator');
 >> denomVal = get_param('myModel/myTFBlock', 'Denominator');

Hope this helps. Thanks.

[Nitesh]

Thank you Nobel Mondal.

This solved half of my problem im having with. I would like to have a equation on the command window lets say in the s-domain. the get _param is fine i suppose bt not as expected output when i want it in S-domain.

s=fotf('s');
numeratorVal = get_param('online_sim2/TF', 'Numerator')
denomVal = get_param('online_sim2/TF', 'Denominator')

using the plant lets say the equation i want back from the simulink is 1/(s^2+2s+1)

bt when i use fraction order transfer function call as fotf, den i have some compution. using tf as in tf([numeratorVal],[denomVal]) doesnt work.

 the code is given below. 

plant=fotf([numeratorVal],[denomVal])

i want like this when i use the above command.

          1
    ------------
      s^2+2s+1

the total output is given below:

how can i get the equation in s-domain like a normal tf similar like in the simulink??? please help...

this is my simulink block.