Creating transfer function with a variable gain "k"

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Helge
Helge on 30 May 2011
Answered: Prajith S A on 22 Aug 2022
Let's say we have a variable gain "k" in series with H(s)=(s*0.5-1)/(s*(s+1)^2), how may I get the complete transfer function with the variable K in matlab out of this? I don't want to use simulink.

Answers (4)

Robert
Robert on 1 Oct 2016
This problem was never really solved and now i have the same one. How do you handle this? You create a transfer function with tf function but it does not allow for adding gain?
Makes no sense to me

Yamac Tan
Yamac Tan on 16 Apr 2020
Edited: Yamac Tan on 16 Apr 2020
I have the same problem right now but I cannot find an exact solution. I have a closed loop negative feedback model with the static gain as "K" on the upper branch. I need to show "Input/Output = Transfer Function" with the variable "K". Still makes no sense.
  2 Comments
Paul Kroemer
Paul Kroemer on 29 Oct 2020
I have the same Problem right now, so i wanted to ask if you found a solution for it? Thanks for your help.

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Paulo Silva
Paulo Silva on 30 May 2011
K=1:10
sys=K*H(s) %replace H(s) with your transfer function
sys(1) is your system with gain K=1 and so on until sys(10) -> K=10
you can also use functions like the step
step(sys) %this will plot your system response to a step for each gain K
  5 Comments
Paulo Silva
Paulo Silva on 30 May 2011
If you have the symbolic toolbox take a look at this
http://www.mathworks.com/matlabcentral/answers/6355-how-do-i-get-the-coefficients-of-this-symbolic-expression
Paulo Silva
Paulo Silva on 30 May 2011
For your example
syms K s
T=K*(1-s)/s^3+s^2+s+K
pretty(T)

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Prajith S A
Prajith S A on 22 Aug 2022
s = tf('s'); % Assign variable s, as variable of the transfer function
sys = (s+1)/(sˆ2+2*s+1)
s = zpk('s');
sys = (s+1)/(sˆ2+2*s+1) % Returns transfer function in factored form

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