How to chose one form of transfer function from other forms
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Hi,
I want to generate the transfer function of an induction motor by using its caracteristic matrix (A,B,C,D):
syst=ss(A,B,C,D)
[num,dem]=tfdata(syst)
h=tf(num,dem)
but I get 4 from of transfer function h because I have 2 inputs in my system :
h =
From input 1 to output...
60.54 s^3 + 1.003e04 s^2 + 4.953e08 s - 1.133e11
1: ------------------------------------------------------
s^4 + 318.4 s^3 + 8.206e06 s^2 - 3.742e09 s + 4.281e11
-6.605e07 s - 3.266e08
2: ------------------------------------------------------
s^4 + 318.4 s^3 + 8.206e06 s^2 - 3.742e09 s + 4.281e11
From input 2 to output...
6.605e07 s + 3.266e08
1: ------------------------------------------------------
s^4 + 318.4 s^3 + 8.206e06 s^2 - 3.742e09 s + 4.281e11
60.54 s^3 + 1.003e04 s^2 + 4.953e08 s - 1.133e11
2: ------------------------------------------------------
s^4 + 318.4 s^3 + 8.206e06 s^2 - 3.742e09 s + 4.281e11
Continuous-time transfer function.
I want to use this command :
sys=ss(tf(h))
but I need to choose one of these transfert functions.
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Réponses (1)
Paul
le 18 Déc 2020
Modifié(e) : Paul
le 19 Déc 2020
You don't need to get the num and den explicitly using tfdata (unless you need them for some reason). To convert from ss to tf:
h = tf(syst)
h is a transfer function matrix that you can index into to pick what you want. For example, a state space realization for the transfer function from the first input to the second output is:
sys = ss(h(2,1))
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Paul
le 20 Déc 2020
Walter's solutions should work. One clarification: I believe that step always returns y with as many rows as in t, even for systems with a single output.
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