MATLAB Answers

How to create a transfer function system model from code with given parameters?

5 views (last 30 days)
I want to replicate a transfer function system model I created with tfest in code.
Here is the model I want to replicate.
>> tf21 = tfest(data_est,2,1,'Ts',1)
tf21 =
From input "u1" to output "y1":
0.9614 z^-1
----------------------------
1 - 1.663 z^-1 + 0.8313 z^-2
Name: tf21
Sample time: 1 seconds
Discrete-time identified transfer function.
Parameterization:
Number of poles: 2 Number of zeros: 1
Number of free coefficients: 3
Use "tfdata", "getpvec", "getcov" for parameters and their uncertainties.
Status:
Estimated using TFEST on time domain data "data_est".
Fit to estimation data: 84.81%
FPE: 1.025, MSE: 1.013
>> tf21.Numerator
ans =
0 0.9614
>> tf21.Denominator
ans =
1.0000 -1.6634 0.8313
Here's what I tried:
>> numerator = [0 0.9614];
>> denominator = [1.0000 -1.6634 0.8313];
>> tf_si = tf(numerator,denominator,'ts',1)
tfsi =
0.9614
----------------------
z^2 - 1.663 z + 0.8313
Sample time: 1 seconds
Discrete-time transfer function.
This doesn't look right. I need the same function that maps inputs to outputs. How do I set the coefficients for z^-2 and z^-1 on the denominator so they are the same as in the model I am trying to replicate?

Accepted Answer

Star Strider
Star Strider on 4 Feb 2020
Try this:
numerator = [0 0.9614 0];
denominator = [1.0000 -1.6634 0.8313 0];
tf_si = tf(numerator,denominator,'ts',1, 'Variable','z^-1')
producing:
tf_si =
0.9614 z^-1
----------------------------
1 - 1.663 z^-1 + 0.8313 z^-2
Sample time: 1 seconds
Discrete-time transfer function.
All the relevant vector elements need to be specified.

More Answers (0)

Products


Release

R2019b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!