how to get the parameters of step response?
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hi everybody.. how can get 'num' and 'den' when i have the step response? i'm using matlab 2010. please help me.thank you.
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Ryan G
2012-11-27
You can use the system identification GUI to analyze data and estimate a transfer function from that data. In this case you are using step response data so the input would be the step and the output would be the response.
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Ryan G
2012-11-27
If you have a transfer function, say sys, you can obtain the num and den like this:
sys = tf(1,[1 1]); %demo transfer function
num = sys.num;
den = sys.den;
Rajiv Singh
2012-11-27
To elaborate on what Ryan wrote, suppose y is the vector of step response data and Ts is the sampling time.
N = length(y);
u = [zeros(10,1); ones(N,1)];
y2 = [zeros(10,1); y];
stepdata = iddata(y,u,Ts);
model = tfest(stepdata, numpoles, numzeros); % available >=R2012a
where numpoles and numzeros are the desired number of poles and zeros for the transfer function.
[num,den] = tfdata(model); % or, simply do model.num and model.den
The zero-padding of the data was done to ensure that the step transition (0 to 1) is evident in the data.
Rajiv
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Rajiv Singh
2012-11-27
[num,den] = tfdata(model), or, simply do model.num and model.den where model is the transfer function
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