How can I estimate transfer function from frequency data?
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Hello, I have magnitude and phase data of a system in frequency domain:
I want to derive its transfer fuction with the following code:
load('Magnitude.mat');
load('Phase.mat');
load('freq.mat');
data = frd(Magnitude.*exp(1j*Phase*pi/180),freq); % Frequency-response data model
np = 6; % # of poles
nz = 6; % # of zeros
iodelay = NaN;
sys = tfest(data,np,nz,iodelay);
bodeplot(sys,{2*pi*1e0,2*pi*1e6})
sys.Report.Fit
h1 = gcr;
setoptions(h1,'FreqUnits','Hz')
setoptions(h1,'MagUnits','abs')
Here is the result:
The estimated TF does not fit well with the phase angle but fit percent report is 98% and MSE is very high (3.6e6). I tried it for any number of zeros and poles but I got even worse results.
Could you please help me to solve it?
Thanks
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Respuestas (1)
Star Strider
el 13 de Mayo de 2022
Editada: Star Strider
el 13 de Mayo de 2022
Change (increase) ‘np’ using only the number of poles (initially use the default value for the number of zeros and if necessary, fine-tune later with ‘nz’) until you get an appropriate fit.
EDIT — (13 May 2022 at 14:50)
Increase the system order. I was able to get an acceptable fit to both the magnitude and phase with:
ord = 22;
sys = ssest(data,ord);
Also:
figure
compare(data,sys)
% sys.Report.Fit
h1 = gcr;
setoptions(h1,'FreqUnits','Hz')
setoptions(h1,'MagUnits','abs')
.
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