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Obtain Transfer Function for Bode Plot data from PLECS Software

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normal_user
normal_user el 21 de Jun. de 2024
Comentada: Mathieu NOE el 20 de Ag. de 2024
I have some bode plot data in an excel sheet which contains following columns.
Frequency / Hz Am1:Measured current Am1:Measured current
I have a range of values under each of this columns, I am interested in finding the transfer function that can generate similar bode plot.
Is this possible? If yes, how can I achieve it using MATLAB?
Attaching the CSV and the original bode plot here. Bode plot was generated using PLECS software.

Respuestas (1)

Mathieu NOE
Mathieu NOE el 25 de Jun. de 2024
hello
If you have the signal processing toolbox, you can use invfreqs or invfreqz to identify a transfer function
here I used invfreqs to generate a continuous time model (transfer function) , that I then converted to dicrete model (fyi)
you can try to adapt the numerator and denominator order to find the best match (with minimal order)
NB that your data are a bit coarse , frequency resolution is not great , especially to have a good estimate of the poles damping / frequency
data = readmatrix('plecsbode_og.csv');
freq = data(:,1);
mod_dB = data(:,2);
phas_deg = data(:,3);
Mag = 10.^(mod_dB/20); % convert dB to linear magnitude
Response = Mag.*exp(1j*pi/180*phas_deg); % Complex Vector
Ts = 0.5/(2*(max(freq)));
Fs = 1/Ts;
% TF design
NA = 6;
NB = NA-2;
W = 2*pi*freq;
[num,den] = invfreqs(Response,W,NB,NA,[],100);
hverif = freqs(num,den,W);
% convert to SS
[A,B,C,D]=tf2ss(num,den);
[Ad,Bd,Cd,Dd] = c2dm(A,B,C,D,Ts,'matched');
SYS = ss(Ad,Bd,Cd,Dd,Ts);
[M,P] = bode(SYS,W);
M = squeeze(M);
P = squeeze(P);
P = wrapTo180(P);
figure(1)
subplot(2,1,1),semilogx(freq,20*log10(Mag),'b',freq,20*log10(abs(hverif)),'r',freq,20*log10(M),'c');
legend('data','TF ','SS ');
xlabel('Frequency (Hz)');
ylabel('modulus (dB)');
subplot(2,1,2),semilogx(freq,wrapTo180(phas_deg),'b',freq,180/pi*(angle(hverif)),'r',freq,(P),'c');
legend('data','TF ','SS ');
xlabel('Frequency (Hz)');
ylabel('modulus (dB)');

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