FFT and Fourier series formulas from CSV data file
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Seweryn
on 31 Oct 2023
Commented: Walter Roberson
on 31 Oct 2023
Hi guys, I'm struggling with a problem. I obtained the rms values for ch1 (voltage) and ch2 (current) and performed an FFT analysis in simulink (as you can see in pdf file), but I wonder if I can get the Fourier series formulas for each waveform in Matlab? Values start at line 22 in .csv file (A22:C10021)
I would be delighted to any help.
Kind regards,
Seweryn
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Accepted Answer
Walter Roberson
on 31 Oct 2023
Moved: Walter Roberson
on 31 Oct 2023
filename = 'tek0005.csv';
data = readmatrix(filename, 'HeaderLines', 21);
time = data(:,1);
T = mean(diff(time));
Fs = 1./T;
L = height(time);
freqs = Fs/L*(0:L-1);
ch1 = data(:,2);
ch2 = data(:,3);
F1 = fft(ch1);
F2 = fft(ch2);
tiledlayout('flow');
nexttile();
plot(freqs, abs(F1)); title('ch1');
xlabel("f (Hz)"); ylabel("|fft(ch1)|")
nexttile();
plot(fftshift(abs(F1))); title('shifted ch1');
nexttile();
plot(freqs, abs(F2)); title('ch2');
xlabel("f (Hz)"); ylabel("|fft(ch2)|")
nexttile();
plot(fftshift(abs(F2))); title('shifted ch2');
2 Comments
Walter Roberson
on 31 Oct 2023
https://en.m.wikipedia.org/wiki/Euler%27s_formula
now consider exp(i*x + c) where c is real.
Each entry in the fft output is a complex number so using the equivalence you can separate into sin and cos components.
There will be thousands of these components unless you are willing to say that if abs() of a component is less than a tolerance then you want to consider the component to be effectively 0.
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