Why is my fundamental frequency at the 15th harmonic order

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Jmv
Jmv 2020-5-4
评论： Rena Berman 2020-5-14
Dear Matlab Community.
I am trying to implement a code to show harmonic content and order in Matlab. my fundamental is supposed to be at harmonic order 1, however the ouput plot I am getting is wrong and I am having difficulies proceeding.
I would really apreciate any help. Thanks
[D,S,R] = xlsread('test data.xls');
v = D(:,2);
Signal = D(:,2);
Ts = 0.00005; % Sampling Interval (seconds)
Fs = 1/Ts; % Sampling Frequency (Hz)
Fn = Fs/2;
%PERFOM FFT
N = length(Signal);
meanSignal = mean(Signal); % ‘Signal’ Mean
FTSignal = fft(Signal-meanSignal)/N;
Fv = linspace(0, 1, fix(numel(FTSignal)/2)+1)*Fn; % Frequency Vector
Iv = 1:numel(Fv); % Index Vector
%Plotting Harmonics (THD)
har_mag = abs(FTSignal(Iv))*2;
figure;
bar(har_mag(1:20),0.4)
xlabel('Harmonic Order','fontsize',10);
ylabel('Voltage (V)','fontsize',10)
hold off
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Rik
Rik 2020-5-5
Why did you edit away important parts of your question and delete several comments? That is extremely rude.

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采纳的回答

Star Strider
Star Strider 2020-5-4
I am not certain what you are doing, or what result you want.
One problem is that you also need to specify the x-values of the bars in your bar call:
bar(Fv(1:20), har_mag(1:20),0.4)
If you want to find all the relevant peaks and their frequencies, add these lines after your existing (posted) code:
[pks,locs] = findpeaks(har_mag, 'MinPeakProminence',0.5);
FreqPeaks = table(Fv(locs)', pks, 20*log10(pks), 'VariableNames',{'Freq', 'Amp', 'dB'})
figure
plot(Fv, 20*log10(har_mag))
hold on
plot(Fv(locs), 20*log10(har_mag(locs)), '+r')
hold off
grid
axis([0 1200 -15 60])
The ‘FreqPeaks’ table has all the identified peaks (linear and dB) and their associated frequencies.
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Star Strider
Star Strider 2020-5-4
As always, my pleasure!
The ‘FreqPeaks’ table changes again so the fourth column is now the percentage of the fundamental amplitude:
FreqPeaks = table(Fv(locs)', Fv(locs)'/Fv(locs(1))', pks, pks/pks(1)*100, 'VariableNames',{'Freq', 'HarmNr', 'Amp', 'PctFund'})
and the bar plot becomes:
figure
bar(FreqPeaks{:,2}, FreqPeaks{:,4})
xlabel('Harmonic Number')
ylabel('Percent of Fundamental Amplitude')
xlim([0 20])
Setting the y-scale to logarithmic makes them a bit easier to see:
figure
bar(FreqPeaks{:,2}, FreqPeaks{:,4})
set(gca, 'YScale','log')
xlabel('Harmonic Number')
ylabel('Percent of Fundamental Amplitude')
xlim([0 20])
Choose the one that works best in your application.
Star Strider
Star Strider 2020-5-4
As always, my pleasure!
I wasn’t initially certain what you want to do. I’m glad we got this sorted!

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更多回答（1 个）

Rafael Hernandez-Walls
why don't use the FTTSHIFT, this function Shift zero-frequency component to center of spectrum.

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