Why is my fundamental frequency at the 15th harmonic order

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

[Stephen23]

Original question by Jmv, recovered from Google Cache (the uploaded files could not be recovered):

Why is my fundamental frequency at the 15th harmonic order

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

[Rik]

Why did you edit away important parts of your question and delete several comments? That is extremely rude.

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Star Strider]

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.

[Star Strider]

My pleasure.

I am still not certain what you want.

I added a column to ‘FreqPeaks’, and an associated bar plot:

[pks,locs] = findpeaks(har_mag, 'MinPeakProminence',0.35);
FreqPeaks = table(Fv(locs)', Fv(locs)'/Fv(locs(1))', pks, 20*log10(pks), 'VariableNames',{'Freq', 'HarmNr', '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])

figure
bar(FreqPeaks{:,2}, FreqPeaks{:,3})
xlabel('Harmonic Number')
ylabel('Ampl;itude')
xlim([0  20])

Is this closer?

[Star Strider]

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]

As always, my pleasure!

I wasn’t initially certain what you want to do. I’m glad we got this sorted!

Answer 2

[Rafael Hernandez-Walls]

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