Need Help with FFT Analysis and Power Factor Calculation in MATLAB

Hello everyone,

I have a CSV file with two columns: "t" (time) and "i(t)" (current). I want to perform Fast Fourier Transform (FFT) analysis on the "i(t)" data to calculate the Total Harmonic Distortion (THD) and obtain information about power factor components, including displacement power factor and distortion power factor.

Here's what I need assistance with:

1. How can I read the CSV data in MATLAB with the "t" and "i(t)" column headers?

2. Calculate the FFT of the "i(t)" current data.

3. Determine the fundamental frequency and compute THD for the current signal.

4. Calculate the Displacement Power Factor (DPF) and Distortion Power Factor (DPFd).

I would appreciate any guidance or code snippets to help me achieve this analysis in MATLAB. Thank you in advance for your help!

Best regards.

Answer 1

[Chunru]

Here is the work flow:

1.Read the CSV data in MATLAB with the "t" and "i(t)" column header as a table

x = readtable("https://www.mathworks.com/matlabcentral/answers/uploaded_files/1537480/data.csv", "VariableNamingRule", "preserve")

x = 2048×2 table
       t          i(t)  
    ________    ________

       8e-06    0.044922
     1.6e-05    0.050391
     2.4e-05    0.050391
     3.2e-05    0.050781
       4e-05    0.050781
     4.8e-05    0.053906
     5.6e-05    0.053906
     6.4e-05    0.041016
     7.2e-05    0.041016
       8e-05    0.046875
     8.8e-05    0.046875
     9.6e-05    0.080078
    0.000104    0.080078
    0.000112     0.10938
     0.00012     0.10938
    0.000128     0.13867

2. Calculate the FFT

Plot the data

figure
plot(x.t, x.("i(t)"))

Since your data is not uniformly sampled, we need an interpolation

ts = diff(x.t(1:2));      % sampling time based on 1st two points (adjust this if necessary)
t = x.t(1):ts:x.t(end);     % uniform time points

t0 = x.t;
y0 = x.("i(t)");

% t0 need to be unique
[tu, ia] = unique(t0);
yu = y0(ia);

y = interp1(tu, yu, t);    % interplate the data
hold on
plot(t, y);
legend("original", "interp")

3. Determine the fundamental frequency and compute THD for the current signal.

p = 20*log10(abs(fft(y)));      % log scale in dB
figure
f  = (0:length(p)-1)/ts; 
plot(f, p);
xlim(f([1 50]));   % zoom in first 0 50 bins
% find the peak
[pmax, imax] = max(p);
hold on
plot(f(imax), p(imax), 'r*')

% Harmonic freq
f(imax)

ans = 125000

4. Calculate the Displacement Power Factor (DPF) and Distortion Power Factor (DPFd).

Try out the rest with the definition of THD, DPF and DPFd