find fft of AC variable load in MATLAB

[nishat anjum khan]

Hi everybody..i am working with a project where i have to work with real time data...i am using variable ac load and via Arduino i plot real time voltage and current in matlab...then i take some samples at a time and do fft of it in MATLAB..we are working with 50Hz system but i can't found harmonic in 50Hz...what should i do to get it? i am attaching my code..please help someone...plzzz

 

[weetabixharry]

Your code is extremely badly formatted and difficult to read. There are numerous variables defined that are never used. There are numerous initial values that are never used. Indentation is all over the place.

That code can comfortably be reduced to under 20 lines. Please tidy it up so it is easier for anyone to help (and for you to understand).

In my opinion, your first few lines should be:

close all; clear all; clc;

% Open Serial COM Port
s = serial('COM1','Baudrate',57600);

The rest of your initialisation is unnecessary. I also think lines 44 - 86 can be removed.

I don't think you should be using tic and toc for timing. You have a known baud rate, so you should be using this to determine your sampling frequency, f_s. Then, in your N-sample FFT, you know the bin spacing is f_s/N.

From this, you will find the true frequency of any harmonic.

 

[nishat anjum khan]

thank u very much for your reply..i will rearrange my code...can u just tell me how can i determine sampling frequency from baud rate?

 

[weetabixharry]

thank u very much for your reply..i will rearrange my code...can u just tell me how can i determine sampling frequency from baud rate?

Assuming you are receiving a constant stream of data, the relationship is direct, so you can figure it out yourself. Here is a definition of Baud rate: [link] and here is a definition of sampling rate: [link].

If you do not have a constant stream of data (and, instead, the data arrives at irregular intervals), then the FFT cannot be used directly anyway. Hopefully, this is not the case.