Signal processing with high harmonic content... Fourier... Filter???

10 Mar 2011
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Hi, I have a voltage (v) and current (i) signals with high harmonic content. Also these signals are generated by a variable frequency generator. For this reason, I don't have the fundamental frequency. ...-I want to calculate active and reactive power using v and i-... I know that simulink has several blocks to do that (some of them using Fourier), but it is necessary the fundamental frequency. Thanks,

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Indira
Indira on 10 Mar 2011
I have identified from the frequency spectrum (voltage) three important frequencies (329.5 Hz, 554.9 Hz and 1110 Hz) which have almost all the energy. It doesn't seem to be harmonics because they are not an integer from a fundamental frequency.
What can I do?... CAN I USE A FILTER AND THEN CAN I CALCULATE THE ACTIVE AND REACTIVE POWER??

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 Accepted Answer

Walter Roberson
Walter Roberson on 10 Mar 2011

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What resolution are you using for your frequency?
554.9 is, to within round off error, half of 1110.
329.5 is roughly 1110/3 (=370). 330 is 1/3 of 1100 for example.
Let us suppose, then, that the fundamental was fairly close to 330, then about 550 would be 3/2 times larger and 1110 would be 2 times larger.

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Walter Roberson
Walter Roberson on 11 Mar 2011
I messed up the ratios. 5/3, not 3/2, and 10/3 not 2. That would suggest a fundamental of about 110, with 330 being 3 times larger, 550 being 5 times larger, and 1100 being 10 times larger.
Indira
Indira on 11 Mar 2011
These signals were acquired with 3000 samples/second.
Your answer seems to be reasonable, but according to the frequency spectrum these frequencies are 3 of the 6 important frequencies I can see.
What's your view?
Walter Roberson
Walter Roberson on 11 Mar 2011
Where do the other 3 important frequencies show up?
Indira
Indira on 11 Mar 2011
The firs number is the frequency and the second one is the amplitud:
1)(179.8,43.88), 2)(329.5,107.3), 3)(450.8,68.84), 4)(554.9,426.1), 5)(1110,235.1) and 6)(1335,78.1)
Indira
Indira on 11 Mar 2011
I think I need a filter in the frequency domain... then try to calculate active power by each frequency...
Walter Roberson
Walter Roberson on 11 Mar 2011
Sorry, I poked around with those frequencies, but nothing came to mind.

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