Harmonics

Discussion in 'The Projects Forum' started by Cerkit, Aug 16, 2015.

  1. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
    275
    3
    Hi All. I have asked this question before but didn't really understand. It is regarding harmonics. I guess I am trying to have a visual understanding of what is going on in a circuit where harmonics are bieng generated. From an abstract perspective I understand that any distortion to a sine wave will result in a waveform that mathematically is proven to contain a fundamental and various multiples of that frequency.
    What does that look like in terms of the electrons in a cable, I can understand them oscillating back and forth 50 times per second, but when they suddenly get stopped (by a switching circuit thyristor etc), how do these harmonics get generated, I suppose I can't translate what multiple what the harmonics look like in practical terms in a cable.

    Thanks
     
  2. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
    275
    3
    Also maybe it is because I don't understand how some electrons are made to move at a different frequency to other electrons independently and how they manage to do that, rather than all just moving back and forward at the same time.
     
  3. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    If you have asked this question before, perhaps you just didn't like the answer. How about a change of perspective?

    You look at a waveform and ask, what harmonics does this generate. Change of perspective: What spectrum of harmonics produces this waveform. Spectrum and waveform are different sides of the same coin. They represent the same energy interpreted from different view points, energy verses time and, energy verses spectrum. One translates to the other.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,539
    1,251
    If you search for fourier analysis, fourier square wave, fourier triangle wave, fourier harmonics, etc., you will find many excellent explanantions of how harmonics affect the overall waveform, along with java applets that let you adjust the harmonics to see the results.

    It is not the case that for a complex wave, there are some electrons moving at each of the harmonic frequencies. Everyone moves as the composit waveform dictates.

    ak
     
    Last edited: Aug 17, 2015
  5. crutschow

    Expert

    Mar 14, 2008
    13,014
    3,234
    In the time domain, the electrons don't move at separate frequencies, they all move together at any instant in time as AK noted, to the sum of the fundamental plus the harmonics.
    It's only in the frequency domain that you see the individual harmonics.
    If you don't understand the difference between the frequency domain and the time domain, you need to look that up.
     
  6. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
    275
    3
    Thank you for all the explanations. I realize my error was in trying to visualise the frequency domain in terms of electrons and movement when in reality the spectrum is determined via mathematical tools and transformations between time and frequency domain and therefore is illogical to try and think it as different electrons at different frequencies, they all move together according to the superposition of the different waveforms in the spectrum.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,539
    1,251
    By George, I think he's got it.

    ak
     
Loading...