Electrical – Are ripples and harmonics the same thing

harmonicsripple

I started working on the "Direct Power Control of Grid Connected Voltage Source Converters", everywhere in the literature, authors state that one of the major drawbacks of this control technique is the presence of active and reactive power ripples due to the use of Hysteresis controllers.

In the other hand I've already worked on Power Harmonics, active power filtering and UPQCs, and i know that harmonics must be multiple of the fundamental frequency.

My questions are the following :

  • Are "power ripples" cause by hysteresis controllers considered "harmonics"?
  • What are the frequencies of those power ripples?
  • Do they affect the value of THD?

Best Answer

Are "power ripples" cause by hysteresis controllers considered "harmonics" ?

No, not all of them, harmonics are specific frequencies that are resonant, all noise ripples such as switching noise or hysteresis add up to the total noise 'ripple' of the circuit. Ripple is less applicable in AC systems because the signal (the AC waveform itself) is much higher than the noise. To see the noise in an AC system you need to look at the frequency content or subtract out the first harmonic (ie 60 or 50Hz)

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Source: http://www.compliance-club.com/archive/keitharmstrong/design_techniques6.html

What are the frequencies of those power [harmonics]?

Typically multiples of the carrier, if your on 60Hz, you get one at double and triple so 120Hz and 180Hz and so on.

Do they affect the value of THD ?

THD only takes into consideration the harmonics to the fundamental:

$$ %THD = \frac{\sqrt{v_2^2+v_3^2 \ddots v_n^2}}{v_1^2} $$