1. Definition

Fourier analysis is used to quantify the harmonic distortion of a signal. A periodic signal (voltage or current) of any form and frequency f ₀ is decomposed into a sum of sinusoidal signals, each of which has a frequency — called harmonic — which is an integer multiple of the fundamental frequency f ₀ . This multiple is called the harmonic rank. An example of this decomposition is shown in figure 1 . The amplitude of a harmonic component is generally expressed as a percentage of the corresponding fundamental quantity — this is the harmonic ratio.