The Total Harmonic Distortion component determines the total harmonic distortion (THD) over the given period $\frac{1}{f}$.

Consider that the input $u$ consists of harmonic RMS components $U_1$, $U_2\>$, $U_3$, etc. The total RMS component is then determined by:

The calculation of the total harmonic distortion is based on the parameter $\mathrm{useFirstHarmonic}$. The default value $\mathrm{useFirstHarmonic}\=\mathrm{true}$ represents the standard THD calculation used in electrical engineering http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=551-20-13 . The non-default value $\mathrm{useFirstHarmonic}\=\mathrm{false}$ calculates the THD typically used for the assessment of audio signals. If $\mathrm{useFirstHarmonic}\=\mathrm{true}$, the total higher harmonic content (harmonic order numbers > 1) refers to the RMS value of the fundamental wave:

If $\mathrm{useFirstHarmonic}\=\mathrm{false}$, the total higher harmonic content (harmonic order numbers > 1) refers to the total RMS:

In case of a zero input signal or within the first period of calculation, the boolean output signal $\mathrm{valid}$ becomes $\mathrm{false}$ to indicate that the calculation result is not valid. Valid calculations are indicated by $\mathrm{valid}\=\mathrm{true}$.

The component described in this topic is from the Modelica Standard Library. To view the original documentation, which includes author and copyright information, click here.