Total harmonic distortion

The total harmonic distortion (THD or THDi) is a measurement of the harmonic distortion present in a signal and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. Distortion factor, a closely related term, is sometimes used as a synonym.

In audio systems, lower distortion means that the components in a loudspeaker, amplifier or microphone or other equipment produce a more accurate reproduction of an audio recording.

In radio communications, devices with lower THD tend to produce less unintentional interference with other electronic devices. Since harmonic distortion can potentially widen the frequency spectrum of the output emissions from a device by adding signals at multiples of the input frequency, devices with high THD are less suitable in applications such as spectrum sharing and spectrum sensing.[1]

In power systems, lower THD implies lower peak currents, less heating, lower electromagnetic emissions, and less core loss in motors.[2] IEEE Standard 519-2022 covers the recommended practice and requirements for harmonic control in electric power systems.[3]

  1. ^ Blagouchine, Iaroslav V.; Moreau, Eric (September 2011). "Analytic Method for the Computation of the Total Harmonic Distortion by the Cauchy Method of Residues". IEEE Transactions on Communications. 59 (9): 2478–2491. doi:10.1109/TCOMM.2011.061511.100749.
  2. ^ "Total Harmonic Distortion and Effects in Electrical Power Systems – Associated Power Technologies" (PDF).
  3. ^ "IEEE Standard for Harmonic Control in Electric Power Systems". IEEE STD 519-2022 (Revision of IEEE STD 519-2014): 1–31. 2022. doi:10.1109/IEEESTD.2022.9848440. ISBN 978-1-5044-8727-6.