Interharmonics in power systems

IEC-61000-2-1 defines interharmonic as follows: between the harmonics of the power frequency voltage and current, further frequencies can be observed which are not an integer of the fundamental. They can appear as discrete frequencies or as a wideband spectrum. Harmonics and interharmonics of a waveform can be defined in terms of its spectral components in the quasisteady state over a range of frequencies. The term sub-harmonic does not have any official definition but is simply a special case of interharmonic for frequency components less than the power system frequency. Use of the term subsynchronous frequency component is preferred, as it is more descriptive of the phenomena. This paper discusses the sources of interharmonics, chief among which is the cycloconverter. The impacts of interharmonics and the measurement of interharmonics are also discussed.