Technically "Interharmonics"are voltages or currents with a frequency that is a non-integral multiple of the fundamental supply frequency, while each harmonic frequency is an integral multiple of the supply frequency.
Interharmonics,always present in the power system, have recently become of more importance since the widespread use of power electronic systems results in an increase of their magnitude. Interharmonics are caused by the asynchronous switching of semiconductor devices in static converters such as cyclo converters and pulse width modulation(PWM) converters, or by rapid changes of current in loads operating in a transient state.
Practically "Interharmonics" are explained as Electronics and communications devices in the smart grid can increase a rare, and not well-understood, distortion.
Using sophisticated power electronics and communications systems to improve power system efficiency, flexibility and reliability is increasing interharmonic distortion and putting new equipment sensitive to that distortion on the system. Understanding interharmonics is necessary to prevent them from adversely affecting system operation.
IEEE Standard 519-2014, Recommended Practice and Requirements for Harmonic Control in Electric Power Systems, defines interharmonics as any “frequency component of a periodic quantity that is not an integer multiple of the frequency at which the supply system is operating.” IEC 61000-2-1 includes a similar definition. Mathematically, with f the supply (fundamental) frequency and m any positive non-integer, any signal with the frequency mf is an interharmonic of f. This is similar to the harmonic definition, nf, where f once again represents the fundamental frequency, but n represents any integer greater than zero.
While interharmonic and harmonic definitions are similar, their difference that harmonics are periodic at the fundamental frequency and interharmonics are not is important. All periodic waveforms can be represented by their fundamental component and a Fourier series of harmonics with various magnitudes, frequencies and angles. Interharmonics are not periodic at the fundamental frequency, so any waveform containing interharmonics is non-periodic and any non-periodic waveform includes interharmonics. The level of interharmonic distortion can be thought of as a measure of a waveform’s non-periodicity.
We will See the sources of interhormonics in next article soon,
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