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 cycloconverters and pulse width modulation (PWM) converters, or by rapid changes of current in loads operating in a transient state.

This Application Note discusses the background, origin and measurement of interharmonics.

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