Acoustic noise of electromagnetic origin in an ideal frequency-converter-driven induction motor

With the advent of power electronics, there has been increasing demand for variable-speed drives in industrial applications because significant energy savings can be achieved. However, the use of frequency converters in driving induction motors has resulted in significant increase in acoustic-noise radiation. While there have been numerous studies on the acoustic-noise-generation mechanisms in variable-speed drives, the problem remains unsolved. The increase in acoustic-noise radiation in inverter-fed induction motors has been mainly attributed to the time harmonics introduced by the converters. A general algorithm is presented to compute the change in sound-power level of a variable-speed induction motor due to the change in the speed of operation in the absence of time harmonics (i.e. driven by an ideal frequency converter). General qualitative results based on this algorithm indicate that, even if an ideal converter can be designed to eliminate all the time harmonics, the acoustic-noise radiation of electromagnetic origin can still be significantly increased by the change in speed. This algorithm can therefore be used to help establishing the lowest limit of acoustic-noise radiation which can ever be achieved independent of frequency-converter configurations for a variable-speed induction motor