Acoustic noise reduction for an inverter-fed three-phase induction motor

Acoustic noise produced by electrical machines is not only a nuisance to the listener, but can also pose a significant health risk to humans. In the workplace in particular, acoustic noise emitted from electric motors has become a recognized health hazard, especially for persons who are exposed to noisy environments for long periods of time. In many applications, induction motors are driven from variable speed drive systems, and both the change in supply frequency, and time harmonics introduced by the inverter switching processes, can contribute to increased motor vibration and acoustic noise. While much research has been conducted on acoustic noise and vibration reduction introduced by inverter switching harmonics, considerably less work been done on the reduction of sound power radiated at frequencies close to the fundamental drive frequency and its low-order multiples. This paper describes a new approach to reduce the sound power level of electromagnetically induced induction motor acoustic noise, which dynamically adjusts the operating frequency of the supply inverter to avoid resonant noise peaks, while maintaining constant motor torque/speed operating conditions by simultaneously adjusting the V/f ratio. Experimental results confirming the concept are included for a range of operating conditions for a test case motor.