Audible noise level of motors used with AC drives


Thread Starter

Mark Sevelis

Does anyone have info about noise levels of motors being used with AC drives? Specifically, at 60 Hz and PWM Carrier frequencies at 2k, 4k, 6k, and 8k Hz. There seems to be very little info available on this subject. Doesn't matter who manufactures the motor: Baldor, Marathon,
U.S., SEW.

Mark Sevelis
please send to: [email protected]

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The audible noise levels have to do with several different factors.

First, the 60Hz portion of the drive is on the converter side and make no real difference that I know of on the motor side. The current / voltage waveforms induced in the motor cause the noise and these are typically generated from a PWM synthesized sine wave using a 700VDC bus.

The current loop design and PWM generation method determines how stable the current wave form is and is also related to whether or not the drive
is running with open loop field control or closed loop field control. Slip gain also plays a part in this. You can have two identical drives
running two identical motors each tuned a little different with large differences in audible noise. Once you become accustomed to this you
can actually tell by sound when a motor has too much current pouring through it.

Another factor is the motor design itself. Laminations ring at different frequencies and it is possible to excite different motors at
different switching frequencies.

Typically, the higher the switching frequency and better field control (closed loop flux vector) with a frequency compensated PWM modulation
algorithm will yield the closest thing to a perfect sinusoidal current waveform . . . hence the quietest motor.

Doubt if this was the definitive answer you were looking for . . . but what the heck it didn't cost you anything.

Ken Brown
Applied Motion Systems, Inc.