Laboratory for Dynamics of Machines and Structures 
Experimental research on structure-borne noise at pulse-width-modulation excitation
 J. Luznar, J. Slavič and M. Boltežar
Applied Acoustics, Volume 137, August 2018, Pages 33-39

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Abstract
Pulse-width modulation (PWM) is widely used in motor control and represents a carrier-frequency-dependent structural excitation. The PWM’s excitation harmonics are also reflected in an air gap’s electromagnetic forces, the transmitted bearing forces and the resulting structure–borne noise. Inappropriate carrier-frequency selection can cause additional electromagnetic noise. The latter can be reduced by a characterization of the coupling between the excitation harmonics and the structural dynamics. To obtain a clear insight into the physical phenomenon, an experiment with original motor parts is proposed, which introduces bearing force measurement and excludes the aerodynamic and mechanical sources of noise. The detailed dependence of the structure-borne noise on the PWM carrier frequency can be obtained by dense carrier-frequency measurements. The experimental results show that even at higher frequencies (above 10 kHz), the carrier-frequency selection can cause a 25 dB(A) difference in the total sound pressure level. The switching noise of PWM controlled machines can be reduced by the appropriate carrier-frequency selection in accordance with the structural dynamics.
Authors

Associate PhD student

Janez Luznar, PhD Student

  DOMEL, d.o.o.
  j.luznar@domel.com
  +386 1 4771 228

Associate Professor

Janko Slavič, PhD

  Ladisk, Faculty of Mechanical Engineering, University of Ljubljana
  janko.slavic@fs.uni-lj.si
  +386 1 4771 226
jankoslavic     jankoslavic    
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Professor

Miha Boltežar, PhD

  Ladisk, Faculty of Mechanical Engineering, University of Ljubljana
  miha.boltezar@fs.uni-lj.si
  +386 1 4771 608
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