Analysis of the electromagnetic acoustic noise and vibrations of a … · 2018-06-23 · Essential...

Essential Engineering Intelligence

Analysis of the electromagnetic acoustic noise and vibrations of a high-speed brushless DC motor

J. Le Besnerais, Q. Souron, E. DevillersEOMYS ENGINEERING, www.eomys.com

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A. Introduction

Square-wave-driven BLDC motor

Surface PM, p=2 pole pairs

Concentrated tooth winding, Zs=12 stator slots

Very noisy!

Objectives: theoretical, numerical and experimental analysis of vibro-

acoustic behaviour at no-load

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B. Theoretical analysis: mechanical vibrations

Bearing imperfections create vibrations proportional to rotational frequency fr

Irregularities of the ball cages create vibrations at 0.36 fr

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B. Theoretical analysis: magnetic vibrations

Maxwell forces apply to both stator and rotor, they are proportional to airgap flux density squared

Flux decomposition in permeance / magnetomotive force for harmonic analysis: wave of frequency f and wavenumber r noted (r,f)

Lowest positive wavenumber: r=GCD(Zs,2p)=4 at multiple of 2fs

Pulsating radial & tangential (cogging) forces: r=0 at multiples of LCM(Zs,2p)fR

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B. Theoretical analysis: magnetic vibrations

Highest force has a wavenumber r=2p=4

Due to high speed operation this force wave can

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C. Numerical analysis: introduction

MANATEE® electromagnetic & vibro-acoustic software

Use of fast & accurate subdomain models for electromagnetics

Simulation are carried up to 20 kHz in a few seconds

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C. Numerical analysis: ideal case

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Stator elliptical mode (2,0) found at 8 kHz

Rotor first bending mode (1,0) found at 2 kHz

Main radial force and vibration occurs at r=4 f=2fs

Radial force spectrogram and radial vibration spectrograms:


C. Numerical analysis: ideal case

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The spectrum is less rich than the experimental one

There is no strong resonance contrary to experiments, and no excitation of the elliptical mode (2,0)

The ideal case is not realistic: eccentricities, pole displacement must be included


C. Numerical analysis: 10% dynamic eccentricities

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C. Numerical analysis: rotor vibration due to cage defaults

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C. Numerical analysis: rotor pole displacements

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C. Numerical analysis: all imperfections

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D. Experimental analysis

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Run-up with microphones & accelerometers

« Spatiogram technique »: the radial vibration waves are filtered according to their wavenumber to identify both frequencies f and wavenumbers r

8 accelerometers are used -> up to r=4 can be identified (Shannon)



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Rich vibration spectrum with sidebands at 0.37 fr

Resonance with mode 1 identifed as rotor bending mode with ODS at 2 kHz

Resonance with mode 2 identifed as stator elliptical mode with ODS at 8 kHz



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r=1 r=2

Mode 1

Spatiograms confirm theoretical & numerical results

Strong presence of wavenumber 1 is due to assymetrical pole placement and dynamic eccentricities



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r=4

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E. Conclusions

MANATEE® software allows to quickly identify the vibroacoustic impact of imperfections in terms of frequencies and wavenumbers

Spatiogram experimental technique allows characterizing the vibration waves responsible for noise in terms of frequency, wavenumber and rotation direction

Studied BLDC is noisy due to uneven pole spacing and dynamic eccentricity

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Thank your for your attention, any questions ?

EOMYS ENGINEERING www.eomys.com

Analysis of the electromagnetic acoustic noise and vibrations of a … · 2018-06-23 · Essential...

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