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

AuthorsJean Le Besnerais ; Quentin Souron ; Emile Devillers
StatusPublished in: PEMD 2016
Date19-21 April 2016
Keywordsmagnetic forces, vibration, acoustic noise, BLDC, PMSM, high-speed


In this paper, the acoustic noise and vibrations due to Maxwell forces of a 4-pole, 12-slot, high-speed brushless DC motor (BLDC) is analysed up to 90 kRPM. The harmonic magnetic forces present in the machine are first analytically characterized, and validated with numerical simulations using MANATEE electromagnetic and vibro-acoustic software. The effects of rotor vibrations due to bearing faults, pole displacements and eccentricities are considered. Finally, some complete experimental measurements relying on “spatiogram” techniques are run to characterize the vibration waves (wavenumber and frequency) involved in acoustic noise generation. These results are compared to simulations and it is demonstrated that the observed high acoustic noise is due to machine imperfections creating harmonic forces exciting the bending mode of the shaft and the stator elliptical mode.

Preprint and full paper

The preprint can be accessed here: The full paper can be accessed on IET website.The presentation made at PEMD conference can be accessed here:


A main challenge of high-speed electrical machines is their vibroacoustic design: when increasing the supply frequency, the largest magnetic forces at twice the electrical frequency can hit structural modes of the stator and rotor. This 2f excitation is generally negligible in “low-speed’ machines because it has a frequency at which the human’s ear is not very sensitive, and a wavenumber r=2p which is too high to create significant radial deflections of the stator core due to its increased stiffness.MANATEE software is an efficient design tool to account for noise and vibration during early electromagnetic design loops of high speed electric machines.

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