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

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.