This tutorial on magnetic noise control techniques of electric machines was presented at the International Conference on Electrical Machines in Valencia, 5th September 2022 by J. Le Besnerais. The tutorial first recalls the causal chain of magnetic noise generation, from electromagnetic field to sound pressure field, focusing on acoustic noise due to stator yoke vibrations in Permanent Magnet Synchronous Machines. The main noise control techniques focusing on magnetic circuit dimensions are then reviewed: slot/pole combination, winding design, pole shaping, skewing (V-shape, linear), slot opening and stator / rotor notching. For each technique, the theoretical optimal design values are provided when possible, and a numerical simulation with Manatee e-NVH software is run to illustrate the effect of the design variations on magnetic noise, average electromagnetic torque and torque ripple. Open circuit and full load variable speed results are presented. Examples are applied on a 48s8p IPMSM used for automotive traction application. The different techniques are finally ranked according to their influence on magnetic noise, showing 5 to 30 dB influence on the acoustic noise level of the electrical machine depending on the technique. The presentation is focused on e-machine noise mitigation techniques from the electromagnetic design point of view (magnetic circuit dimensions). It does not consider additional techniques that can be used at control level such as current angle, harmonic current injection, switching strategy and switching frequency.

In this paper, a passive method for the noise reduction of the PMSM (Permanent Magnet Synchronous Machine) is presented. The principle is to add an auxiliary three-phase winding into the same slots as the initial stator winding, short-circuited via three capacitors of suitable values. The aim is to create a damping effect for flux density harmonic components, especially high-frequency harmonics from the PWM (PulseWidth Modulation), in the air gap in order to reduce the noise and vibration of the PMSM. The method can significantly reduce the global sound pressure level and vibrations for specific frequencies. Because of passive features, the additional winding effectively mitigates magnetic noise without greatly increasing the complexity of design and manufacturing, which also extends its applicability to different PMSMs.

Acoustic noise sources in Hybrid Electric Vehicles or full Electric Vehicles (HEV/EV) must be controlled to guarantee an adequate level of acoustic comfort to both passers-by, drivers, and passengers. This article focuses on switching noise resulting from power electronics, also called Pulse Width Modulation (PWM) noise, which may be responsible for unpleasant sounds in Electric Drive Units (EDU). The physics of PWM generation principle is first reminded, from voltage to magnetic excitation harmonics, and noise radiation. An original testbench setup to automatically evaluate the impact of the choice of commutation scheme (e.g., SPWM, SVPWM and DPWM) and frequency is described. Finally, a corpus of motor noise recordings with various PWM strategies is analyzed by means of sound quality metrics and the results are interpreted.