Motor noise can be divided into three categories: aerodynamic, mechanical, and electromagnetic noise sources. In recent years, people have paid more and more attention to the impact of electromagnetic noise sources. This is mainly due to two reasons:
(a) For small and medium-sized motors, especially those rated below 1.5kW, electromagnetic noise dominates the acoustic field.
(b) This type of noise is primarily due to the difficulty in changing the magnetic properties of the motor once it is manufactured.
In previous studies, the influence of various factors on motor noise has been widely explored, such as the effect of pulse width modulation current on the acoustic noise behavior of internal permanent magnet synchronous motor drives; the influence of windings, machine frames and impregnation on the stator resonant frequency; the influence of core clamping pressure, windings, wedges, tooth profiles, temperature, etc. on the vibration behavior of stators of different types of motors.
However, the impact of stator core laminations on motor vibration behavior has not been fully investigated, even though clamping of the laminations is known to increase core stiffness and, in some cases, may even act as a vibration damper. Most studies model the stator core as a thick, uniform cylindrical core to reduce modeling complexity and computational burden.
Researchers at McGill University and their team analyzed a large number of motor samples to investigate the effects of laminated and non-laminated stator cores on motor noise. They created CAD models based on the measured geometry and material properties of actual motors, using a 4-pole, 12-slot interior permanent magnet synchronous motor (IPMSM) as a reference model. The laminated stator core was modeled using the Laminated Model Toolbox in Simcenter 3D, which sets parameters according to the manufacturer's specifications, including damping coefficient, lamination method, interlayer tolerance, and shear and normal stress of the adhesive. To accurately assess the acoustic noise emitted by the motor, they developed an efficient acoustic model that allows for coupling between the stator and the fluid, modeling the acoustic fluid surrounding the existing stator structure and analyzing the acoustic field around the IPM motor.
Figure 1. (a) Two-dimensional electromagnetic model. (b) Variation range of design variables in the entire design space.
The researchers observed that the vibration modes of the laminated stator core have lower resonant frequencies than the non-laminated stator core of the same motor geometry; despite frequent resonances during operation, the sound pressure level of the laminated stator core motor design was lower than expected; the correlation coefficient value exceeding 0.9 indicates that by relying on a surrogate model to accurately estimate the sound pressure level of the equivalent solid stator core, the computational cost of modeling laminated stators for acoustic studies can be reduced.
Figure 2 Sound pressure levels of laminated and non-laminated stator core samples of a 4-pole, 12-slot IPM motor
Figure 3 Spearman correlation coefficient distribution of laminated and non-laminated stators from 500 RPM to 3000 RPM