Mechanical slot modulation effect, also called tooth sampling effect, refers to the fact that airgap magnetic stress waves are “sampled” when converted to physical magnetic forces applied to stator teeth. Consequently, due to Shannon theorem, the maximum stress wavenumber seen by the stator yoke is given by Zs/2 (half the number stator slots).
Application to e-NVH
This example illustrates in a 12 stator slots and 10 poles Permanent Magnet Synchronous Machines (PMSM) the sampling effect of the fundamental stress wave (r=2p=10) in an equivalent stress wave of wavenumber r=-2:
In EV HEV NVH applications, for instance in a Zs=48 stator slots p=4 pole pairs PMSM, Maxwell stress waves of wavenumber r=11p+p=13p-p=12p=48 (interaction of 11p/13p rotor field harmonic with fundamental field) are experienced as pulsating forces.
Application to MANATEE
MANATEE software specialized in the e-NVH simulation of electrical machines and noise reduction of electric motors includes slot modulation effects.