Optimal Slot Numbers for Magnetic Noise Reduction in Variable-Speed Induction Motors

Abstract

Numerous empirical rules have been established in order to rightly choose the number of stator and rotor slots and limit the audible magnetic noise level radiated by induction machines. However, these rules never take into account the stator natural frequencies neither the fact that the motor is run at variable speed.In this article, a fast simulation tool of the variable-speed magnetic noise emitted by induction machines, based on fully analytical models, is presented. On the ground of these models, the analytical expression of main magnetic vibrations due to slotting reluctance harmonics are derived and experimentally validated, confirming the prime importance of slot combination in magnetic noise radiation.Some simulations are then run on a 700 W squirrel-cage motor in order to quantify the noise emitted by all possible combination of slot numbers in two and three pole pairs cases, including odd slot numbers. The obtained database efficiently replaces the old emperical rules on slot combination numbers and helps designing quiet induction motors. Similar database can be built for other power ranges.

Review of Switched Flux Wound-Field Machines Technology

“…SFWFMs with odd rotor pole numbers could lead to significant noise and vibrations due to unbalanced magnetic force which can be reduced by using Maxwell's stress tensor method [48,64].…”

Research on the radial electromagnetic force of inverter-fed induction machine with different slot combination using FEM

“…The distribution of axial magnetic field is approximately consistent,without considering the influence of end effect.Therefore 2-D half model can be used to analyse the transient magnetic field of the inverter-fed induction machine [5] [8] .And It's accurate to load volatge source considering the output voltage of inverter power supply is constant. Table V is the main parameters of inverter power supply [2] .…”

The Impact of the Rotor Slot Number on the Behaviour of the Induction Motor

“…The shape of the bars is chosen to belong to NEMA's class A design specification. The numbers are selected after a research with analytical equations and previously published works [17]. The created rotors are presented in Figure 2.…”