The effect of magnet geometry on electric motor vibration

California Univ., Berkeley, CA
IEEE Transactions on Magnetics (Impact Factor: 1.42). 12/1991; DOI: 10.1109/20.278787
Source: IEEE Xplore

ABSTRACT A principal source of vibration in permanent magnet (PM) motors
and generators is the traveling forces on the stator induced by the
rotating permanent magnets. These forces are transmitted through the
stator and to the surrounding system. The magnetic forces were
calculated from the flux density by finite element methods (FEMs). The
dynamic reactions at the motor mounting points, which provide the
forcing function to the base system, were also calculated by FEMs. The
vibration characteristics and the transmissibility of each frequency
component were investigated using Fourier decomposition of the traveling
magnetic force. The results showed that for a radially centered rotor
the frequency components of the magnetic force were integer multiples of
the rotor speed multiplied by the number of magnetic poles. Higher
harmonics were more difficult to transmit, except when stator structure
resonance occurred. The edge shape of the PM determined the shape of the
magnetic force and the magnitude of the frequency components. By proper
shaping of the magnetic edges, the composition of the magnetic force
spectrum can be assigned to higher frequencies, reducing the overall
transmission to the base system

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