Overview
Closeup |
For motors, reducing vibration and noise is a critical issue.
Cogging torque is a major cause of vibration and noise.
The cogging torque in an SPM motor is strongly affected by the magnet.
One solution to reduce the cogging torque is to use a step-skewed magnet.
This note presents the use of magnetic field analysis to evaluate the cogging
torque of an SPM motor with a step-skewed magnet. |
Flux Density Distribution
Fig. 1 shows the flux density distribution at the rotation angle of 60
degrees. Fig. 2 shows the graph for the frequency analysis of the flux
density waveform in the gap. The upper limit of the frequency component
is 1440 Hz.
As shown in Fig. 1, the magnetic circuit is changed by the application
of the step skew. As shown in Fig. 2, the ratio of the frequency component
at 360 Hz, which is the fundamental frequency of the cogging torque, is
13% when the motor has no step skew and 8% with the step skew. So it is
expected that the cogging torque may be reduced by applying the step skew. |
Closeup |
Closeup |
Cogging Torque
Closeup |
Fig. 3 shows the cogging torque waveforms of the SPM motor with and without
a step skewed magnet. When the magnet is step skewed, the peak value of
the cogging torque is reduced by about 50 percent. |
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