Overview
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Motors are not only required to be more compact and have higher efficiency,
but also to have less noise and vibration. One of the reasons of noise
and vibration is cogging torque, which is caused by the interaction between
the iron core and the permanent magnet. Cogging torque can be reduced by
applying skew.
This note presents the use of magnetic field analysis to evaluate the magnetic
flux density distribution and cogging torque of an SPM motor with a skewed
magnet. |
Magnetic Flux Density Distribution
| Figure 1 shows the magnetic flux density distribution at the rotation angle
of 90 degrees. The magnetic circuit is seen to be changed by skewing the
magnet. This change seems to have an effect on the cogging torque waveform. |
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Cogging Torque Waveform
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Figure 2 shows the cogging torque waveforms when the skew angles are 0
degree and 30 degrees. When the magnet is skewed, the peak value of the
cogging torque is reduced by about 90 percent. |
Induced Voltage Waveform
Figure 3 shows the induced voltage waveform of the U-phase when the skew angles are 0 degree and 30 degrees. And Figure 4 shows the frequency component of the induced voltage waveform of the U-phase.
The high frequency component is reduced when the magnet is skewed. The ratio of the 60 Hz component, which is the basic frequency of all frequency components, is 71 percent when the skew angle is 0 degree, and the ratio is 82 percent when the skew angle is 30 degrees. Therefore, the induced voltage waveform is smoother for the skew angle of 30 degrees than that of 0 degree. |
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