Overview
Closeup
|
The induced voltage and surface flux density of the magnets can be measured
as a method to confirm the magnetization direction of the magnets to use
when developing a motor.
The surface flux density of the magnets is obtained using magnets with
radial and parallel anisotropic patterns by changing the decay angle from
0 degrees to 20 degrees and magnets with a polar anisotropy pattern by
changing the distance from the center pole from 8 mm to 17 mm. This note
presents the use of a magnetic field analysis to obtain and compare the
induced voltage and cogging torque of an SPM motor using these magnets.
|
Surface Magnetic Flux Density
|
|
The position the surface flux density distribution is measured is indicated
in Fig.1. The surface flux density of the magnets for the radial pattern,
parallel anisotropic pattern, and polar anisotropic pattern are indicated
in Fig.2, Fig.3, and Fig.4.
The waveform is closer to a sinusoidal waveform as the distance between
each magnetization direction, decay angle, and center pole increases, as
indicated in Fig.2, Fig.3, and Fig.4. Furthermore, there is a large difference
in the characteristics for the surface flux density of magnets with a radial
pattern, parallel anisotropic pattern, and polar anisotropic pattern. Therefore,
the magnetization pattern of the magnets can be confirmed by measuring
the magnetic flux density of the magnets. |
|
|
|
|
Induced Voltage and Cogging Torque
The induced voltage for the radial pattern, parallel anisotropic pattern,
and polar anisotropic pattern are indicated in Fig. 5, Fig. 6, and Fig.
7. The frequency components making up the induced voltage waveform for
the decay angle of 0 degrees and 8 mm distance from the center pole for
each magnetization direction is indicated in Fig. 8 (see Section 7, "Results
Display"). The frequency components making up the induced voltage
waveform for each distance from the decay angle and center pole are indicated
in Fig. 9, Fig. 10, and Fig. 11. The Cogging torque is indicated in Fig.
12, Fig. 13, and Fig. 14.
If the induced waveform for a decay angle of 0 degrees and an 8 mm distance
from the center pole for each magnetization direction indicated in Fig.
5, Fig. 6, and Fig. 7 is compared, the parallel anisotropic pattern is
the closest to a sinusoidal waveform followed by the radial pattern, and
then the polar anisotropic pattern. The ratio of harmonic components is
larger for the radial pattern and polar anisotropic pattern compared to
the parallel anisotropic pattern when comparing the frequency components
of the waveform indicated in Fig. 8. Therefore, the effects of the harmonic
components are larger for the parallel anisotropic pattern and polar anisotropic
pattern.
However, the induced voltage waveform is closer to a sinusoidal waveform
regardless of the magnetization direction if the decay angle or the distance
from the center pole is increased. This is because the ratio of harmonic
components indicated in Fig. 9, Fig. 10, and Fig. 11 decreases.
Therefore, the magnetization direction of magnets with a large decay angle
that have a waveform closer to a sinusoidal waveform can be evaluated from
the induced voltage.
If the waveform of the induced voltage is close to a sinusoidal waveform,
the cogging torque gets smaller as indicated by Fig. 12, Fig. 13, and Fig.
14. However, the minimum cogging torque is produced for a parallel anisotropic
pattern that has a 16 degree decay angle and the torque increases again
for a large 18 degree and 20 degree decay angle. This is a result of the
ratio of the 5th order components at 100 Hz increasing.
There is no difference between the waveforms if the cogging torque waveform
for each magnetization pattern is compared. It is difficult to evaluate
the magnetization pattern of the magnets from the cogging torque because
the cogging torque is affected by the geometry of the teeth. |
|
|
|
|
|
|
|
|
  |
