Overview
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In a permanent magnet motor, the magnets are exposed to the demagnetization
field of the coils. The demagnetization generally worsens the motor performance,
and it is important that the demagnetization effect is carefully evaluated
with magnetic field analysis.
This example presents the use of a magnetic field analysis to evaluate
the demagnetizing ratio distribution of an of an SPM motor by changing
the current flow. |
Flux Density Distribution
| Fig. 1 shows the flux density distribution at an angle of 20 degrees with
current of a 15 A. Demagnetization occurs at the end of the magnet because
the orientation of the magnet and the direction of the flux generated by
the rotating magnetic field are opposed. |
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Operating Point
| Fig. 2 shows the points where the operating points are evaluated, and Fig.
3 shows the operating points at the selected points when the current flow
is 15 A. The graph shows the irreversible demagnetization in Point 1Position
A, because the operating point cannot track back to the original BH curve.
The size of the reverse magnetic field imposed upon the points is also
illustrated on the graph. |
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Permeance Coefficient Distribution
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Fig. 4 shows the permeance coefficient distribution of the magnet when
the motor is stationary with no load. The contour plot is shown in two
colors, that are red and purple. The knee point of the magnet used for
the analysis is 0.699. The figure shows that the demagnetization hardly
occurs when the motor is stationary with no load. |
Demagnetizing Ratio Distribution
The demagnetizing ratio* is evaluated by the setting the criterion as the
demagnetizing state when the motor is stationary with no load. Fig. 5 shows
the demagnetizing ratio for a motor that is driven for one period of the
electric angle. As the current flow increases, both the demagnetizing area
also increases, and the value of the demagnetization increases as well.
*The demagnetizing ratio shows if the magnet has been demagnetized from
a certain state which is used as the criterion. |
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