Overview
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IPM motors use not only magnetic torque produced by a permanent magnet
and the rotating magnetic field but also reluctance torque produced by
the inductance difference between the d-axis and the q-axis. So, they are
highly efficient motor with high torque. The current phase angle β,
at which torque and efficiency are maximized, varies with rotation speed
and torque. So, the current phase angle β needs to be taken into account
for designing high efficient motor. This note presents the use of magnetic
field analysis to obtain the efficiency of an IPM motor at each current
phase with the rotation speed of 1800 rpm and the current amplitude of
4.0 Ampere when the motor is driven by sinusoidal current. |
Efficiency Characteristics
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Efficiency characteristics are obtained by changing the rotation speed,
amount of current, and current phase, and then obtained characteristics
can be used to create an efficiency map.
As shown in the efficiency graph, the maximum efficiency of 90.5 % is obtained
at β=30 degrees. |
Losses at Each Current Phase/ Magnetic Flux Density Distribution
| By adjusting the current phase, the magnetic flux density of the stator
can be smaller and the iron loss can be reduced. |
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Torque Waveform
| While, the average torque may be reduced, and the torque ripple, the cause
of the noise, may increase. Therefore, the current phase needs to be determined
by taking into account the effect of torque ripple, as well as the importance
of high efficiency |
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