Overview
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SR motors are popular for their robustness and affordability made possible
by the relatively simple structure.
However, their large torque ripple due to the salient stator and rotor
causes noise and vibration, and thus needs to be reduced.
This note presents a case study which shows how the torque ripple varies
with switch timing. |
Torque Ripple
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Fig. 1 shows the torque waveform when voltage is applied to U-phase at
50 degrees (electrical) and turned off at 80 degrees (electrical).
The torque ripple is very large compared to the average torque, and the
torque ripple peaks coincide with the voltage switching timing. |
Comparison of Torque Ripple
Fig. 2 shows the torque ripple obtained from analyses with voltage switch
angles of 55, 56 and 57 degrees applied to U-phase, along with the torque
ripple for 50 degrees. The average torque and the torque ripple are summarized
in Table. 1.
Fig. 2 shows that the switch timing can significantly reduce the torque
ripple. The torque ripple at 56 degrees is 20% of the ripple at 50 degrees.
However, the average torque is also smaller. Further examination is required
to reduce the torque ripple without reducing the average torque, for example,
increasing the number of phases or changing the width of the salient poles. |
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