In figure 1, the rotor teeth are directly
lined up with
the stator teeth and the flux only has the normal
component so no torque is produced. As the rotor
teeth are displaced from the stator teeth in figures
2, 3 and 4 the motor produces torque. We refer to
this torque as negative because the torque is trying
to pull the teeth back into the stable position. In
figure 5, the flux is split evenly between
the stator
teeth and no torque is produced. By figures
6, 7 and 8 a positive torque is created as the
displaced rotor teeth move to line up with the next
stator teeth. Finally, the rotor teeth line directly up
with the next stator teeth (figure 1).
Each
phase of the motor contributes the sine-
shaped torque displacement curve to the total
output torque of the motor (illustrated below).
The difference between the peak and the valley
is called the torque ripple. The torque ripple
causes vibration so the greater the difference,
the greater the vibration.
With more
phases contributing to the total torque
of the motor, the torque ripple in a 5-phase motor
is greatly reduced over a 2-phase motor. The
difference between the peak and valley in a 2-phase
motor can be as great as 29%, while a 5-phase
is only about 5%. Since torque ripple contributes
directly to vibration the 5-phase motor runs
smoother than the 2-phase.
<
Back - Continue
> |
