Variable-reluctance Stepper Motors

Variable-reluctance (VR) Stepper Motors

The variable-reluctance (VR) stepper motor differs from the PM
stepper in that it has no permanent-magnet rotor and no residual
torque to hold the rotor at one position when turned off. When the
stator coils are energized, the rotor teeth will align with the energized
stator poles. This type of motor operates on the principle of minimizing
the reluctance along the path of the applied magnetic field. By
alternating the windings that are energized in the stator, the stator field
changes, and the rotor is moved to a new position.
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Variable reluctance stepper

The drive waveforms for the 3-φ stepper can be seen in the
“Reluctance motor” section. The drive for a 4-φ stepper is shown in
Figure . Sequentially switching the stator phases produces a rotating
magnetic field which the rotor follows. However, due to the lesser
number of rotor poles, the rotor moves less than the stator angle for
each step.
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Switched Reluctance Motor

switched reluctance (also known as variable reluctance) motor has
no permanent magnets or brushes. Coils connected in series around
a pair of opposite stator poles are energised by a DC current to create
lines of magnetic flux. This causes a pair of teeth on the iron rotor to
align themselves with the stator poles. This sequence is continued around
the stator poles causing the rotor to rotate. Suitable for high torque and
high speed applications
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