subtractive polarity is shown in Fig. 3, the directions of
two magnetic flux in the saturable yoke are opposite. When
the stator winding current increases, the point that the
magnetic flux in the saturable yoke becomes a zero is
present. Therefore, as the stator winding current increases,
the magnetic flux in the saturable yoke decreases until it
passes through the zero point, then it increases in the
opposite direction against the additive polarity and reaches
magnetic saturation. The magnetic flux of the stator core
main teeth keeps tendency of increase because each other’s
magnetic flux is the same direction.
According to the partial magnetic saturation, the
behavior of the stator self-inductance and the magnetic
flux of the stator core main teeth with instantaneous value
of the stator winding current are shown as Fig. 4. This uses
the electromagnetic field analysis by finite element method
and is computed from the magnetic flux of the stator core
and the stator winding current. When the instantaneous
value of the stator winding current is positive, the rotor is
in position to become the additive polarity. In the case of
the additive polarity as shown in Fig. 2, as the stator winding
current increases at the positive area, the stator selfinductance
decreases rapidly. In case of the subtractive
polarity as shown in Fig. 3, as the stator winding current
decreases at negative area, the stator self-inductance once
increases, decreases rapidly, and the decreases slowly. This
reason is because magnetic offset is present.