An electric machine selectively operates as a generator mode or a motor mode.
The electric machine includes a stator core, a multi-phase armature winding, a
field coil, a moving core having a plurality of salient poles so as to move relative
to the stator core to cross the magnetic field. Field current is supplied to the
field coil differently according to operation mode. A portion of the armature winding
is short-circuited to form an additional magnetic field that has a phase different
from the magnetic field of the field coil. Therefore, the rotary core moves relative
to the stator core when the operation mode is in the motor mode.
