A
synchronous electric motor is an
AC motor in which, at
steady state, the rotation of the shaft is synchronized with the
frequency of the supply current; the rotation period is exactly equal to an integral number of
AC cycles. Synchronous motors contain multiphase AC
electromagnets on the
stator of the motor that create a
magnetic field which rotates in time with the oscillations of the line current. The
rotor with permanent magnets or
electromagnets turns in step with the stator field at the same rate and as a result, provides the second synchronized rotating magnet field of any
AC motor. A synchronous motor is only considered
doubly fed if is supplied with independently excited multiphase AC
electromagnets on both the rotor and stator.