Synchronous motors. A synchronous motor is one in which the rotor normally rotates at the same rate as the revolving field in the machine. The stator is similar to that of an induction machine comprising a cylindrical iron framework with windings, generally three-phase, Drive Chain situated in slots around the internal periphery.
usually, synchronous motors are used for applications where precise and continuous speed is necessary. Low power applications of these motors include positioning devices. These are also used in robot actuators. Ball mills, clocks, record gamer turntables also utilize synchronous motors.
The principle of operation of a synchronous electric motor could be understood by taking into consideration the stator windings to be connected to a three-phase alternating-current supply. The effect of the stator current is to establish a magnetic field rotating at 120 f/p revolutions per minute for a frequency of f hertz and for p poles. A direct current in a p-pole field winding on the rotor may also create a magnetic field rotating at rotor rate. If the rotor rate is made add up to that of the stator field and there is absolutely no load torque, these two magnetic fields will have a tendency to align with one another. As mechanical load is applied, the rotor slips back a number of degrees with regards to the rotating field of the stator, developing torque and continuing to be drawn around by this rotating 
field. The angle between the fields raises as load torque is usually increased. The utmost available torque is achieved when the angle where the rotor field lags the stator field is certainly 90°. Software of more load torque will stall the motor.
One benefit of the synchronous engine can be that the magnetic field of the device can be made by the immediate current in the field winding, to ensure that the stator windings need to provide just a power component of current in phase with the applied stator voltage-i.e., the engine can operate at unity power aspect. This problem minimizes the losses and heating system in the stator windings.