According to different excitation modes, synchronous motor can be divided into electric excitation synchronous motor, He Yongci synchronous motor.
The rotor is made of a polar type, and the magnetic coils mounted on the pole core are connected in series with each other, and are connected with alternating polarity, and two lead wires are connected to two slip rings mounted on the shaft. The magnetic field coil is excited by a small DC generator or battery. In most synchronous motors, the DC generator is mounted on the motor shaft to supply the exciting current of the rotor pole coil. Because the synchronous motor can not start automatically, the squirrel cage winding is mounted on the rotor as the starting of the motor. The squirrel cage winding is placed around the rotor, and the structure is similar to the asynchronous motor.
When a three-phase AC power source is connected to the stator winding, a rotating magnetic field is generated in the motor, and the squirrel cage winding cuts the magnetic field line to produce an induced current, so that the motor rotates. The rotation of the motor, the speed slowly increased to slightly lower than the speed of the rotating magnetic field, the magnetic field of the rotor coil via the DC power supply excitation, the rotor formed on certain magnetic poles, the magnetic poles will attempt to track the rotating magnetic poles on the stator, so as to increase the rate of the motor rotor and rotating magnetic field rotation until the synchronization so far.
The rotor excitation synchronous motor can be applied to single-phase power supply, and also can be applied to multiphase power supply. In this kind of motor, there is a kind of stator winding which is similar to the stator of a phase splitting motor or multiphase motor, and also has a squirrel cage rotor, and the surface of the rotor is cut into plane. So it is a salient pole rotor. The rotor pole is made of a magnetized steel, and it can always keep magnetism. The squirrel cage winding is used to generate the starting torque, and when the motor rotates to a certain speed, the rotor pole is synchronized with the current frequency of the stator coil. The polarity of the salient pole is induced by the stator, so its number should be equal to the number of poles on the stator. When the motor goes to its proper speed, the squirrel cage winding will lose its function, and the rotation will depend on the rotor and the pole to follow the stator pole so as to synchronize it