There are many kinds of synchronous motor, from the excitation aspect, it can be divided into two kinds, one is electric excitation synchronous motor, the other is permanent magnet synchronous motor. Its structure consists of two parts: rotor and stator. The internal stator structure is basically the same as the general motor, but the difference is that the rotor of the motor is different. The excitation synchronous motor uses the excitation winding, while the permanent magnet synchronous motor uses the permanent magnet rotor. Compared with the permanent magnet synchronous motor, the permanent magnet synchronous motor is simpler in structure, which consists of three parts: rotor core, rotor shaft and permanent magnet. Because a lot of scattered parts are omitted, the motor is more reliable and easier to maintain in the process of operation.