AC motors are generally divided into synchronous and asynchronous motors

1,AC synchronous motors:The rotor is constituted by a permanent magnet material, so that the rotation of the motor with a stator of the rotating magnetic field changes, the frequency response of the rotor speed can be changed, and the rotor speed = speed of the stator, so called "sync"

2,AC asynchronous motors:The rotor is constituted by the induction coil and the material. After rotation, the stator generates a rotating magnetic field, the magnetic field cutting rotor induction coil , the rotor coil induced current,then the rotor induced magnetic field , induced magnetic field follow the change of rotating magnetic field of the stator, the rotor is always less than the change in the magnetic field of the stator, once it is equal to no change induction coil cutting rotor in the magnetic field, rotor coil will be no induced current, the rotor magnetic field disappears, and the rotor and the stator produce stall speed difference regained induced current. So there is a critical parameter for AC induction motor is the speed difference ratio of slip speed of the rotor and the stator.

3,Corresponding AC synchronous and asynchronous motors have matched synchronous and asynchronous inverter drives, servo motors have AC synchronous servo and AC induction servo, of course, common frequency inverter where AC induction, AC synchronous servo is common