What is the principle of AC servo controller

The rotor of AC servo controller is usually made into squirrel cage type, but in order to make AC servo controller have wide speed regulation range, linear mechanical characteristics, no "rotation" phenomenon and fast response performance, it should have two characteristics: large rotor resistance and small rotation inertia compared with ordinary motor. At present, there are two types of rotor structures widely used: one is the squirrel cage rotor made of high resistivity conductive materials. In order to reduce the moment of inertia of the rotor, the rotor is made slender; The other is the hollow cup-shaped rotor made of aluminum alloy. The cup wall is very thin, only 0.2-0.3mm. In order to reduce the magnetic resistance of the magnetic circuit, a fixed inner stator should be placed in the hollow cup-shaped rotor Hollow cup rotor has small moment of inertia, rapid response and stable operation, so it is widely used. When the AC servo motor has no control voltage, there is only the pulsating magnetic field generated by the excitation winding in the stator, and the rotor is stationary. When there is a control voltage, a rotating magnetic field is generated in the stator, and the rotor rotates in the direction of the rotating magnetic field. When the load is constant, the speed of the motor changes with the size of the control voltage. When the phase of the control voltage is opposite, the AC servo controller will reverse.