AC motor is a device that converts the electrical energy of alternating current into mechanical energy. An AC motor consists mainly of an electromagnet winding or distributed stator winding used to generate a magnetic field and a rotating armature or rotor. The motor is made by using the phenomenon of rotating an energized coil in a magnetic field by force. There are two types of AC motors: synchronous AC motors and induction motors. The stator winding of a three-phase AC motor is basically three coils separated by 120 degrees from each other, which are connected in a triangle or star shape. When three-phase current is applied, a magnetic field is generated in each coil, and the three magnetic fields are combined to obtain a rotating magnetic field. AC motor consists of stator and rotor, and there are two kinds of AC motors: synchronous AC motor and induction motor. Both types of motors generate rotating magnetic field by passing AC current into the stator winding, but the rotor winding of synchronous AC motor usually needs to be supplied with DC current (excitation current) by the exciter, while the rotor winding of induction motor does not need to be fed with current. The stator winding of a three-phase AC motor is basically three coils separated by 120 degrees from each other and connected in a triangle or star shape. When the three-phase current is applied, a magnetic field is generated in each coil, and the three fields are combined to obtain a rotating field. When the current completes one full vibration, the rotating magnetic field rotates exactly one week, therefore, the revolutions per minute of the rotating magnetic field N=60f. The equation f is the frequency of power supply. AC motors can be classified into synchronous motors and asynchronous motors (or non-synchronous motors) according to the rate of rotor rotation. The rotor speed of a synchronous motor is constantly the same as the speed of the rotating magnetic field regardless of the load, so this speed is called synchronous speed, and as mentioned above, it is determined only by the frequency of the power supply. The speed of asynchronous motor is not constant, but depends on the size of the load and the voltage of the power supply. Among three-phase asynchronous motors, there are non-rectifier motors and rectifier motors. Most of the asynchronous motors in practice are induction motors without rectifier (but the parallel and series three-phase asynchronous rectifier motors have the advantages of adjustable speed in a wide range and high power factor), and its speed is constantly less than the synchronous speed. Main applications AC motor has higher working efficiency, and no smoke, dust and smell, no pollution to the environment, and less noise. Because of its series of advantages, it is widely used in various aspects such as industrial and agricultural production, transportation, national defense, commercial and household appliances, medical electrical equipment, etc.