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What are the classification methods of AC motors?

AC Motor A motor that can convert AC electrical energy into mechanical energy is called an AC motor. It is widely used in both industrial production and commerce.

A motor that converts AC electrical energy into mechanical energy is called an AC motor. It consists of a rotating rotor and a stationary stator. Usually, the rotor consists of a rotor core and rotor windings, and the stator consists of a stator core and stator windings. The interaction of magnetic fields, consisting mainly of the induction motor and rotating magnetic field principles, is the basis for the operation of AC motors. The current fed into the stator coil by the AC power supply produces a rotating magnetic field, which is similar to magnetic lines of force and forms a toroidal magnetic field in space.

Classification of AC motors

According to the principle of an induction motor, the rotor is subjected to an induced electromotive force from the rotating magnetic field, which causes the rotor to generate a current. Due to the interaction of current and magnetic field, the rotor will rotate and feel the torque. The speed of an AC motor can be varied over a wide range in a number of ways to meet a variety of needs and operating situations. AC motors have the advantages of simple design, reliable performance, wide speed range, low starting current, and a wide range of applications. However, AC motors have some drawbacks, including expensive production costs, difficulty in speed control, poor efficiency, limited starting torque, and harmonic pollution of the grid.

According to the different ways of classification, AC motors can be categorized in the following ways:

Classified according to rotor structure

  • Induction motors: Currently, the most popular and frequently used motors on the market are induction motors. Its rotor generates torque by induction and consists of aluminum or copper guide rings. Induction motors are further classified into two categories: single-phase asynchronous induction motors and three-phase asynchronous induction motors.
  • Permanent Magnet Synchronous Motors: AC motors that use permanent magnets to generate a rotating magnetic field are known as permanent magnet synchronous motors. Its advantages are low vibration, low noise, a high power factor, and high efficiency. However, due to the use of permanent magnet materials in this type of motor, it is more expensive and hence more costly.
  • Switched Reluctance Synchronous Motor: Switched Reluctance A motor is a kind of AC motor that uses a switched magnetic circuit to realize the energy transfer between the stator and rotor. It has the advantages of high efficiency, low noise, low vibration, etc., and has a wide range of applications on some special occasions.

Classification according to the working principle

  • Asynchronous motor: An asynchronous motor is a kind of AC motor that utilizes induction to generate torque, and the rotational speed of an asynchronous motor changes slightly with the change of load. Its rotor moves at a speed slightly lower than the rotation of the magnetic field, so it is called an asynchronous motor. Asynchronous motors are widely used in domestic and industrial applications.
  • Synchronous Motor: A synchronous motor is an AC motor that operates under the synchronization of the stator magnetic field and the rotor magnetic field. The rotational speed of a synchronous motor has a strict correspondence with the frequency of the AC, and the rotational speed is strictly kept constant during operation, and its rotational speed is constant, hence, it is called a synchronous motor. Synchronous motors are widely used in high-precision control and frequency control systems.

Three-phase asynchronous motors can be divided into squirrel-cage and wire-wound according to their rotor structure, of which the squirrel-cage type is the most widely used.


AC motors are widely used in many fields. AC motors are often used in industry to drive a variety of machinery and equipment, including pumps, fans, compressors, rolling mills, cranes, and other heavy equipment. In order to power this equipment, the power supply to the motor must be reliable, efficient, and adjustable. AC motors fulfill these needs. Apart from industrial production, AC motors are also used in a wide range of equipment in the commercial sector, including electric fans, washing machines, air conditioners, elevators, and refrigerators. This is due to the fact that AC motors are able to provide stable speed and efficient energy conversion, and most of these applications require motors that are safe, reliable, energy efficient, and low-noise.

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