An electric motor is an electromagnetic mechanical device that converts electrical energy and mechanical energy into each other. There are generally two application forms of electric motors. First, converting mechanical energy into electrical energy,

which is called a generator. Second, converting electrical energy into mechanical energy, which is called a motor. This article mainly introduces the classification and working principle of electric motors.

IClassification of Electric Motors

1. Classification by Working Power Supply

It can be divided into DC motors and AC motors, among which AC motors are classified into single-phase and three-phase types.

2. Classification by Structure and Working Principle

It can be divided into DC motors, asynchronous motors and synchronous motors.

The rotor speed of an asynchronous motor is always slightly lower than the synchronous speed of the rotating magnetic field.

The rotor speed of a synchronous motor is independent of the load and remains at the synchronous speed at all times.

3. Classification by Starting and Operation Mode

It can be divided into capacitor-start single-phase asynchronous motors, capacitor-run single-phase asynchronous motors, capacitor-start and run single-phase asynchronous motors and split-phase single-phase asynchronous motors.

4. Classification by Application

It can be divided into drive motors and control motors. Drive motors can be further divided into electric tool motors, household appliance motors and motors for other general small mechanical equipment. Control motors include stepper motors, servo motors, tachogenerators and so on.

5. Classification by Rotor Structure

It can be divided into squirrel-cage asynchronous motors and wound rotor induction motors.

6. Classification by Working Speed

It can be divided into high-speed, low-speed, constant-speed and variable-speed motors.

IIWorking Principle of Electric Motors

The working principle of an electric motor is based on the laws of electromagnetic induction and electromagnetic force. When an electric motor performs energy conversion, there must be two main components that can move relatively:

a component that generates a magnetic field, and a component that induces electromotive force and carries the working current. Of these two components, the stationary one is called the stator, and the rotating one is called the rotor. There is an air gap between the stator and the rotor, and the rotor rotates around it.

Electromagnetic torque is caused by the interaction between the magnetic field in the air gap and the magnetic field generated by the current in the induction component. By the action of electromagnetic torque, a generator absorbs mechanical power from the mechanical system, and a motor deliv-

ers mechanical power to the mechanical system. Different types of motors are formed due to the different ways of generating the above two magnetic fields.