What is the working principle of an AC motor？

The AC motor is mainly composed of an electromagnet winding or distributed stator winding to generate a magnetic field and a rotating armature or rotor. So what is the working principle of an AC motor? Let's take a look next.

Here is the content list:

Three-phase AC motor

Principle of induction AC motor

Principle of Synchronous AC motor

Three-phase AC motor

The stator winding of a three-phase AC motor is basically three coils separated by 120 degrees, which are connected in a delta or star shape. When the AC motor is supplied with a three-phase current, a magnetic field is generated in each coil, and the three magnetic fields are combined to obtain a rotating magnetic field. The current of the AC motor completes a full vibration, and the rotating magnetic field rotates exactly once. Therefore, the number of revolutions per minute of the rotating magnetic field of the AC motor is N=60f. Where f is the power frequency.

Principle of induction AC motor

The induction AC motor is also called "asynchronous motor", that is, the rotor is placed in a rotating magnetic field, and under the action of the rotating magnetic field, rotating torque is obtained, so the rotor rotates.

The appearance and internal structure of induction AC motors. The rotor is a rotatable conductor, usually in the shape of a squirrel cage. The stator is the non-rotating part of the motor, and the main task of the AC motor is to generate a rotating magnetic field. The rotating magnetic field is not realized by mechanical methods. Instead, the AC motor current passes through several pairs of electromagnets, so that the magnetic pole characteristics of the AC motor change periodically, so it is equivalent to a rotating magnetic field. This AC motor does not have brushes or slip rings like a DC motor. According to the type of AC used, there are single-phase AC motors and three-phase AC motors. Single-phase AC motors are used in washing machines, electric fans, etc. Three-phase AC motors are used as power equipment in factories. Through the relative movement of the rotating magnetic field generated by the stator of the AC motor and the rotor winding, the rotor winding cuts off the magnetic induction line to generate an induced electromotive force in the AC motor, thereby generating an induced electromotive force. The current in the rotor winding of an AC motor. The induced current in the rotor winding interacts with the magnetic field to generate electromagnetic torque, which causes the rotor to rotate. As the rotor speed of the AC motor gradually approaches the synchronous speed, the induced current gradually, and the generated electromagnetic torque also decreases accordingly. When the asynchronous AC motor is working in the AC motor state, the rotor speed is less than the synchronous speed.

Principle of Synchronous AC motor

The structure of a synchronous AC motor is roughly the same as that of an AC generator. The basic difference between it and an induction AC motor is that its rotor is a protruding magnetic pole with coils, and another exciter is used to pick up the DC AC excitation current.

Synchronous AC motors are AC motors, and the stator windings are the same as asynchronous motors. The rotation speed of the rotor of an AC motor is the same as the speed of the rotating magnetic field generated by the stator winding, so it is called a synchronous motor. Because of this, the current of the synchronous AC motor is ahead of the voltage in phase, that is, the synchronous AC motor is a capacitive load. For this reason, in many cases, synchronous AC motors are used to improve the power factor of the power supply system.

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