Permanent magnet synchronous motor
Compared with the conventional winding synchronous motor, the permanent magnet synchronous motor has no excitation winding and is replaced by a permanent magnet, and the stator structures of the two are basically the same, so that the brush, the field winding and the slip can be omitted at the same time. The ring greatly simplifies the structure of the motor, making it simpler and more reliable.
The working principle begins with the working principle of the traditional electric excitation synchronous motor.
Synchronous motors are available in both rotating pole and rotating armature versions. Since the rotating magnetic pole type has the advantages of small rotor weight, simple manufacturing process, and small current through the brush and the slip ring, the large and medium capacity synchronous motor mostly adopts a rotating magnetic pole type structure.
According to the shape of the rotor, the rotating magnetic pole type can be divided into two types: salient pole type and hidden pole type, as shown in the following figure. Salient poles are often used in applications where low speeds are required.
(a) salient pole type (b) hidden pole type
Schematic diagram of synchronous motor
Synchronous motors, like other rotating machines, consist of two parts, the stator and the rotor. The stator of a synchronous machine is mainly composed of a base, a core and a stator winding.
In order to reduce the hysteresis and eddy current loss, the stator core is stacked with thin silicon steel sheets, and the inner surface of the stator core is embedded with a spatially symmetric three-phase winding.
The rotor is mainly composed of a rotating shaft, a slip ring, a core and a rotor winding. In order to meet the requirements of magnetic permeability and mechanical strength, the rotor core is often forged from high-strength alloy steel.
When the synchronous motor is working, a three-phase symmetrical current is introduced into the three-phase winding of the stator, and a direct current is applied to the exciting winding of the rotor.
When a three-phase alternating current is passed through the stator three-phase symmetrical winding, a rotating magnetic field is generated in the air gap. This rotating magnetic field occurs and is exactly the same as the previous asynchronous motor.
When a direct current is applied to the rotor field winding, a static magnetic field of constant polarity is generated. If the number of magnetic pole pairs of the rotor magnetic field is equal to the number of magnetic pole pairs of the stator magnetic field, the rotor magnetic field is synchronously rotated by the stator rotating magnetic field due to the magnetic field pulling force of the stator magnetic field, that is, the rotor rotates at a speed and direction equivalent to the rotating magnetic field, which is a synchronous motor. The basic working principle.
The rotating magnetic field of the stator or the direction of rotation of the rotor is determined by the phase sequence of the three-phase current flowing into the stator winding. Changing the phase sequence changes the direction of rotation of the synchronous motor.
