1. Basic structure of synchronous motor
The stator of a synchronous motor is called an armature, and its structure is the same as that of a three-phase asynchronous motor, consisting of a stator core, a stator winding, a machine base, and an end cover. The stator core is composed of silicon steel sheets, and three-phase symmetrical windings are embedded in the core slots.
The rotor consists of a rotor core, field winding, starting winding, and shaft. The rotor core is made of cast or forged steel on which the field winding is wound. The excitation winding is connected with the excitation power supply and connected with the excitation current. The starting winding is composed of copper strips embedded on the surface of the magnetic poles. The two ends of the copper strips are connected with copper rings, which is the same as the squirrel-cage rotor of the asynchronous motor. The rotor of the three-phase synchronous motor has a hidden pole type and convex two types.
(1) hidden pole type
The invisible pole rotor core is cylindrical, with slots on the surface, and the field winding is embedded in the slots, and the air gap between it and the stator core is relatively uniform.
(2) salient pole type
The excitation winding of the salient pole rotor is concentrated on the iron core column between the two magnetic poles, and the breath between the stator core and the stator core is uneven.
2. The basic principle of synchronous motor
1) Three-phase AC power is added to the stator winding, and a rotating magnetic field with a rotation speed of n0 is generated through three-phase symmetrical alternating current; the rotor excitation winding is fed with DC current to generate a static magnetic field with constant polarity.
2) After the rotor is started in a certain way, when the speed n is close to n0, if the number of magnetic pole pairs of the rotor magnetic field is equal to that of the stator magnetic field, according to the principle of magnetic poles attracting each other, the magnetic poles of the stator and rotor magnetic fields will tend to Alignment, when the synchronous motor is actually running, due to the existence of resistance, the magnetic pole axis of the rotor always lags behind the axis of the rotating magnetic field by an angle θ, thus generating an anisotropic magnetic field pulling force, that is, electromagnetic torque, which prompts the rotor to move synchronously with the rotating magnetic field, that is n=n0. This is the basic principle of synchronous motor.