Brushless DC motor switches the stator and rotor of an ordinary DC motor. Its rotor produces air gap flux for permanent magnet. And the stator is an armature composed of multiphase winding. Brushless DC motor has similar structure with the permanent magnet synchronous motor.
The stator of a brushless DC motor has the same structure with a synchronous motor or induction motor. After multiple phase winding such as three-phase, four-phase, five-phase winding is embedded into the iron core, the winding can be shaped into a star or triangle, and separately connects with each power tube of the inverter so as to make reasonable commutation.
Rotor is mostly made by samarium,cobalt, neodymium, iron, boron or other rare earth materials with high coercivity and high remanence. The magnetic pole be divided into surface magnetic pole, the embedded pole and the annular magnetic poles due to the different placement of the magnetic materials in the magnetic poles. Because the motor body is a permanent magnet motor, brushless DC motor is also called permanent magnet brushless DC motor.
Actually, AC motor is everywhere in our life. For example, it is widely applied in the lampblack machine, washing machine, vacuum cleaner, electric fan, ventilator, hairdryer and etc. How does it work? Take single-phase AC motor, one type of the AC motors, for instance. Single-phase AC motor has two windings, the starting winding and the running winding. The starting winding is connected in series on a large capacitor. When the running winding and the starting winding go through the single-phase alternating current, it reached the maximum value because the capacitor makes the current in the starting winding has an angle of 90 degrees ahead of the running winding in time. Then the same two pulse magnetic fields are formed in the time and space so that a revolving magnetic field is generated in the air gap between the stator and the rotor. In the effect of revolving magnetic field, induction current is produced in a rotor. In the meantime, with the electromagnetic torque produced by the interaction between revolving magnetic field and current, the motor rotates.