The brushless DC motor uses semiconductor switching devices to achieve electronic commutation, that is, electronic switching devices instead of the traditional contact commutator and brush. It has the advantages of high reliability, no commutation spark, low mechanical noise, and is widely used in high-grade recording stand, video recorder, electronic instrument and automatic office equipment.
The brushless DC motor is composed of permanent magnet rotor, multipole winding stator, position sensor and so on. The position sensor converts the current of the stator winding in a certain order according to the change of the rotor position (that is, the position of the rotor magnetic pole relative to the stator winding is detected, and the position sensing signal is generated at the determined position, and the power switching circuit is controlled after the signal conversion circuit is processed, and the winding current is switched according to a certain logical relationship). The operating voltage of the stator winding is provided by the electronic switching circuit controlled by the position sensor output.
There are three types of position sensors: magnetic, photoelectric and electromagnetic.
A brushless DC motor with a magnetically sensitive position sensor has a magnetically sensitive sensor (such as a Hall element, a magnetically sensitive diode, a magnetically sensitive electrode, a magnetically sensitive resistor or an ASIC, etc.) mounted on a stator assembly to detect changes in the magnetic field generated when a permanent magnet or rotor rotates.
A brushless DC motor with photoelectric position sensor is provided with a photoelectric sensor in a certain position on the stator assembly, a light shield is arranged on the rotor, and the light source is a light-emitting diode or a small bulb. When the rotor rotates, due to the action of the light shield, the photosensitive components on the stator will generate pulse signals intermittently according to a certain frequency.
The brushless DC motor with electromagnetic position sensor is equipped with electromagnetic sensor components (such as coupling transformers, proximity switches, LC resonant circuits, etc.) on the stator assembly. When the rotor position of the permanent magnet changes, the electromagnetic effect will cause the electromagnetic sensor to produce a high-frequency modulated signal (its amplitude changes with the rotor position).