Operating Principle Of Brushless DC Motor

Brushless DC motor uses semiconductor switch device to realize electronic commutation, that is, electronic switch device replaces traditional contact commutator and brush. It has the advantages of high reliability, no commutation spark and low mechanical noise, and is widely used in high-end recording stands, video recorders, electronic instruments and automatic office equipment.

Brushless DC motor is composed of permanent magnet rotor, multi-pole winding stator, position sensor, etc. According to the change of the rotor position, the position sensing commutation of the current of the stator winding is carried out in a certain order (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. After the signal conversion circuit is processed, the power switch circuit is controlled, and the winding current is switched according to a certain logic relationship). The working voltage of the stator winding is provided by the electronic switch circuit controlled by the output of the position sensor.

There are three types of position sensors: magnetic sensor, photoelectric sensor and electromagnetic sensor.

For brushless DC motor with magnetic sensitive position sensor, its magnetic sensor components (such as Hall element, magnetic diode, magnetic sensitive transistor, magnetic resistor or special integrated circuit) are installed on the stator assembly to detect the magnetic field changes caused by the rotation of permanent magnet and rotor.

Brushless DC motor with photoelectric position sensor is equipped with photoelectric sensor at a certain position on the stator assembly. The rotor is equipped with a light shield, and the light source is LED or small bulb. When the rotor rotates, the photosensitive components on the stator will generate pulse signals intermittently at a certain frequency due to the effect of the light shield.

Brushless DC motor using electromagnetic position sensor is equipped with electromagnetic sensor components (such as coupling transformer, proximity switch, LC resonant circuit, etc.) on the stator assembly. When the position of the permanent magnet rotor changes, the electromagnetic effect will make the electromagnetic sensor generate high-frequency modulation signal (its amplitude changes with the rotor position).