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Working Principle of Brushless Motor

Brushless DC motor uses semiconductor switching devices to realize electronic commutation, that is, electronic switching devices instead of traditional contact commutators and brushes. It has many advantages, such as high reliability, no commutation spark, low mechanical noise, etc. It is widely used in high-end tape recorders, video recorders, electronic instruments and automated office equipment.

Brushless DC motor is composed of permanent magnet rotor, multi-pole winding stator, position sensor and so on. The position sensor converts the stator winding current according to the change of rotor position in a certain order (i.e. detecting the position of the rotor pole relative to the stator winding, and generating position sensing signal at the determined position, then controlling the power switch circuit after signal conversion circuit processing, and switching the winding current according to a certain logical relationship). The operating 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.

A brushless DC motor with magnetic position sensor is used. Its magnetic sensor components (such as Hall element, magnetoresistive diode, magnetoresistor, special integrated circuit, etc.) are mounted on the stator module to detect the magnetic field changes caused by the rotation of the permanent magnet and the rotor.

The brushless DC motor with photoelectric position sensor is equipped with photoelectric sensor in a certain position on the stator assembly, and the rotor is equipped with a light shield. The light source is light emitting diode or small light bulb. When the rotor rotates, the photosensitive components on the stator will generate intermittent pulses at a certain frequency due to the role of the shading plate.

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