Brushless DC motor USES semiconductor switching devices to realize electronic commutator, that is, electronic switching devices instead of traditional contact commutator and brush. It has the advantages of high reliability, no commutating spark, low mechanical noise and so on. It is widely used in high grade recording seat, video recorder, electronic instrument and office automation equipment.
Brushless DC motor is composed of permanent magnet rotor, multi-pole winding stator and position sensor. Position sensing according to the change of rotor position, along a certain sequence of stator winding current converter (i.e. detecting the rotor magnetic pole relative to the position of the stator winding, and in determining the location of position sensor signal, the signal conversion circuit to control the power switch circuit, after processing according to certain logic relation between winding current switch). The working voltage of the stator windings is provided by an electronic switching circuit controlled by the output of the position sensor.
There are three types of position sensor: magnetic-sensitive type, photoelectric type and electromagnetic type.
Brushless DC motor with magnetic-sensitive position sensor, its magnetic-sensitive sensor parts (such as hall element, magnetic-sensitive diode, magnetic-sensitive pole tube, magnetic-sensitive resistor or special integrated circuit, etc.) are installed on the stator assembly to detect the magnetic field changes caused by permanent magnet and rotor rotation.
The brushless DC motor with photoelectric position sensor is equipped with photoelectric sensor at a certain position on the stator assembly, a screen is installed on the rotor, and the light source is a light-emitting diode or small bulb. When the rotor is rotating, due to the role of the shutter, the photosensitive components on the stator will intermittently generate pulse signals at a certain frequency.
Using electromagnetic position sensor brushless dc motor, is in the electromagnetic sensors are installed on the stator component parts (such as the coupling transformer, close to switch, LC resonance circuit, etc.), when the permanent magnet rotor position changes, electromagnetic effect will make the electromagnetic sensor produces high frequency modulation signal (the amplitude changes with the rotor position)