Introduction to the Principle of Brushless Motors

A brushless DC motor realizes electronic commutation by means of semiconductor switching devices, replacing the traditional contact commutator and brushes with electronic switching components. It features high reliability, no commutation sparks, and low mechanical noise, and is widely used in high-end tape decks, video recorders, electronic instruments, and automated office equipment.

A brushless DC motor consists of a permanent magnet rotor, a multi-pole winding stator, a position sensor, and other components. The position sensor commutates the current in the stator windings in a fixed sequence according to changes in the rotor position. That is to say, it detects the position of the rotor magnetic poles relative to the stator windings, generates position sensing signals at specified positions, processes these signals through a signal conversion circuit, and then controls the power switching circuit to switch the winding current according to a certain logical relationship. The operating voltage of the stator windings is supplied by an electronic switching circuit controlled by the output of the position sensor. There are three types of position sensors: magnetosensitive, photoelectric, and electromagnetic.

In a brushless DC motor using a photoelectric position sensor, photoelectric sensing components are arranged at specific positions on the stator assembly, a light shield is installed on the rotor, and the light source is a light-emitting diode or a small bulb. As the rotor rotates, the photosensitive components on the stator generate intermittent pulse signals at a certain frequency due to the blocking effect of the light shield.