Electronically commutated motor

Brushless DC electric motor (BLDC motors, BL motors) also known as electronically commutated motors (ECMs, EC motors), or synchronous DC motors, are synchronous motors powered by DC electricity via an inverter or switching power supply which produces an AC electric current to drive each phase of the motor via a closed loop controller. The controller provides pulses of current to the motor windings that control the speed and torque of the motor.

The construction of a brushless motor system is typically similar to a permanent magnet synchronous motor (PMSM), but can also be a switched reluctance motor, or an induction (asynchronous) motor.

The advantages of a brushless motor over brushed motors are high power to weight ratio, high speed, and electronic control. Brushless motors find applications in such places as computer peripherals (disk drives, printers), hand-held power tools, and vehicles ranging from model aircraft to automobiles.

Brushed DC motors are a mature technology, invented in the 19th century, but brushless DC motors are a relatively recent advance, made possible by the development of solid state electronics in the 1960s with further improvements in the 1980s thanks to better permanent magnet materials.

An electric motor develops torque by magnetic force between rotating magnets on the rotor, the turning part of the machine, and stationary magnets on the stator which surrounds the rotor. One or both sets of magnets are electromagnets, made of a coil of wire wound around an iron core. Electric current through the wire winding creates the magnetic field, providing the power which runs the motor. However, each time the rotor rotates by 180° (a half-turn), the position of the north and south poles on the rotor are reversed. If the magnetic field of the poles remained the same, this would cause a reversal of the torque on the rotor each half-turn, and so the average torque would be zero and the rotor wouldn't turn. Therefore, in a DC motor, in order to create a torque in one direction, the direction of electric current through the windings must be reversed with every 180° turn of the rotor (or turned off during the time that it is in the wrong direction). This reverses the direction of the magnetic field as the rotor turns, so the torque on the rotor is always in the same direction.

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