What is a brushless motor?
A Brushless DC (BLDC) motor is a rotating electric machine where the stator is a classic
three-phase stator like that of an induction motor and the rotor has surface-mounted permanent
magnets. In this respect, the BLDC motor is equivalent to a reversed DC commutator motor
(or brush motor), in which the magnet rotates while the conductors remain stationary. In the DC
commutator motor, the current polarity is altered by the commutator and brushes. On the contrary,
in the Brushless DC motor, the polarity reversal is performed by power transistors switching in
synchronization with the rotor position. Therefore, BLDC motors often incorporate either internal
or external position sensors to sense the actual rotor position or the position can be detected
without sensors. The BLDC motor is driven by rectangular voltage strokes coupled with the given
rotor position. The generated stator flux interacts with the rotor flux, which is generated by a
rotor magnet, defines the torque and thus speeds of the motor. The voltage strokes must be properly
applied to the two phases of the three-phase winding system so that the angle between the stator
flux and the rotor flux is kept close to 90° to get the maximum generated torque. Due to this
fact, the motor requires electronic control for proper operation.
