A brushless DC motor (also known as a BLDC
motor or BL motor) is an electronically
commuted
DC motor which does not have brushes. The
controller provides pulses of
current to the motor
windings which control the speed and torque of the
synchronous
motor.
These types of motors are highly efficient in
producing a large amount of torque
over a vast
speed range. In brushless motors, permanent
magnets rotate around a fixed
armature and
overcome the problem of connecting current to the
armature.
Commutation with electronics has a
large scope of capabilities and flexibility. They are
known for smooth operation and holding torque
when stationary. Before explaining the working of a brushless DC
motor, it is better to understand the function of a
brushed motor. In brushes motors, there are
permanent magnets on the outside and a spinning
armature which contains electromagnet inside.
These electromagnets create a magnetic field in
the armature when the power is switched on and
help to rotate the armature.
The brushes change the polarity of the pole to
keep the rotation on off the armature. The basic
working principle for the brushed DC motor and for
brushless DC motor are same i.e. internal shaft
position feedback.
Brushless DC motor has only two basic parts: rotor
and the stator. The rotor is the rotating part and
has rotor magnets whereas stator is the stationary
part and contains stator windings. In BLDC
permanent magnets are attached in the rotor and
move the electromagnets to the stator. The high
power transistors are used to activate
electromagnets for the shaft turns. The controller
performs power distribution by using a solid-state
circuit. In an inner rotor design, the rotor is located in the
centre of the motor and the stator winding
surround the rotor. As the rotor is located in the
core, rotor magnets do not insulate heat inside and
heat get dissipated easily. Due to this reason,
inner rotor designed motor produces a large
amount of torque and validly used.
In outer rotor design, the rotor surrounds the
winding which is located in the core of the motor.
The magnets in the rotor trap the heat of the motor inside and do not allow to dissipate from the motor.
Such type of designed motor operates at lower rated current and has low cogging torque.
The advantages of a BLDC motor are:
The disadvantages of a BLDC motor are: