In order to make the operation more reliable, more efficient
and less noisy, the recent trend has been to use brushless dc motors
They are also lighter compared to brushed motors with the same power output
The brushes in conventional dc motors wear out over time and may cause sparking
Thus the brushed dc motor
should never be used for operations that demand long life and reliability
let's see how a brushless DC motor works
the rotor of a BLDC motor
is a permanent magnet
the stator has a coil arrangement as shown
by applying DC power to
the coil, the coil energize and become an electromagnet
the operation of a BLDC is based on the simple force interaction between the
permanent magnet
and the electromagnet
in this condition when the coil A is energized the opposite poles on the
rotor and stator are attracted to each other
as the rotor nears coil A coil B is energized
as the rotor near coil B coil see is energized
after that coil as energized with the opposite polarity
this process is repeated and the rotor continues to rotate
a humorous analogy to help remember it is
to think about BLDC operation like the story of the donkey and the Carrot
where the donkey tries hard to reach the carrot but the Carrot keeps moving
out of reach
even though this motor works it has one drawback
you can notice that at any instant
only one coil is energized. The two dead coils greatly reduce the power output of
the motor
here is the trick to overcome this problem. When the rotor is in this
position
along with the first coil which pulls the rotor
you can energize the coil behind it in such a way that
it will push the rotor. For this
instant a same polarity current is passed through the second coil
the combined effect produces more torque
and power output from the motor
the combined force also makes sure
that a BLDC has a beautiful constant torque nature
with this configuration two coils need to be energized separately
but by making a small modification to the stator coil
we can simplify this process just connect one free end
of the coils together
when the power is applied between coils A and B
let's note the current flow through the coil
it's just like the separately energized state
that's how a BLDC
works but you might have some intriguing doubts in your mind
how do I know which stator coils to energize
how do I know
when energizer so that I will get a continuous rotation from the rotor
in a BLDC we use an electronic controller
for this purpose. A sensor determines the position of the rotor
and based on this information the controller decides
which coils to energize
most often a Hall effect sensor is used for this purpose.
the BLDC design we have discussed so far
is known as the outrunner type. Inrunner BLDC design
is also available in the market we hope you had a nice introduction on the working
of BLDC motors
thank you