2. • 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.
3. • The brusses in conventional DC motors wear out over
the time and may cause sparking, thus the brushed DC
motors should never be used for operations that
demand long life and reliability.
4. • Let’s see how brushless DC motor works, the rotor of a
BLDC is a permanent magnet, the stator has a coil
arrangement as shown:
5. • By applying DC power to the coil, the coil will energize
and become an electromagnet. The operation of a BLDC
is based on a simple force in reaction between the
permanent magnet and the electromagnet.
6. • In this condition, when the coil A is energized, the
opposite poles of the rotor and the stator are attracted
to each other. As the rotor nears coil A, coil B is
energized.
7. • As the rotor nears coil B, coil C is energized. After that,
coil A in energized with opposite polarity.
8. • This process is repeated and the rotor continues to
rotate.
9. • An ancient humour helping remember it is to think of
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.
10. • Eventhough 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.
11. • Here is the trick to overcome this problem, when the
rotor is in this position along with the 1st coil which
pause the rotor, you can energize the coil behind it in a
such way that, it will push the rotor.
12. • For this instant, a same polarity current is passed
through the 2nd coil.
13. • The combined effect produces more torque and power
output from the motor.
14. • The combined force also make sure that a BLDC has a
beautiful constant torque nature, with this
configuration, two coils need to be energized separatly.
15. • But by making a small modification to stator coil, we
can simplify this process. Just connect one free end of
the coils together. When the power applied between
coils A and B, let’s note the current flow through the
coils. It’s just like the separately energized state.
16. • That’s how a BLDC works, how to know which stator
coils to energize ? How to know when to energize it ?
So we get a continuous rotation from the rotor.
17. • 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.
18. • Most often, a Hall effect sensor is used for this purpose.
19. • The BLDC design being discused for far is known as the
out-runner type. In BLDC runner design, is also available
in market.
20. • We hope you get a nice introduction for the working of
BLDC motors. Thank you.
