"Vaithy" wrote in message
ups.com...
I am currently working with torque control of a BLDC motor. Hall effect
sensors are used to determine the position of rotor(permanent magnet).
The stator is energized by 3-phase current.
Depending upon the signals recieved from the hall effeect
sensors,particular stator coils are energized (commutation ). I am not
clear why the position of rotor needs to be determined to keep the
motor running.
Need some help.

I'm no expert on brushless motors, but the general idea is to energise
each of the three coils in the correct timing and sequence to push/pull the
rotor in the required direction. If your timing is out, the motor will not
run reliably at the required speed and in fact may even be pulled backwards.
The hall sensors allow your controlling software to know the exact
position of the rotor so that you know when to energise the next coil in the
sequence.
In other words, the rate at which you energise the coils determines the
speed of the rotor, but without the hall effect sensor's position feedback
there'd be no way of knowing where the rotor is and which coil to energise
next.
Hope this helps a little.

.... TDF