We have a small BLDC motor(160W) and the load of the motor is constant. I want to control the speed of the rotor.
We don't have access to the rotor, so we should use sensorless method, but we have problem in detecting the rotor position.
The motor is 4 poles and 3 phase BLDC.
Can anybody help us?
Additional to the first answer this link might help a little bit to distinguish the different states of commutation and so on:
http://preview.tinyurl.com/kssnfua
Page 15ff
Regards
you can make it by using an encoder or look at this;
[1] ESTIMATION OF SPEED AND ROTOR POSITION OF BLDC
MOTOR USING EXTENDED KALMAN FILTER Lenine, D. ; Reddy, B.R. ; Kumar, S.V. Information and Communication Technology in Electrical Sciences (ICTES 2007), 2007. ICTES. IET-UK International Conference on Publication Year: 2007 , Page(s): 433 - 440
Dear Majidreza,
Yes, you have many options. Mr. Alireza explained the theory very well. You can measure the induced EMF from the stator (it is always star connected) for the back emf zero crossing method which is very suitable in your case. If you know when and where the zero crossing of the trapezoid shape emf occure, you know exactly the position of the PM for each electromagnetic commutation. In your case, since your BLDC is 4 pole, commutation happen every 90 electrical degree per phase and consequently you will have commutation every 30 electrical degree in the motor. This requires you to use H bridge inverter for the DC out put to effectively control the speed.
Can you give additional name plate data like rated values of input voltage, current, torque, power, speed etc and the range of speed variation you desire to acquire.
Best regards
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