Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Commutation changes when phasing motor
Dear all,

I have experienced the same effect several times and I cannot sort it out. Randomly, when I switch the controller on, and phase the motor, the sense of rotation changes with respect previously. The act of phasing changes the direction of rotation and that produces the position control to be unstable. And what is worst is that I have to retune the motor again until it rotates with the correct sense.
Does anyone knows what am I doing wrong?


Your torque per unit current is proportional to the cosine of the error in determining your phase angle, so is maximum when the error is zero.

Small errors don't reduce torque much. Moderate errors can be insidious because the servo reacts by asking for more current, and you can get overheating much later (when it is difficult to relate the failure to its ultimate cause). Also you have effectively lowered the gain of the loop, which throws your tuning off.

But the real danger is when your error is greater than +/-90 degrees of the commutation cycle. This changes the sign of the torque applied, which creates unstable positive feedback instead of stable negative feedback and can cause a runaway.

So, if I have interpreted you correctly, an improper phasing search move or absolute phasing read is causing your problem. I think that is where you need to look first. I would start by making sure that the "stepper motor" phasing search works reliably and repeatably with an unloaded motor, even if you plan on using a different method in the actual application.
Thanks for your help. I have a brushless AC motor with a resolver and I am using "Four guess method". I always thought that I could use absolute phasing with the resolver but the system does not let me to operate with the same resolver for absolute phasing. Or I do not know how to do it.
Please contact and we can help you troubleshoot your application issues.

Forum Jump:

Users browsing this thread: 1 Guest(s)