Ziya
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I know that decoupling the 3 phase currents we get the id and iq (in rotor frame) currents which control the flux and torque respectively. But where does the relation come from?
Why does q-axis stator current control torque in 3-ph IM?
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Hesch
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I think ( don't know for sure ) that if we have an instant stator current, Istat, that induces a B-field ( Bstat ) which has an angle α to Brotor,
then the Istat is decomposed into Id = Istat * cos α , Iq = Istat * sin α.
In this way Id will not yield any torque, because BId has an angle to Brotor = 0.
BIq has angle to Brotor = 90°, so Iq will yield a torque.
That's why a vector-controlled system tries to control Id to be zero, thus increasing the efficiency of the motor.
Controlling a synchronous motor, you don't need these Id's and Iq's: You just measure the angular position of the rotor by means of an encoder, then induce a current in the stator that will create a Bstat, that is perpendicular to the Brotor.
then the Istat is decomposed into Id = Istat * cos α , Iq = Istat * sin α.
In this way Id will not yield any torque, because BId has an angle to Brotor = 0.
BIq has angle to Brotor = 90°, so Iq will yield a torque.
That's why a vector-controlled system tries to control Id to be zero, thus increasing the efficiency of the motor.
Controlling a synchronous motor, you don't need these Id's and Iq's: You just measure the angular position of the rotor by means of an encoder, then induce a current in the stator that will create a Bstat, that is perpendicular to the Brotor.
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Cdz
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Thank you. I got it now.Hesch said:
I am one year too late
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It may help you to imagine a simplified machine with a one turn armature and permanent magnet field
from a thread last year
that old thread addressed armature reaction
but it's a short hop from there to torque.
https://www.physicsforums.com/threads/armature-reaction-drop.826513/#post-5191404
from a thread last year
that old thread addressed armature reaction
but it's a short hop from there to torque.
https://www.physicsforums.com/threads/armature-reaction-drop.826513/#post-5191404