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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?
The discussion revolves around the relationship between stator current components and torque control in three-phase induction motors (IM). Participants explore the theoretical underpinnings of how the q-axis current influences torque generation, particularly in the context of vector control strategies.
Participants express similar views regarding the decomposition of stator current and its effects on torque, but there is no consensus on the foundational aspects of the relationship or the implications for control strategies.
Some assumptions about the magnetic field interactions and the specific conditions under which the torque control is effective remain unaddressed. The discussion does not resolve the mathematical or theoretical details of the decomposition process.
Thank you. I got it now.Hesch said: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.