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Permanent magnet synchronous motor using field orient control

aadhu ais
Prodigy 20 points

In PMSM motor control we are considering that the flux component id=0 what if id is not equal to zero? ie, in practical application a small value appears for id. when there is a value for id how will the whole equation change? how will the shift occur? How can we COMPENSATE this?  Is there any available compensation terms for that?And also we are considering that the angle between  the rotor is 120 degrees. but in practical situation the angle varies due to fabrication error from 120 to some other degrees . how will that effects the  id, iq ?

Thanks,

  • 0
    TI__Guru 58810 points
    Hi Aadhu ,

    Have moved this into Motor driver forum .
  • 0
    TI__Guru** 118350 points
    you don't have to control to Id = 0
    it is the most common, but there are cases where you change the Id component to control to a negative (field weakening - advancing the stator flux) or positive (field boosting - reducing the stator flux angle). You may also do this for synchronous motors with very high saliency (interior PM motors) to maximize the torque interaction. Further, there are many different types of current control that can be done. A popular method for these types of motors is called cross coupled current control.

    considering you are a student I suggest you find some good text books on the topic at your university or on-line.
  • 0
    Prodigy 20 points

    thanks,

    when controlling the actual motor a small value appears in vd that doesn't shift correctly to compensate and obtain the correct waveform for valpha and vbeta. and the amplitude also should vary. is there any compensatory terms available for this shift to occur.

    i checked the maximum of books available, and went through almost every papers related. kindly suggest the book or any paper that will do some help

  • 0 in reply to aadhu ais
    TI__Expert 4760 points

    Hello aadhu,

    What you are seeing is very common.  Even though you are trying to regulate your id current to zero, it may not actually achieve this value for 2 reasons:

    1.  Depending on your PI gains, you may not be able to completely compensate for the natural cross-coupling effect inside of a PMSM motor between the d and q axes.  This is especially evident during transients in iq at high speeds.  A feedforward cross coupling network beteween the two PI current regulators can help with this effect.

    2.  Depending on your sampling frequency in relation to the speed of the motor, there is a delay from when you sample the rotor flux angle and when the voltage calculated from that angle actually is applied to the motor windings.  This will cause a slight misalignment where part of your iq current actually bleeds over onto the d axis.  You can correct this by using phase compensation for the angle used by the reverse park transform which is dependent on sampling frequency and motor speed.

    As long as your Id current is relatively small, it is no big deal, as it simply implies that the angle alignment of your stator current vector is off by a few degrees.  If you look at the motor's torque vs. angle curve, this is at the peak of the sinusoidal curve which is very flat, so the effect on MTPA is minimal.

    Regards,

    Dave