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delta wired motor and FOC algorithm using InstaSpin C2000 microcontroller

Alexandre BALDINO
Intellectual 520 points

Hi,

i've evaluated 4 motors, only one of them is a wye connected one.

With this motor, it works perfectly.

With the delta wired motors, the µC gives a speed which is two times higher than the real speed.

I've contacted TI support yet, and transmitted the user.h file.

They said no matter wye or delta connection, it works.

However, even with a correct user.h file, and with an adaptation of resistance values (delta to wye transformation), the microcontroller still gives an incorrect speed.

Has somebody encountered that kind of problem? 

Thank you,

Best regards

Alex

  • 0
    TI__Guru** 118420 points
    FAST does not care if wye or delta. I would suspect that you have an incorrect # of pole pairs listed in your user.h file

    The only reason you would need to know if it is wye or delta is if you are skipping motor ID and just entering the values in user.h. If you do this, you need to convert differently for wye or delta. For the motor ID feature it identifies the correct Rs, Ls, and flux regardless.

    you still need to set the correct # of poles though.

    Is your estimated vs. real speed off by a factor of say 2?
  • 0 in reply to ChrisClearman
    Intellectual 520 points

    I've made a measurement with an oscilloscope, and the speed given by the microcontroller is two times higher than the value of two current period (which corresponds to one turn for a 2-pole pair motor).

    If I change the number of poles (I've put 4 pole-pairs instead of 2), the problem remains. I've checked that the motor had really 4 poles, as announced in its datasheet.

    I don't skip motor ID, so I really don't know where is the problem?

    Best regards

  • 0 in reply to Alexandre BALDINO
    TI__Guru** 118420 points

    FAST estimates the speed in electrical Hz

    gMotorVars.Speed_krpm = electrical Hz * 60 / USER_MOTOR_NUM_POLE_PAIRS

    If you read say 2.4 KRPM with 2 pp, then FAST is estimating 80 Hz
    If you change the poles to 4 pp and command 2.4 KRPM, FAST will be estimating 160 Hz

    The current period should correspond to the electrical frequency from FAST (regardless of how you set your poles)

    Again - FAST does not care how the motor is wound.

  • 0 in reply to ChrisClearman
    Intellectual 520 points

    Hi,

    thank you for your answer.

    When I said switching from 2 pole-pairs to 4pp changes nothing, it's not really true.

    Because switching from 2pp to 4pp gives the right estimated speed if I consider a 2pp motor.

    What I find not coherent is that I have to put 4 pole-pairs in the software to get the right estimated speed for a 2pp motor.

    I mean, on the oscilloscope, although I've put a 4pp software constant, I have to measure the motor current frequency considering a 2pp motor. And in this case it matches. But that sounds not logical.

    Again, I don't have the problem with a star winding motor.

  • 0 in reply to Alexandre BALDINO
    TI__Guru** 118420 points
    if you measure the frequency of one phase current, and you multiply by 120, divide by USER_MOTOR_NUM_POLE_PAIRS and divide by 1000, you will get the value given by gMotorVars.Speed_krpm IQ24 format