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motor resistance value detected on higher side

Mika Bay
Intellectual 600 points

I am trying to activate f28054M based low voltage invertor.

The channels A1,B1,A3 are used for current, A6,B6,B4,B7 for voltages. Since all AD channels have PGA's, The voltage and current sense dividers values are adjusetd accordingly.
In lab2b, after I strart detecting motor parameters, the terminal voltage seen is correct(24VDC) indicating that voltage feedback resistances are properly confugered.
However, motor resistnce value detcted is on higher side (0.78ohm phase resistance )instead of (0.4ohm phase resistance) & after the test, motor runs shakey losing control every now and then.
I have rechecked current filter pole value and full scale AdC value and they seem to be fine. In view of this, I have following questions
1. How is motor resistance detected? Is there I can do to check possible problems using CRO?
2. Is there anything I can check to identify issue like monitoring other parameters etc. Especially, how is current per phase mapped from AD value to watch window value?

  • 0
    TI__Guru** 119680 points
    have you ID'd this motor on a TI kit to know expected parameters? is that where you are getting 0.4 ohm as the expected Rs?

    1. this is described in SPRUHJ1

    if you have an LCR you can measure phase-phase and should get pretty close to 2x the Rs returned by motor ID
    2. exactly, while your voltage may be correct the currents may be wrong. you should see if the magnitude of current used in RoverL and Rs testing are as expected based on the RES_EST_CURRENT setting