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IFOC driving an asynchronous motor at 400Hz

Leong
Expert 1070 points

Hi, I wonder if any one has done vector control of a 400Hz 4 pole induction motor with C2000? The vector control has to be current driven (current inner loop). I wonder if the microprocessor is fast enough to close this current loop? any reference is appreciated. What may be the typical "red flags" in such control schemes?

  • TI__Guru** 119680 points

    We haven't personally done it that I know of, but there is no reason the 28x couldn't do this.  From a "fast enough" stand point it is tied more to

    Loop or PWM Frequency    /    Processor Cycle time  = # of cycles available 

    # of cycles needed   /    # of cycles available = Processor Usage

     

    Inner current / Outer speed Sensorless FOC for ACI is typically in the low 1000's of cycles for a 28x device (most dependent on the type of observer used, this could double the cycles).

     

    I believe with a 400Hz drive you have to substantially raise the bus voltage to get needed torque don't you?  What application are you looking at this technique for?

  • Genius 5170 points

    Well, roughly your PWM switching frequency should be atleast 25 times your maximum fundamental frequency ( this is just a "rule" many follow) ... your maximum fundamental frequency is 400Hz and 25 times of that is 10kHz .. therefore you should be able to close current loops without much issue. However, you will need to watch out for other system related issues like over heating of your IGBTs (higher switching frequency) , mechanical structure ... a 4 pole machine at 400Hz will rotate at 12000 RPM , and of course your basic inverter design which will need to provide enough currrent to overcome huge back EMF at 12K speed. Are you planning to manage current cycle by cycle even at that speed? Or will you implement some sort of peak current control ? Bottom line , your challenge will come more from power electronics design than from controller capability. Good luck.

  • in reply to Arefeen
    Expert 1070 points

    Thank you both for the insight. back emf is indeed a problem at high rpm thus the regulation of the current at that speed. Arefeen, can you elaborate the peak current control a bit? Do I need to implement 2 controllers one (peak current )for high speed one (foc) for low speed? What are the common practices to digitally control induction machines at that high rpm? Thanks