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C2000WARE-MOTORCONTROL-SDK: Motor Control Problems

Javier Vara
Expert 1585 points
Part Number: C2000WARE-MOTORCONTROL-SDK
Other Parts Discussed in Thread: MOTORWARE

Hi,

we have developed a custom inverter based on the F280049 processor and the c2000 motor control sdk libraries for a high power inverter (200kW peak) driving a high power motor (200kW). Nominal DC voltage is 700V and maximum phase current is 450Arms (we use hall effect sensors). I have two separate, possibly unrelated, questions:

  • The inverter works reasonably well at medium to low current levels but when getting close to full current (450Arms), the system controller gets very oscillatory or unstable until the point the current exceeds the trip level (800Amps peak) and the inverter goes into fault. I believe this is due to the motor iron reaching saturation which changes the characteristics of the system thus affecting the controller and instabilities. Is there any way to improve the controller to deal with this situations?
  • Our application requires the inverter to be stable even with variations of the input DC voltage (which can range from 700V down to 500V). We have noticed that the stability and controllability of the system is affected by variations on the DC voltage. Is there a way to compensate for this? I remember, before C2000 motor control sdk, when motorware existed there was an option named "DC voltage compensation". If I remember correctly, such option would modify the Kp gains to the current controller depending on the DC voltage, I don't know if this is the kind of thing I am looking for? or is this something else? I haven't seen such thing on the C2000 motor control labs. Would this help?

Some help would be very much appreciated. Thanks.

  • 0
    TI__Guru** 110290 points

    Q1: Please check if the peak/maximum current is over the ADC input range. And you might check with the motor manufacturer if the inductance will change significantly when the phase current of the motor increases. If yes, you might add a function to online change the motor parameter based on the inductance vs. current curve provided by the motor manufacturer.

    Q2: It's not necessary for motor control SDK since the output of the current PI regulator is an absolute voltage that is not impacted by the dc-link voltage changes.

  • 0 in reply to Yanming Luo
    Expert 1585 points

    Q1: I guess this would improve the angle estimation? We also have the possibility to run using an encoder (which we have) and got similar results. We have run in the past, same amount of current on a higher current motor (much below saturation) with much better results, which is why we believe this is related to the saturation. Is there any way to improve the control when running a little bit into saturation? I have noticed as well that the current waveform gets slightly distorted which again, I believe has to do with the saturation.

    Q2: thanks

    Q3: Is there in c2000 something like 5th / 7th harmonic suppression? I believe this could also help with the control problem.

  • 0 in reply to Javier Vara
    TI__Guru** 110290 points

    Q1: Yes. Both the FOC and estimator need correct current&voltage feedback signals for current closed-loop and angle estimation. You might increase the dc-link voltage or run the motor with a slight load to see if the issue still appears. As you mentioned above, do you meet the same problem when you run the motor using the sensored-FOC with encoder? If yes, you have to check if the current/voltage sensing circuit is good for motor control on your board.

    Q3: No such example. You might try it by yourself.