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F28E120SC: Issue with Open loop control Motor Operation V/F Control

Abhishek Sathyendran
Prodigy 70 points

Part Number: F28E120SC

Dear team,

 

I am currently working on the F28E120SC MCU for the motor control and I am facing a few issues while running the code in the DMC_LEVEL_2 (V/F Control) [tid_mc_labs_f28e12x file ].

I have attached a PDF document below that contains the detailed description of the issues, along with the relevant code and observations.

Kindly review the document and let me know if any additional information is required.

Thank you.

Issues faced in TI Motor Control.pdf 

  • 0
    TI__Expert 6360 points

    Hello,

    DMC_LEVEL_2 is an open loop based method to check the ADC scaling. At the end you have to choose right values for:

    I would bring the angle and phase voltage to scope to see if they are matching. They should look like:

    You can also try starting with DMC_LEVEL_3, where it's a closed current loop.

    Best Regards,

    Masoud

  • 0 in reply to Masoud Farhadi
    Prodigy 70 points

    As the document I have attached above.

    In the document, it can be observed that the phase PWM signals are initially different inphase before they reach the commanded frequency (as shown in Figure 3 and Figure 4).

    I suspect that this behavior may be the reason for the high current flowing at the initial stage.

    Could you please help me understand why this is happening during startup?
    Is this expected behavior before the system reaches the commanded frequency, or could it be related to the PWM configuration or control algorithm?


  • 0 in reply to Abhishek Sathyendran
    TI__Expert 6360 points

    Yes, what you are seeing at startup can be expected. DMC_LEVEL_2 is an open-loop test mode intended mainly to validate the current/voltage sensing path and basic PWM operation. In this build level, the sensed current and voltage are used for observation/verification, not for regulating the motor as in a closed-loop controller. DMC_LEVEL_3 is the step used to validate the hardware with a closed current loop.

    Because this is open loop, during startup the controller applies a generated electrical angle/frequency ramp rather than correcting itself from current feedback. As a result, before the rotor locks into the commanded rotating field, the three phase voltages/currents may not look perfectly balanced or 120° aligned, and a larger startup current can appear if the initial electrical angle, V/f ramp, or voltage magnitude is not well matched to the motor/load. That is why I suggested checking the electrical angle together with the phase voltage on the scope.

    You can verify level 1 items again. Make sure ADC offset calibration, PWM polarity, deadband, phase shift, and current/voltage scaling are all correct, since Level 2 depends on those being clean. And then try DMC_LEVEL_3 since level 3 closes the current loop, it is usually a better step for confirming whether the issue is simply a normal open-loop startup effect or something wrong in sensing/PWM configuration.

    Best Regards,

    Masoud