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Original question:

TMS320F280049C: Single Phase Modified Unipolar Inverter PWM Synch

TMS320F280049C: Voltage Source Inverter Reference Design Guide: TIDM-HV-1PH-DCAC.

Aloba Olalekann
Prodigy 100 points
Part Number: TMS320F280049C
Other Parts Discussed in Thread: TIDM-HV-1PH-DCAC, C2000WARE

Hi,

I'm finding the code implementation of TIDM-HV-1PH-DCAC a little different from what was described in the reference design.

In the project code from c2000ware, I find that the two PWM modules are configured for the same frequency as shown below.

Whereas in the reference, it was described that the modulation technique is modified unipolar therefore having both pwm operating at different frequencies as shown below.



Please help clear my confusion. Thanks

  • 0
    TI__Expert 4185 points

    Hello Aloba

    Please see the below line of codes from the project in the file "board.h". When duty is greater than 0, the output of EPWM2 is always 0 and vice-versa. Also, the CMPA value of EPWM2 is always 1 so it just see the polarity of duty and set itself high or low. The polarity of the duty is changed based on the desired frequency of AC output. 

    if(duty>=0)
    {
    // CTR = CMPA@UP , set to 1
    EPWM_setActionQualifierAction(base1, EPWM_AQ_OUTPUT_A ,
    EPWM_AQ_OUTPUT_HIGH, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
    // CTR = CMPA@Down , toggle
    EPWM_setActionQualifierAction(base1, EPWM_AQ_OUTPUT_A ,
    EPWM_AQ_OUTPUT_TOGGLE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    // CTR=0, clear to 0
    EPWM_setActionQualifierAction(base1, EPWM_AQ_OUTPUT_A ,
    EPWM_AQ_OUTPUT_LOW, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
    // CTR = CMPA@Down , clear
    EPWM_setActionQualifierAction(base2, EPWM_AQ_OUTPUT_A ,
    EPWM_AQ_OUTPUT_LOW, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    }
    else
    {
    // CTR = CMPA@UP , clear to 0
    EPWM_setActionQualifierAction(base1, EPWM_AQ_OUTPUT_A ,
    EPWM_AQ_OUTPUT_LOW, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
    // CTR = CMPA@Down , toggle
    EPWM_setActionQualifierAction(base1, EPWM_AQ_OUTPUT_A ,
    EPWM_AQ_OUTPUT_TOGGLE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    // CTR=0, set to 1
    EPWM_setActionQualifierAction(base1, EPWM_AQ_OUTPUT_A ,
    EPWM_AQ_OUTPUT_HIGH, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
    // CTR = CMPA@Down , set
    EPWM_setActionQualifierAction(base2, EPWM_AQ_OUTPUT_A ,
    EPWM_AQ_OUTPUT_HIGH, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    }

    Thanks

    Amir

  • 0 in reply to Amir Hussain
    Prodigy 100 points

    Hi Amir,

    Thanks for your response. But this explanation has not cleared up my confusion.

    The explanation above explains the changing of the duty cycle but not exactly the frequency of operation of the PWM.

    Thanks.

    Aloba.

  • +1 in reply to Aloba Olalekann
    TI__Expert 4185 points

    Hello Aloba

    Please note that the output of a PWM may not necessarily be equal to the frequency for which it is set. The output can be overwritten by the Action Quilifier. With that said, the output of EPWM2 is controlled by the polarity of the duty ratio. So it just depends on the polarity of the duty ratio. I would again suggest to go through the code above I suggested and take reference of the technical reference manual.

    Thanks

    Amir

  • 0 in reply to Amir Hussain
    Prodigy 100 points

    Hi Amir

    Thanks for the explanation. It is now clear to me.

    Warm regards.

    Aloba.

  • 0 in reply to Aloba Olalekann
    TI__Expert 4185 points

    Good to know that.

    Thanks

    Amir