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Using TMS320F28035 to generate half bridge switching pattern

Kelvin Leung
Prodigy 20 points
Other Parts Discussed in Thread: TMS320F28035

I am using TMS320F28035 to generate a half bridge switching pattern.  However, the method in epwm document spruge9e seems to have problem.  Can anyone tell me what is the most efficient way to generate this pattern?  Fig. 61 in that document seems not correct.

I mail this question to TI but got no feedback.  Did they make a mistake in this section? 

 

  • 0
    Prodigy 20 points

    I can generate a proper half bridge gate signal with this code.  But not sure if this is the most effective way.  This method need to setup both CMPA and CMPB.  Anyway, don't know why TI make such a mistake in their document.

       EPwm1Regs.AQCTLA.bit.ZRO = AQ_SET; // set actions for EPWM1A
       EPwm1Regs.AQCTLA.bit.CAU = AQ_CLEAR;
       EPwm1Regs.AQCTLB.bit.PRD = AQ_SET; // set actions for EPWM1B
       EPwm1Regs.AQCTLB.bit.CBD = AQ_CLEAR;
       EPwm1Regs.CMPA.half.CMPA = 100; // adjust duty for output EPWM1A & EPWM1B
       EPwm1Regs.CMPB = EPwm1Regs.TBPRD - EPwm1Regs.CMPA.half.CMPA;

  • 0 in reply to Kelvin Leung
    TI__Expert 4120 points

    I will submit a request to have the diagram changed.

    Regarding the waveform generation, you can consider these settings:

    EPwm1Regs.AQCTLA.bit.ZRO = AQ_SET; // set actions for EPWM1A
    EPwm1Regs.AQCTLA.bit.PRD = AQ_CLEAR;
    EPwm1Regs.AQCTLB.bit.PRD = AQ_SET; // set actions for EPWM1B
    EPwm1Regs.AQCTLB.bit.ZRO = AQ_CLEAR;

    This will generate full 50% duty waveforms for HB switching.  You can then use the dead-band module to add dead time between the PWM waveforms.

     

  • 0 in reply to Daniel Chang
    Prodigy 20 points

    Daniel,

    Thanks!  However, 50% duty waveforms is normally used in phase-shift full bridge, the reason is that we can shift the phase to control the power to deliver to the load.  But for half bridge, duty is commonly used to control the power.  If duty is fixed at 50%, the only way to change output power is to change the rail voltage.  To follow textbook, half bridge requires change of duty.  What do you think?

    Kelvin

  • 0 in reply to Kelvin Leung
    TI__Expert 4120 points

    Kelvin,

    Sorry for the late reply.  If you want to generate the waveforms indicated in the (corrected) diagram, you will need to use two Compare registers, one for each PWM channel.

    PWM-A:
        - SET on ZERO event
        - CLEAR on CMP-A UP event

    PWM-B:
        - SET on PERIOD event
        - CLEAR on CMP-B DOWN event

    This will allow you to modify Duty value while maintaing proper phase shift.

  • 0 in reply to Daniel Chang
    Expert 2560 points

    Any idea of how to trigger the ADC in the middle of the pulse?