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epwm synchronizing

Felix Zhang
Intellectual 645 points


Hi,

I'm using ePWM 1,2,3 with frequency 100kHz, 100kHz, 50Hz.

I synchronized ePWM1(SPWM) and ePWM2 (SPWM) with a phase shift of 180 degree, to drive interleaved flyback.

Now there is a problem when I try to synchronize the ePWM3 (50% duty , 50Hz) to the zero crossing of the output current of flyback, or if I filter (filter function in oscilloscorpe) the SPWM from ePWM1 or 2 to form a sine wave form, there is zero crossing of the sine wave forms, I'd like to output (from ePWM3) 'H' during the sine wave is positive and output 'L' when sine is negative.

the point is how to synchronize this? is it possible to set registers only? or does it need external signal to synchronize?

Regards,

Felix

  • 0
    TI__Mastermind 43730 points

    What are you using the SPWM for? Where is the sine wave coming from?

    Please provide diagram for what exactly you are trying to do.

    Regards

    Manish Bhardwaj

  • 0 in reply to Manish Bhardwaj
    Intellectual 645 points

    ePWM1 is used to drive MOSFET1 while ePWM2 to drive MOSFET2, the two mosfet are interleaved, the current output from MOSFET1 and MOSFET2 is converged and flow through a "H" bridge, which drived by ePWM3.

    ePWM1, ePWM2 => SPWM1, SPWM2, about 100kHz swithcing frequency. => flyback transformer output current to be sine wave form (only positive part, DC), 100Hz.

    ePWM3 => 50Hz PWM => let the half-wave (half sine wave, positive) to be a AC  whole sine wave and feed to grid. 50Hz.

    The sine duty for SPWM1 and SPWM2 are generated from sine table.

    To let the "H" bridge swithing correctly and exactly, I need to synchronize the ePWM3 output 50Hz to either ePWM1 or ePWM2 sine duty crosses zero (flyback transformer output current be zero).

    Regards,

    Felix