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F28035 HRPWM - Phase shift and channel B

mosin
Expert 1160 points

Hi,

I think I'm facing a resolution problem with my EPwm controlling a phase shift converter. I'm looking at the HRPWm module to see if it could help increase the resolution but I'm not sure it will be fine for controlling the channel B of each of my legs. From what I've read on the forum, HRPWM isn't available on xB other than a complement with no dead-band. I can't add dead band externally so that wouldn't work. I've also read in user guide :

Enables high-resolution period control on the ePWMxA output on devices with a type 1 ePWM module.
See the device-specific data manual to determine if your device has a type 1 ePWM module for
high-resolution period support. The ePWMxB output will have +/- 1-2 cycle jitter in this mode.

Does that mean that the channel A will be HR and B will have dead band but no HR? The duty cycle is fixed at 50% and I only change the phase shift. I need more resolution with it, if I can accept the 1-2 cycle jitter, would that help me? I see the 1-2 cycle jitter ( 16-32ns ), like jitter on my dead band, where my dead band is around 300-400ns. 

Thanks!

  • 0
    TI__Guru 57255 points

    Mosin,

    What you have read is correct.  Channel A will have HR, but channel B will jitter and won't have HR. 

    If possible, the best method is to control all of your FETs with ePWMxA outputs:
    http://e2e.ti.com/support/microcontrollers/c2000/f/171/t/252985.aspx


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Expert 1160 points

    Hi Brett,

    Yes, that would definitly be the best choice but when design is done, it's a bit harder to change the routing! DO you confirm that the jitter, 1-2 cycles, will be lost in the dead band, if my dead band is around 300-400ns?

    Regards,

  • 0 in reply to mosin
    TI__Genius 10820 points

     

    Hi Mosin,

    For a phase shifted full bridge, the power transfer occurs once in each half of the PWM cycle. This means that the jitter on xB output will affect the dead-band (get lost in the dead-band as you say) in one half of the cycle, but in the other half of the switching cycle it may affect the power transfer duty (no matter how big or small a dead-band). This is a serious issue and translates to not applying identical duty cycles to the transformer primary in both halves. This may, over time, cause the transformer to saturate and/or require increased blocking capacitors on the primary.

    I hope this helps.

    Hrishi