Finding duty cycle ratios in full-bridge DC-DC converter

Discussion in 'Homework Help' started by bwc, Feb 19, 2015.

  1. bwc

    Thread Starter New Member

    Feb 19, 2015
    3
    0
    I am asked to find the duty cycle ratios, D1 and D2, and their ripple frequency in the following circuit:

    [​IMG]
    Vo is controlled to provide an average output voltage of 200 V.

    What i've tried doing is setting up this equation:

    V0 = Va - Vb = D1 * Vd - D2 * Vd

    Resulting in:

    200 = D1 * 250 - D2 * 250

    From the looks of it, I need another equation so I can find D1 and D2. Where do I go from here ?

    Thank you.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,965
    743
    Where are D1 and D2, i see Da+/- and Db ??
     
  3. bwc

    Thread Starter New Member

    Feb 19, 2015
    3
    0
    I found these equations (here on slide 28):

    Duty cycle of (TA+,TB-): D1 = ton/Ts =0.5(1+vcontrol/Vtri)
    Duty cycle of (TB+,TA-): D2= (1- D1 )
    Vo = VAN - VBN = D1 Vd – D2Vd
     
  4. bwc

    Thread Starter New Member

    Feb 19, 2015
    3
    0
    Ok, so looking more closely at these equations, assuming Vtri = 250:
    D1 = 0.5 (1+200/250) = 0.9 ; D2 = 0.1

    Is this correct ? how do i find the ripple frequency for this setup ? i'm trying to look for equations, but can't seem to find something for a dc-dc converter.
     
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