Tuesday, April 19, 2011

HW11 Problem 1

This seems like a straightforward problem to me, but I am having trouble getting results for the CCM/DCM boundaries that make sense.

The fundamental difference for the buck-boost compared to the boost is that the inductor current is not equal to i_g, but rather only equal to i_g when the MOSFET is on and equal to the output current otherwise.

I used the normal buck-boost conversion ration to determine my d(t) equation, and I replaced d(t) in the inductor current equation with this. Then I calculated the CCM boundary by < delta i_L(t). This is a little more complicated then the boost since in the boost = .

Basically, I am getting a value for R_e,crit that is a function of Ts, L, and R. It is not dependent on V or v_g so it creates a hard boundary for CCM/DCM. This doesn't seem right. Does anyone see where my approach might be wrong?
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3 comments:

  1. VojkanApril 20, 2011 at 7:55 AM

    Re depends on V and vg, since duty cycle depends on V and vg.

    CCM boundary: iL>delta_iL; where
    iL=ig/d=vg/(Re*d)

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  2. AudreyApril 20, 2011 at 4:15 PM

    Thanks for the tip. I was trying to make the equation for iL way too complicated. Sometimes its hard to see the obvious answers.

    ReplyDelete
  3. KAMIApril 20, 2011 at 4:42 PM

    Guys, thank you for your help.
    after finding Re in function of L Ts V and Vg, i replace Re by Vg^2/Pin and start numerical values to find L but i found L around 1H which is wrong. Did i miss something?

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