HW12 Prob1

I have a somewhat general question about problem 1 of homework 12. There is a statement in the problem description that says, "There is no compensator in the inner wide-bandwidth average current control feedback loop." Does this mean that we are to assume Gc(s)=1 for our bode plots of Ti(s)?

HW 11, Prob 2

I know this is coming in last minute, but I'm stuck on finding the normalized equation describing the DCM input characteristic for the buck-boost. In following the buck example in the book, I looked at the DCM buck-boost averaged large-signal circuit from Fig 11.11. However I'm not sure if I'm supposed to develop equations from this model or simplify it into a DC equivalent model and go from there. Also, am I supposed to try to solve for input current "ig" like in the buck example? Any pointers would be appreciated.

HW#10 prob.1 solution

Hello everyone,
I am aving trouble understanding the solution posted for HW10 prob. 1:

The solution states: Tc(fci) = (Rf*Gio*Ki/VM)*fo^2/(fz*fci) = 1. I do not understand how this expression was arrived at. It appears as though (Rf*Gio*Ki/VM) was assumed to be equal to the flat gain, say, Tco, of the compensator. I don't see how that is true. Even if it were true, I don't see how the rest of the expression makes sense.

I can see that (fci/fi)*(fi/fo)^2 = Tco, the flat gain of the compensated loop gain. However, one cannot know Tco without knowing the fi (the zero of thecompensator)….so there are three unknowns here (fi, fci and Tco).

My thinking would be: Choose fi first (say, for instance, fi = fci/10)….and assume fci = fs/5 = 200/5 = 40kHz. Then fi = 4kHz. Once we know fi, onlythen we can get Tco and then determine fci.

I would really appreciate if someone can shed light on this (or perhaps the grader or the student who did the solution).

Regards,
Nitish

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?

HW10 Problem 1 Spice simulation

Hello, In verifying the solution for the HW10 problem 1 (ACMC), when I simulate the uncompensated loop gain in LTSpice, it matches the hand calculation (here the duty cycle was input using a voltage source). However, as soon as I put the PI compensator in the loop and connect the output to the duty cycle input of the CCM-DCM1 model, all currents and voltages of the converter go out of range (the inductor current becomes in kilo amps and the output of the compensator is in megaVolts)....I am not sure what is going on. I would expect the output voltage of the compensator to be twice the steady state value of the duty cycle (when multiplied by 1/VM would give the duty cycle). Any hints would be greatly appreciated. Regards, nitish

HW10 Prob 1

I'm working on finding the range for Vc in problem one. I found the range of duty cycle using V/Vg=1/D' and used it as a reference for finding Vc. Looking at the mid-band gain I come up with Vm(t)=(R2/R1)Vrf, with Vrf=Rf*I. At turn-off Vm(t) should be at maximum. I used R2=(R1/Vrf)*Vm(t) to find R2. I get R2=350K. This results in a range of .286 to .5 for Vc, using Vc=(10R1/R2)*Vm(t), but it ends up being a lot of mid-band gain for the compensator, ~30dB. I'm not confident in this approach. I'm using Vrf=Rf*I=.05V which is true at steady state but it doesn't account for the inductor current ripple. I haven't had a chance to simulate it yet. Is my lack of confidence in this approach warranted?

New Edtion of text book?

the information presented in this course, that is not in the book is quite valuable. It was mentioned that some of this material would be in the new edition of the book.

Is there any estimate of when the new edition would be made available?

thanks
Mark