HW11 P2 resonant intervals

In problem 2 it seems like the resonant intervals should be intervals 3 and 5 only, not intervals 2, 3, 5, and 6 as stated in the problem. Anyone agree or disagree?

HW11, prob1

Hey,

Can anyone give me a hint to solve prob.1 on the homework. I am stuck with the selection of Vg.

HW11, pb 2

Hello All,

In pb 2, how steady-state value of clamped capacitor Vs be estimated ?
In forward converter, we can estimated as if it is operating as PWM.

However, on flyback, if I use the same procedure (PWM), I end up
with Vs equal to V/n, which is going to violate ZVS condition for Q2.

Thanks,
Tanto

Problem 3: Control to Output Transfer Function

I had a conceptual question that someone might be able to answer:

(1) Is the converter control-to-output TF just what is listed on page 300 for the boost converter? I think the parameters for the ZVS-QSW would be the same for the PWM parent converter only because d_hat is the control variable and not fs_hat (like in the one example posted for hw10).

(2) Can anyone explain why the 2 transistor ZVS-QSW is as simple as using the small signal model of the PWM boost converter? (This is on the last slide of the lecture 36).

HW10 P1

From class I got the impression that all converters of the same type follow the same state
plane analysis. I get a little confused when I compare the ZVS-QSW buck converter from class with the ZVS-QSW flyback in this problem. It looks to me like the behavior of the D_2 diode from the class example differs from that of the diode on the secondary of the flyback. In
the buck, when D_2 is conducting, it creates a short across the resonant capacitor so there is no voltage difference across the capacitor. In the flyback when the diode on the secondary is conducting and the transistors on the primary are not, then it seems you would still get a resonant circuit which completely changes the state plane diagram. Am I missing something here?

Hw10, pb2a

Hello,

Did anyone figure out how to solve part a yet ? I am trying to
figure out α - ς. My final equation for JL is:

JL = F/(2*π) * ( (1-μ) * (α - ς) * ( D/F + (1-μ)/μ * D )

where D = (α + ς)/(ωo.Ts)

Thanks

Problem 20.5 Verification

I was wondering if anyone got these numbers:

For 2.38A case: Cr <= 3.8nF and Lr < 6.81e-5 H
For 0.119A case: Cr < = 0.19nF and Lr < 1.37mH

So design: Cr = 0.19nF and Lr < 68.1 microH

n = 0.292

HW8 DCM equations derivation

Has anyone attempted the first question? Any hints on how to start?

F=1, J=2 case

Can someone please describe the state plane in this case. The way I get it does not make complete sense to me becausein this case MA1 = pi, MA2 = pi-2, alpha=beta=pi/2 and two of the centers are at 0,0 one at 2,0 and one at -2,0. So basically the Q2 subinterval does not start where the D1 subinterval ends. This is what I a cannot understand. Any hints?

HW7: Pb1, state plane diagram

In part a of this question where we have to plot the state plane diagram, do we have to give numerical values. Most of the points have numerical values except Jmp, because the problem has no info. about the ripple.

HW7,problem3

Hey ppl,

in prob.3, how is the operation of the src(above resonance) any different from that below resonance, apart from the fact that the direction is now counter-clockwise? I am unable to proceed any further with this problem, so any help is appreciated!

HW7 Q3(b) Above Resonsance State Plane

I found the ellipse equation to be the same as that of 'below resonance' case. Anybody getting a different result?

steady state condition in the half bridge situation

Is the steady state for current that it reaches zero or IL0. If IL0 I just dont see how this state plane can be drawn beacuse of the current changing from -IL0 to +IL0?

Expression for PIV-eliminating IF

Do you guys get the radius as JF? Then PIV=1+JF= 1+IF/(nVg) sqrt(Ll/Cd). I am not having any luck in eliminating L and somehow expr.essing it in terms of Qr

HW 6 ZVS in bridge

In this problem, I think that on the turn off of Q2 the voltage vs goes up from 0 to V_bus and then overshoots and starts ringing. At this point (t_c) we have Q1 and D1 both on. This creates a parallel LC circuit, and when I try to solve Ldi/dt = V_bus = w_0 L dj/dtheta V_bus/R_0 I get that dj/dtheta = 1 which doesn't make sense to me for the circle. Am I misunderstanding the behavior of the circuit at this time?

Also, for the initial condition, can we assume that this is a small enough amount of time that i_L stay steady at -I_L0 for the entire time it is charging the capacitors to get v_s up to V_bus?

State plane plot for forward converter problem

If I understand this correctly, in the case of the forward converter the state plane diagram will look a lot like the very initial problem we did in class (the one with the current src in parallel with the capacitor) except because of -ve sign on nVg which I took as Vbase, it'll be in the second quadrant.

HW6 Reverse Recovery of Freewheeling Diode

I normalized vd and il to put in a state plane diagram. I have an id/Ibase term in my dm/d_theta equation. What do I do with this? I can't make j = (il-id)/Ibase because that would affect my dj/d_theta equation.

On slide 15 of lecture 16, how did Prof. Maksimovic derive m(theta)=1+A*cos(theta + theta_0) and j(theta)=J-A*sin(theta+theta_0)?

Lecture 17: Determining center of circle

I am not able to understand how the professor determined the center of the circle for the buck example by inspection as M. Woudn't we first have to go through the process we went through in the first few slides to first get the equation of the circle?
Thanks

Genv(0)

Has anyone figured out how to determine Genv(0) for the second problem? I was thinking.....

since vs1_hat = 2Vg*cos(pi*D/2)*d_hat..........we can say vs1_hat/d_hat *d_hat/v_hat

= 2*Vg*cos(pi*D/2)*Kpwm = vs1_hat/v_hat

But in the last homework it was more complicated with a partial derivative?

Hi every body

Hi every one

N(s+jws0), N(s-jws0) and Vs1 terms

I need to double check if is correct to choose N(s+jws0)=N(s-jws0)=R and not R(s+jws0)first term and R(s-jws0)second term. If I do it like in first case then I can get rid of 2s term.
Second, how you deal with Vs1. I am thinking Vs1=Is*Z
Z= R/(1+sRC).
Final result sanity check
Genv(s)=-Is*R^2*2*pi*km*1/(s^2+ws0^2)
Please advice.

Problem 2 Hw 4

I just wanted to confirm the transfer function used. Because if this part isn't right, the entire solution is wrong. Like the other problem its just a sanity check.

I get H(s) = R/ (1+sRC) = V/I

Can someone confirm?

Sanity check for values of L and C

Do you get 0.22nF and 11.36mH?

HW3 19.8 c: fm

Can someone please give me a hint about getting an expression for fm?

Prob 19.6 Rcrit

The problem description states that we want Rcrit to be at least 200 Ohms, but while going through steps b & c I never used this value to make any design choices. When I plug my calculations back in I get Rcrit = 175 Ohms for part d, which does not match the design. Should I have used the 200 Ohm value from the problem description in the calculations, or do I probably just have a math error somewhere?

Problem 19.9

Can someone help me compare the Voc value for part A. I used Voc=(4*Vg/pi)*n*||H_inf(s)|| and got Voc=138V. This value seems too big for Vg=12V. Maybe my formula for Voc is wrong! Anybody with the same result?

HW3 pb19.6a R_inf

R_infinity=L/(Cs||Cp) doesnt seem right.

this is second edition book, sixth printing.

I couldn find any errata that talks about this.

Thank you.

In general: tau=RC=L/R, so R=sqrt(L/C)

Conceptual Question Regarding Rcritical

We focused on the LCC resonant tank and found that if R > Rcritical, we are in ZCS mode. If R < Rcritical we are in ZVS mode.

(A) I'm not sure exactly why this is true?
(B) Is this a general statement for any converter....i.e., if R> Rcritical its in ZCS mode?

Voltage and Current Conductions (Problem 19.4)

I'm familiar with the traditional H-bridge in the text with parallel diodes across the transistor. But the homework problem (19.4) I'm having trouble visualizing what is conducting (as far as voltage is concerned) to get the sinusoidal nature.

Let's take below resonance (vc(t) leads Ig(t)] for example. In the first interval, Q1, Q4, D1, D4 must conduct to get positive Ig. This interval can be broken up into 2 subintervals......when Ig is positive and vc(t) is positive......and when Ig is positive but vc(t) is negative. What devices conduct voltage for each of these two subintervals?

Peak transistor current P19.1 e & g

Do we have to give a numerical value for this or its a waveform only?

HW2 P19.1 part d.

I am getting F as a complex number when I try to solve the radical!! What might I be doing wrong here. Anyone else having this problem.

Problem 19.3: Transfer Function

As we have been discussing, we can simply use Figure 19.22 for our analysis. However, the tank network is a parallel L and C. This will lead into a Transfer function problem of H(s) = 1........since all voltages are in parallel........which should not be the case.

Am I misinterpreting something?

19.3: Resonant Tank

Is the resonant tank, all though a dual of the series resonator, acting with the characteristics of a parallel resonant tank? I think this is what dual implies........the dual of series network is a parallel network.....

HW2 Problem 19.1 Part a

I am having trouble visualizing the current ig. I think it would be similar to Figure 19.8, but since it is a half bridge, vs will not go negative, and therefore ig cannot go negative. Also, when vs is zero, ig would also be zero.

Is the current through Cb and L like a sin wave (positive and negative)?

If ig is zero for more than half the period, how does this correlate to the model derived in class? Do I need to determine an equation for the fundamental component, then integrate to get the average ig?

How do you find the value of the phase shift?

Calculating ||H(jw)||

Hey everyone, I need a sanity check. Can someone tell me how to go about calculating the magnitude of a transfer function?

M (conversion ratio) of resonant converters

Can anyone help me with a doubt I have......we've learnt in class that for resonant converters the conversion ratio M evaluates as H(jw_s) and hence we concluded that to change the output voltage we vary the frequency rather than D as in hard-switched or PWM converters. That said, do we then operate these converters always with a duty cycle of D=0.5? Or does it matter if we operate at any other D?

Hw 2 Pb 19.3

Hello All,
I've trouble understanding how the circuit should work in this pb.
Can I have a hint please ?
Thanks,

HW1, Prob 2

Please forgive my lack of recall with respect to DE's. It's been a few years.

For parts b and c I understand that we take the derivative and set it equal to zero to find a max but I'm not sure what we solve for at that point. I assume it's t. I think that would give us the time at which v is at max. Am I correct in this approach?

HW1 Problem 3 Part c

Will the diode current waveform throughout the reverse recovery time look the same as it did in parts a and b? Or do I need to use Qr? How does Qr help me?

I think the intent of the circuit is to turn on Ms to store the energy from the diode D reverse recovery in the inductor Ls. Then at the end of the reverse recovery time, turn on M (zero voltage switching) and shortly after turn off Ms. The energy stored in Ls will then be dumped back to the load via diode Ds. I think we need to equate the energy stored in Ls to the energy that would be lost due to diode reverse recovery. However I don’t know where to start. Any hints?

Switching loss

I am getting this in order of hundreds of Watts. This doesn't sound right.

HW1 Problem 3 Waveform Questions

The diode current waveform shown, along with the description of the voltage waveform in the problem, indicate that the diode current goes negative before the voltage across the diode is affected. How is this possible? Because L and C are large, the fet voltage would start to decrease at the same time the diode voltage starts to increase. Why does the voltage across the fet remain constant until after time interval ta? I would think that the voltage across the fet would start to rise as soon as it starts to conduct current.

If there is a constant 5A through the inductor, it would go directly to the load when the diode is conducting. With a 400V output, 5A * 400V = 2,000 watts. (The problem says 500W.)

Is part b asking what are the switching losses in M, the switching losses in D, and the two added together?

HW1 Prob3 Questions

1) Could someone give me a sanity check on the switching loss of M1 w/o the aux circuit? I'm getting around 30W. Is that in the ballpark?

2) In ECEN 5807 there normally was no switching loss in the diode. The switching loss showed up in the primary switch. In this case, during time tb, there is an increasing voltage across the diode as there is still current decaying to zero. It looks like there must be some power loss in the diode during time tb. Am I correct?

HW1 pb3 D=?

Referred to fig1 (problem3):

Assuming the converter is lossless:

Pin=Pout=500W, Vin=500W/5A=100V

- Volt second balance: D’=Vin/Vout=100V/400V=0.25; D=0.75

- Charge balance: D’*I=Iout=Pout/Vout=500W/400A=1.25A

D’=Iout/I=1.25A/5A=0.25; D=0.75

 

Is D=0.5?

 

Thank you,

Hw1 Pb3

Hello All,

On Pb 3c (the boost conv with aux circuit), can I get a hint
how the aux circuit should work ?

I wonder if the secondary diode will share load current
with first diode when M is off ?

Thanks

Submitting Homework

For off campus students --- Does anyone know who we should submit the homework too? Whose email? Is their a TA for this course? There's one point in Lecture 1 where it could have been mentioned (in introductory comments) where the sound faded out dramatically.

Thanks.

HW1 Problem 2 - Q?

Do we need to consider Q? This would affect the answer for max value of Z.

Hw1, Pb1 Time domain analysis

Hello,

I am not sure if I'm doing it right.
I get the solution for current as:
I(t) = I + (Io-I) * cos(t/sqrt(L*C))

Assuming the result is correct,
peak current for I(t) will depend on value of Io.
If Io > I, then Ipeak = Io, @ cos(t/sqrt(L*C)) = 1
If Io < I, then Ipeak = I, @ cos(t/sqrt(L*C)) = 0

Thanks,
Tanto

Trying to understand the zero loss in M1 during turn-off transition.

From lectures 1 & 2, during the M1 turn-off transition, the energy loss in M1 was said to be zero. However the plot of v_s(t) was shown as a sloping line as it drops from Vdc towards 0. But inductor current must continue flowing with +ve polarity. That means it flows through C1 during the period marked X? I wasnt; sure I understood this very well.

Problem viewing the first lecture.

Is anyone else having problems watching the first class online? For me, it keeps buffering too often and the slides are not following the professor's lectures. Sometimes slide just goes blank.
Thanks

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