Problem with QSWsynch1pt Excel sheet crashing?

Hey everyone.  Is anyone else having a problem with the 'QSWsynch1pt.xls' Excel sheet from the 'Materials on QSW' section of the class page?  When I adjust any of the three values in the yellow boxes it crashes Excel.  I am running Excel 2007 and have macros enabled.  When macros are disabled, then I can edit the cells, but the link to the auto-computation is broken and the calc doesn't work (and Excel doesn't crash).

I can get the other one (QSWspreadsheet.xls) to work.  When I change the yellow cells, the calculated values below update and all is good.

Anyone else having this problem?  Or am I missing something?  Thanks 

Active clamp forward

I'm stuck as I can't seem to get an expression for jm1 for the active clamp forward. It may or may not be necessary, as Cclamp adjusts to reset the XFR but is there a way to determine this? Also it seems that once the turns ratio is fixed and the device parasitics are fixed (by virtue of selecting a particular mosfet) all I can do is play with Lm to achieve ZVS and select this in a manner that minimizes the magnetization current. Anybody else have a different approach?

Compensating resonant converters

I had a question regarding the compensation of a resonant converter be it a resonant inverter or a half/full bridge converter that has DC output voltage or any of the ZVS/ZCS half wave or full wave QR or QSW converters that we studied in class. How do we go about compensating such converters? Is a typical PID controller enough like the one we studied in intro to Power electronics? Or is there something additional required? Any tips and references are appreciated.

HW10.3 help

All,

I'm having trouble finding the value of J to get Ro so L and C can be solved for. I have a value for JL3=sqrt(1-2u) and JL4=0 at max load for ZVS but I can't determine how to find JL1, JL2 and J. It seems I should used the eqns from problem 2 but I'm having trouble with that problem as well and can't move forward on this problem.

Thanks, Joe

HW10.2 ZVS-QSW definitions

Hi,

In the notes with definitions for D and the angles, do the graph for v2 and the state-plane diagram match with each other? The state-plane diagram starts at (-JL4, 1), while the v2 plot starts at 0V. Shouldn't the v2 plot have started at V1=Vg, like was also discussed in the lectures? Then the v2 plot would match with the state-plane diagram again I would say.
Any comments?

Toby

HW9 problem 3 help

All,

I would like to know if anyone else is getting something besides Js=1.

Here is my approach. I have an equ. ckt like the boost with a half wave ZCS QR switch from the lecture notes. The current source is the current through Lm reflected to the secondary. If Js=1, then ton will be a specific value and not a range. Any help would be appreciated.

-Joe

HW7 Prob 1 Different times for zener discharge

Hey everyone, I noticed that I get two different time values for the time period where the zener is on depending on the method I use (for P=100W case):

Method 1 (lecture 20 slide 3 method):
L_l = 16u I_p = 1.43
t_z = (16u * 1.43)/(500-300-100) = 229nano seconds

Method 2 (state plane geometry, annotation from lecture 20 slide 1, theta_p is the angle between r1 and r2):
r1 = 1.45 r2 = .25 and r2 = r1 * cos(theta_p) => theta_p = arccos (r2/r1) = 1.4 radians
w_o = sqrt (L_l * C_ds) = 25M
w*t = theta => t_z = theta_p/w_o = 1.4/25M = 59nano seconds

Why do these not match up? I used state-plane geometry to get all the other times for my graphs, but now I am doubting these values. What am I missing?

MATLAB graphing in HW7 Problem 3

Hi class,

I'm very bad at MATLAB to say the least and am having trouble graphing the equations in problem 3. We're supposed to graph similar equations to what is shown in slides 13 and 16 of Lecture 22.

Right now I am rearranging the equations as J = ........*M and then using plot(M,J)

However, it is very tedious and I am not sure my graph is correct. Is there a simpler way to graph these equations? If you could point me to some MATLAB references that would be great.

-Rob

HW7 prob 2

Hello everyone. I need some help.

Part a. Is anyone else calculating a vertical line at pi-2 for mc vs jl?

Part b. From the lecture notes gamma=2pi and J=2/pi. Here is what I've calculated for the rest. Mc1=2, Ma2=3/2, Ma1=1/2, alpha=undefined and beta=undefined. Does this sound correct? I'm assuming the sketch will be a horizontal line at J=pi/2.

Thanks for the help.
-Joe

HW5 Prob 2 Value Check

Hey everyone, just wanted to do a value check on HW5 prob2:
b) when I compute the steady state V expression @ fso= 110k, I get Vout = 23.9-j48.2
I'll skip small signal since it can't be evaluated without 's' as well as 2c's expression
d) I get Genv(0) = 27.5 this seems wrong to me.

For part d I did the following:
Genv(s) = v_hat / d_hat (Kpwm term multiplies into this but doesn't change the value)
v_hat = ((V* x v_hat) + (V x v_hat*)) / (2 x ||V||)

Last question, the 's' in the small signal voltage AM expression 's+jwso' (part b of this problem) is the update rate of the duty-cycle modulation correct?

Ugly Algebra

Is anyone getting a manageable version of ||H(jwso)||? I am at the point where I can barely fit the equation on a single sheet of paper and it's not looking good about reducing the thing much more...

Here's what I got for ||H(jwso)||:

RCwso/(sqrt((RCwso)^2 + (1-LCwso^2)^2))

Just wondering if anyone got anything would would get rid of the radical and help to reduce the massive ugliness that ensues with Genv(s).

Thanks!

The principle of modulation frequency

Hey everyone, just want to make sure I am thinking of modulation frequency, fmod, correctly. fs is the switching frequency and basically fmod is how often I am adjusting the switching frequency, is that correct? So in a real system, fmod would be fixed value, a lower value for slower output regulation, and a higher value for faster output regulation, correct?

Also, the 's' in Genv(s) is the modulation freq (s = j*2*pi*fmod), correct?

Thanks for the clarification.

HW 3 19.8c

I need some help finding fm from 19.8 c. Here is how I'm starting
Zi0(jw)=1/jwC+jwLs Ziinf(jw)=1/jwC+jw(Ls+Lp)
Zio(jw)=j*(wLs-1/wC) Ziinf(jw)=j*(w(Ls+Lp)-1/wC)

||Zio(jw)||=wLs-1/wC ||Ziinf(jw)||=w(Ls+Lp)-1/wC

When I set these two equal to each other I end up with wLs=w(Ls+Lp).
Let me know how I should approach this problem.

Question about example problem and solution

Hi,

I was working through the example problem and solution provided and came up with an inconsistency that relates to homework problem 1.

In the solution, on page 4, the denominator polynomial is shown as having two roots at

s = (-wo/2Q) +/- j(wo/2Q)..............

My problem is with the (wo/2Q) terms. After working through the problem on my own, everything seems fine, except those terms should instead be (1/(2Qwo)).

Even if you work out the problem using R's, C's, and L's, my solution would still be simplified to (1/(2Qwo)). Because the tank transfer function is the of the same form as homework problem 1, this makes a difference for the homework assignment. Can someone please confirm if the example solution is correct or if there is an error in the solution? Thank you.

Problem 19.9

Is anyone getting a Rcrit < 500 Ohms? I was going good until I hit part e and I think I may have done it all wrong..

HW3 Problem 19.6

Hi All,

I am getting started on HW 3 and have run into some confusion on the first problem. Can anyone steer me in the right direction... Here's what I was thinking: the 200 kHz that is mentioned in the problem is fs. In part a it says to derive expressions for Voc and Isc... I am assuming that Voc will be (4/pi)*Vg * H_inf(jws) and Isc = I/sqrt(1-(V/Voc)^2), where I=Vnom/Rnom and V = Vnom. The issue that I am finding is that I am not seeing how to get an F term in the expressions, any hints?

HW 2 Prob 19.4 below vs above resonance

I believe in the converter operates such that. Is this correct?

below resonance, vc(t) leads ig(t)
above resonance, vc(t) lags ig(t)

Thanks

HW 2 Prob 19.3b - sketch bode?

I'm a bit confused on the wording of the problem. 19.3b: "Sketch a Bode diagram of the parallel LC parallel tank resonant."

Isn't this the same as H(s)?

But H(s) = (sL||1/sC||Re)/(sL||1/sC||Re) = 1 given that Zo(s)=Zin(s).

If that's the case, what's the point of plotting H(s)? Or is the problem asking to plot the bode for sL||1/sC? Thanks.

HW2 19.1d

Hello everyone, I have some questions on HW2 19.1 (traveling at the moment and running behind on homework):
19.1) The effect of the transformer on the inductor seems to be kicking my fo to be in the 800kHz range which seems awfully high. Did I do something horribly wrong? For Zo I have L/400 || C || Re. I get an answer that is very close to 19.31 except with a scaling factor (for the transformer and due to the input square wave having a DC offset).

Also, when I get to part D, my fs is less than fo when I assume n=1. For n=3 I get imaginary values for F. I would have expected an fs higher than fo since that is assumed above. I also would have expected fs and fo to be very close...

thanks for your input,
charlie

Etymology of "resonant tank"?

Brief change of pace: anyone know the origins of the word "tank" as it's used in this class, and electrical engineering in general?

Wikipedia claims it's got to do with the image of water sloshing back and forth in a tank, but doesn't cite any sources, and I can't find any other clues in my brief search.

HW #2 19.1 E and G

I am having a little trouble figuring out the peak current through the transistor for 19.1 Part E.  So far my thoughts are that the peak transistor current will match the peak ig, input current, which is also the same as the peak current value through Cb. So I get something like Ig = Is1cos(phi_s)/pi and want to solve for Is1. I feel like I should relate the equation back to power, i.e. Pg = VgIg = <ps(t)>, but I don't know how to solve for the input power either without Ig. I've been circling around this for a little while, and feel like I missing some minor(?) detail. Any help is appreciated. Thanks!

in SRC (lecture 4), is phi_s = phi_r ? [i_s(t) = i_r(t)]?

SRC of lecture 4, we said: v_r(t) ~ Vr1 * sin(ws*t - phi_r) and i_r(t) = Ir1 * sin(ws*t - phi_r).
Also, we said that i_s(t) = Is1 * sin(ws*t - phi_s).
Since the resonant circuit is in series, one would think that i_s(t) = i_r(t). Then, Is1 = Ir1 and phi_s = phi_r. Is that true?
Regards,
Nitish

HW 2 Problem 19.3

I find that my equivalent circuit model for part A is identical to Figure 19.22, with a different tank network, and hence a different H(s). Because L and C are in parallel, Vc(t) (or Vs(t) depending on which figure you are looking at) equals Vr(t), making H(s) equal to one. This would then make M, which was equal to Eq. 19.27, solely equal to 8/(pi^2), which would not depend on Qe and F. Any ideas on how I am doing this so drastically wrong? Thanks

Lecture 8, 9, 10

Hello Class

Are we having the correct lecture videos for 8,9 and 10? Thanks.

Spice sim of pll res DC-DC converter lecture 5

I was trying to simulate the pll resonant DC -DC converter of lecture 5, to see if I got a square wave shape i_R(t). I noticed that i_R(t) appeared square wave like only before the steady state was reached, after which it appeared like DC. Moreover, when i_R(t) did look like a square wave, its amplitude kept slowly changing over several cycles.
I used a square wave signal gen +/5V, 100kHz
Lr = 1.591uH, Cr = 1.591uF
Lf = 20mH, Cf = 1500uF

Any comments would be appreciated.

Zero Current Switching in practice

Hi,

In the book (and also in the lectures) it is explained that ZCS occurs when (for a full bridge) Q1 and Q4 are on and the current becomes negative (below resonance, current leads voltage, see section 19.3.1). The diodes D1/D4 then automatically take over the currents of Q1/Q4 and there is ample time to turn of the switches.

The part I don't completely understand is why the diodes would take over the current. That may be the case with ideal diodes that have forward voltage Vf=0V. In practice, a threshold voltage is required to forward bias the diodes, so Vf~0.7V. Since MOSFETs are bidirectional devices, they would conduct the negative current and their Ron*Isd would have to be larger than Vf before the diode turns on and takes over (some of) the current. Now suppose Ron*Isd is smaller than Vf, the diode would not conduct and the transistor would carry all the current

For kW type converters, ZCS may be easy to achieve, since probably Ron*I>Vf. But is it also practical to use ZCS in smaller converters?

Any comments would be much appreciated.

Regards,

Toby

H(s) for 19.1

I am getting something really ugly for H(s) for the resonant tank...

I am starting with:

H(s) = Zo/((Ls/n)+ n/Cbs)

where Zo is (Ls/n + n/Cbs) || 1/Cs || Re

Did anyone approach this differently?

HW 2 Problem 19.1

There is some discussion in the 2010 posts about the sinusoidal approximation of v_s1(t) being multiplied by 1/2 because v_s(t) has a maximum value = V_g and minimum = 0, rather than the textbook example of +V_g and -V_g. A result of this scaling factor being that H(s) is also scaled. I don't think this is correct. The fundamental component of the Fourier series contains the amplitude term V_g ( (4*V_g/pi)*sin(w_s*t) ); that being the case, if V_g oscillates between V_g and 0 the sine wave will be accordingly 4*V_g/pi or 0. No need to scale. This will approximate the square wave. Does anyone else have some thoughts on this? Thanks.

HW 1 question 1

I've started looking at the HW and have viewed all the comments on the blog but am having trouble starting the HW. I don't remember solving differential equations of circuits in ECEN5797. Is there a section I could read in the book to brush up on this? Here is what I have right now. Could anyone give me a nudge in the right direction.
V-v(t)=Ldi(t)/dt and i(t)-I=Cdv(t)/dt

HW 1-1: Should V and I be considered step inputs at t=0?

HW 1-1: Should V and I be considered step inputs at t=0?
regards,
Nitish

HW-3(c)

Hi, all. For Q3(c), do you think it is assumed that Ds has the same I-V characteristics as D or not? Because if Ds is identical to D, then when D is on, Ds will shunt approximately the same amount of current as D. In that case, when Ms is on, the reverse recovery loss of Ds will be inevitable.

HW 1-1

Hi All,

It has been about 9 years since I took my circuits course and I'm struggling a little bit with this homework. I am getting i(t) and v(t) to be of the form X + Acos(wt) where X is a DC term and A is a constant. In order to find max values, I was thinking that taking the derivative and setting equal to zero is the right approach... Is this how anyone else approached the problem?

HW 1 Reverse Recovery in a boost converter

It is stated that "The diode remains forward biased... until the end of interval ta." Does this mean that all of the current through the diode during the tb interval should be considered to be stored in the diode junction and recovered during the next switching event?

HW1-1

Hi,

Regarding the HW1-1, the time domain differential equation:

I assumed the time domain function for i(t) is like I+A.exp(st) where A is a constant. I substituted this into the second order differential equation describing the i(t). However, the s values are imaginary and not including real part. It means that the i(t) is not damping. The inductor current should damp to I after long enough time. I cannot see the mistake I made in my approach. Should I assume any other solution for i(t) rather than the one mentioned above?

Would you please give me a hint on that.

Amin Z.

Welcome to Spring 2012 ECEN 2012 Blog

The purpose of this blog is to encourage and enable both on-campus and off-campus students to post questions, comments, ideas, discussions or pointers to on-line resources related to course materials and homework assignments. The instructor may use the blog to address common HW questions but will not moderate or edit the posts (except in cases of course policy violations), so you should not assume that any comments or ideas posted here by other students have been approved, verified for correctness, or endorsed by the instructor.  Course announcements, materials, solutions, etc. by the instructor will be discussed in lectures and posted on the course website.


The blog includes a history of posts from Spring 2010. Please note that the homework assignments and the schedule are subject to change, so references and comments to past homework problems may not apply.