Unable to view lectures

Anyone else having issues viewing lectures in cuengineeringonline. I have been unable to since this morning.

Gvd of full bridge

To find the Gvd of a full bridge: In a full bridge if the primary switches at fsw then the inductor sees 2fsw due to the center tapped secondary. So to fing the Gvd can we average the currents and voltage of C and L from 0 to Tsw/2 as from Tsw/2 to Tsw they are repeated?

Will this work? If it does it can be applied to a push pull converter and half bridge too, correct?

Proximity effect

Can we have a situation where m is less than 1? Certainly seems so from the geometry and MMF graph.

Extra Proximity Loss Problem in HW 12

For the extra proximity loss problem in HW 12 for part b, isn't the proximity loss a function of φ as well as p? The added loss for each layer due to the proximity effect is φ *Q, and we can easily calculate Q, so it seems it should be a function of φ as well, unless we just assume it is something real high like 10.

HW12 Q13.6

Was anyone able to find the core loss in part a of Q13.6. I couldn't find a ur value in Appendix D to find the primary inductance in order to find delta B.

Any tips?

Problem 13.10

Wow, I am surprised that the total relative loss due to the proximity effect is nearly 100! That last secondary layer, at least in my calculations, really takes a beating.

Equation 13.71

Has anyone been able to figure out how equation 13.71 was derived?

December 9th and not November 9th

(11/19) Homework 12 is due in class (for on-campus students) on Friday, December 2. Off-campus students are strongly encouraged to follow the on-campus due date, but have a one-week grace period, which ends Friday, November 9, 5pm Mountain time.

I assume the grace period actually ends December 9th, not November 9th. :)

HW 13.4e

I'm having a difficult time finding the correct approach for part e) of 13.4. I made a Thevenin equivalent circuit for both the v1 and v2 ports from the model in part c), but I quickly get mired in a bunch of algebra. Did anyone else use this same approach?

Lecture 34 on magnetics

Can anyone post the link to lecture 34 (the one on intro to magnetics that was pre-recorded from last year). I can't seem to find it on the list.

Problem 13.5

Very curious. I am getting 1000's of amperes for the MMF source for the permanent magnet. This sounds wrong but may be an indication of how powerful magents can be. Any one else getting 1000's of amperes?

HW 9

Problem 8.15: Is anyone else finding that this algebra-on-the-graph problem is just a little more complicated than the examples from the book and lecture? Or am I actually sleeping right now, having another school nightmare? (Watch out, Chucky is learking just around the corner...)

Some useful articles on Right-Half Plane Zero

In doing some additional research on Bode plots, phase lead/lag, etc. I found the following articles and thought they were good enough to share for anyone else who is interested.

http://cbasso.pagesperso-orange.fr/Downloads/Papers/RHPZ,%20a%20two%20way%20control%20path.pdf

http://www.accessengineeringlibrary.com/mghpdf/0071776311_ar058.pdf

http://www.innovatia.com/Design_Center/Frequency_Response.htm

Problem 8.3a

For 8.3a, is the low frequency asymptote just zero or is a constant times s? I am scratching my head on this one. The gain goes to zero as the frequency goes to zero so I can argue that zero is the asymptote (the value at zero) but the gain does not flatten out as is approaches zero. There is an asymptote at +20 dB/decade which is jsut a constant times s.

What are others thinking?

Problem 6.6

For problem 6.6 do you need an input port equation, or just equations for v1 and vd3?

efficiency calculations

In some examples efficiency is calculated by

Pout / Pin

and in other places it has been calculated as

Pout / (Pout + Ploss)

How do we know which one we should use?

sample midterms

What is the password for the sample midterms?

HW 6 6.6 CCM

Is it safe to assume we are solving the problem in CCM or do we need to do a more general case?

HW 6 Problem 6.8

Was anyone able to figure out how to solve this without knowing Vg? It seems that everything (primary winding voltage, zener voltage, output voltage, etc.) need to be referenced to the input voltage.

HW #5 PFM Problem

Can someone shed some light on how they went about solving this problem? I have been staring at this for a while now and am stuck after doing the normal equations that were taught during the lectures. Any pointers would be greatly appreciated. Thanks.

Troubles with posting comments on this blog

Looks like the problems with posting comments on this blog have been related to the browser. Specifically, Internet Explorer 9 seems to be incompatible with a particular way commenting was set up. I have not been using IE for long time, which is why I could not reproduce the problem. I have changed the commenting set up and have posted a comment from IE9 successfully. Please give the blog another try and let me know if you are still having problems.

HW #5: Buck Converter with PFM

For the switching frequency expression I got a result that was proportional to the output current and included the conversion ratio M (=V/Vg) and the peak current, but did not have any terms for the inductance (which is part of the peak current equation) or output voltage (which is part of the conversion ratio M). The expression I have makes sense in that the frequency moves in the right direction as load, on time (t1), peak current, and conversion ratio are varied.

Anyone else getting the same thing? I ask because the problem statement asks for an expression of freqeuncy with L and V but these all got swallowed up in other terms in my result.

HW4 buck-boost efficiency

Anyone else made it to part e) of the buck-boost problem in HW4?

I get mired in ugly algebra when trying to calculate the efficiency or M(D) of the full buck-boost (including switching loss) analytically. I can come up with an expression that only has D, D', V, Vg, and the given constants, but it's so big I'm afraid I've missed a good simplifying assumption.

I've tried making some approximations to get rid of the ugliest bits, but want to be sure I'm not missing a key piece here.

Q2.9 from HW1

Hi can anyone please tell me why delta_IL2= VgDTs/(2L) from the HW solution.

It's a buck converter so delta_I= (Vg-V)DTs/(2L)

Can anyone please explain the difference?

HW 4 Buck Boost Diagram Error

Note that there is a mistake in the schematic diagram of the non-inverting buck-boost converter: Q4 is reversed.

The drain of Q4 must be attached to the output capacitor and the source of Q4 attached to the junction of the inductor and drain of Q3. Otherwise, when Q3 turns on the output capacitor will discharge through the body diode of Q4.

Side note: in this configuration the converter is symmetrical about the inductor and can transfer power in either direction. This is useful with a battery where the battery can be charged with a voltage source higher or lower than the battery voltage and then the converter can transfer power from the battery back to the source.

Couple questions on HW4

For the Buck-Boost problem, when we solve for the buck or boost part, does that mean we just choose one to work out? Seems like "buck or boost" is two different cases, so I'm confused why the problem keeps saying we need to solve 2 cases instead of 3.

For parts b) and c) I am essentially just using the two examples the professor showed in lecture 11, except for part b) where the problem statement states that Q2 is initially on, meaning the inductor current of Q1 will be multiplied by D prime, and not D. When I go to solve it in part d) though this doesn't line up for the transformer since the other side of the transformer is of the form D*Vg. Can we just arbitrarily sketch our waveforms such that the duty cycle lines up with what we need?

Also, why don't we include the reverse recovery of the body diodes of Q1 and Q4 when the cycle is transitioning between Q1 to Q2 and Q4 to Q3?

Thanks

Estimate capacitor ripple voltage

Any idea why while estimating cap. ripple voltage, we cannot use the technique for 2 poles i.e. using the charge in and out of cap to find dV.

Isn't it assumed (by definition of capacitor) that only the ripple current flows int he cap and the steady state current is taken by the load? Why does this method produce a different result like in HW1, first question (Q2.2 I think, it a buck-boost), part iii.

Thanks.

ECEN 5797 Study Group

Would anybody be interested in starting a ECEN 5797 distance study group?

HW3

Heads up! Homework 3 looks like a lot of work!

Bob White

HW1

In Q2.9 part d, is anyone having a problem determining the L1 ripple current. I get a term that has (Vg-Vc1) which yields zero.

Any tips?

HW 1

For the extra credit problem, I found the following link to be a helpful review of Laplace transforms as applied to circuit analysis:
http://claymore.engineer.gvsu.edu/~jackh/books/model/chapters/laplace.pdf

- Keith

Test post

Blog Test

Hey guys,

Im just testing out this new blog for Intro to Power with Dragan Maksimovic. I think this class will be tough so I am expecting to be on here quite often.

Peter B.

Recommended Reading

I am starting a topic for us to recommend papers, articles, books, presentations or whatever that would be of interest to the people taking this course.

I will start by recommending a very early and seminal paper on dc-dc converters:

Basic Considerations For DC-DC Converter Networks

E. T. Moore and T. G. Wilson
IEEE Transactions On Magnetics
vol MAG-2, No. 3
September, 1966
Pages 620-624


And if you want to see the formal proofs of many of the assertions
in this paper, look up Dan Wolaver's MIT Ph.D. thesis from a
few years later. It is tough reading that uses graph theory to
prove some very fundamental points on switched mode power
conversion.

Cheers,
Bob White

Welcome to Fall 2011 ECEN4797/5797 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 will not moderate or edit the blogs (except in cases of course policy violations), so you should not assume that any comments or ideas posted here 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, not on this blog.