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Behaviral modelling of dc-dc voltage converters (Read 635 times)
navin_kumar
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Behaviral modelling of dc-dc voltage converters
Feb 02nd, 2006, 8:49pm
 
Hi
can any one give me good information about
behaviral modelling od dc-dc voltage converters in spectre
for top level behaviour analysis
thanks & regrds
navin
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jbdavid
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Re: Behaviral modelling of dc-dc voltage converter
Reply #1 - Feb 3rd, 2006, 12:17am
 
What kind of information do you want? yes its very feasible..
Jonathan
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navin_kumar
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Re: Behaviral modelling of dc-dc voltage converter
Reply #2 - Feb 3rd, 2006, 12:52am
 
Hi jonathan
i  want to do the stability analysis for the total current mode dc-dc voltage converter
so i want information  how  we can model all the individual blocks in the dc-dc converter with  verilog
because i  am havin spectre simulator i can model the blocks using verilog
please give me information about any good thesis or papers
thanks & regards
navin
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Jess Chen
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Re: Behaviral modelling of dc-dc voltage converter
Reply #3 - Feb 3rd, 2006, 10:16am
 
Navin,

You may want to check out the Forum discussion at

http://www.designers-guide.org/Forum/YaBB.pl?num=1123068853

I assume you meant to write VerilogA instead of Verilog since you want to use Spectre. It is possible to simulate a power supply using Verilog and I can see how you might take that route for faster simulation, especially since many parts of today's power supplies are digital. However, if you want to do stability analysis, I would use Spectre and VerilogA.

Most of the books I've seen on modeling power supplies were written for simple versions of SPICE that do not support VerilogA. I will post one later. I have not seen any books on modeling power supplies with VerilogA. Perhaps it's time for one.

Are you interested in perfomance models, functional model, or some combination? Performance models simulate gain/phase margins etc. Functional models check connectivity and assume everything is ideal.

You may also be interested in the books below.

"Fast Analytical Techniques for Electrical and Electronic Circuits" by Vatche Vorperian. Cambridge University Press. 2002.

Johnny C.  Bennett, "Practical Computer Analysis of Switch Mode Power Supplies". It's published by CRC Press.

-Jess
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navin_kumar
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Re: Behaviral modelling of dc-dc voltage converter
Reply #4 - Feb 4th, 2006, 10:23pm
 
Hi jess chan

 i mean   verilog A  only, so that i can do it by using spectre
i  have to do  the stabilityanalysis of  CURRENT MODE DC -DC VOLTAGE CONVERTER USING PWM CONTROL
can u give any information about the performance modelling of dc-dc voltage converter
how to model each block of total dc-dc voltage converter
thanks & regards
navin
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Jess Chen
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Re: Behaviral modelling of dc-dc voltage converter
Reply #5 - Feb 5th, 2006, 10:25pm
 
I could list a bunch of references for you but most of them are out of print. I think your best bet is to pick up a book like Voperian's book (listed above) and check out pages 440-459. There are other books but again, like many of the original papers, they are probably out of print. Voperian's book is fairly recent. There may be other recent books on the subject.

I do not have time to write out a detailed procedure, especially since I have not seen your schematic, but I can outline how I would attack the problem. Your analysis will most likely proceed in three steps:

1. Replace the switching elements with state space averaged models, usually DC/DC transformers. These can be easily implemented in VerilogA. If your inductor is always in continuous or discontinuous mode conduction, you can use a fairly simple model. If you want your model to be capable of switching conduction modes, your model will be more complicated. Be sure to include the input filter and any common mode EMI filters your system may have.  There is another discussion in this section of the Forum where I give a few more details on state space averaging.

2. Based on your control (current mode control in your case), derive an expression for the duty cycle in terms of the input voltage, output current, output voltage, stabilizing ramp, and error amplifier voltage. You should be able to implement the control law in VerilogA too.

3. Identify and analyze the loops of interest. Current mode control involves multiple feedback loops. If you want to break all feedback loops, split the duty cycle node. You can assess the loops one at a time as long as you leave the loops closed for the next loop and keep track of closed loop right half plane poles. This procedure is called sequential loop closures or the sequential return difference method. I can give you references on the procedure but I must warn you that they are probably fairly obscure. Another approach is to compute the closed loop poles directly using Spectre's pz analysis. However, you will definitely want to check your results. The last time I used that feature, it gave a lot of extra poles and zeros. That is why I would probably use the sequential return difference method. If you are certain  the inner loops are stable, you can leave those closed and concentrate on the outer loop, which is probably a voltage loop. In general, you should check your stability analysis against a step or impulse response. For AC stability analysis of one loop, I usually break the loop by inserting a zero voltage DC voltage source in the loop of interest, at a point where the upstream impedance (the source impedance), is much smaller than the downstream impedance (load impedance). There is a new Spectre feature called "stability analysis" that does not have such an impedance requirement. I tried it once and it seemed to work fine. However, in a multiloop system, you may have to resort to the large LC trick to break the loops that have not yet been analyzed without affecting the DC operating point.

I apologize if my response is too short but that's all I have time for right now. Please let me know what parts are unclear and I will elaborate on them later.

-Jess
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navin_kumar
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Re: Behaviral modelling of dc-dc voltage converter
Reply #6 - Feb 23rd, 2006, 4:22am
 
Hi  jess thanks for the information
one more help i need is in this implementation i need to combile both the PFM AND PWMin asingle block for improving light load efficiency can u please give me some information about the switching the mode
thanks  & regards
navin
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Jess Chen
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Re: Behaviral modelling of dc-dc voltage converter
Reply #7 - Feb 23rd, 2006, 8:24am
 
It's been several years since I've worked with power supplies and I am not familiar with the PFM acronym. As for modeling switch mode power supplies for light load, you probably need a dual-mode state space averaged model. Such a model runs very fast, is easily linearized by Spectre for AC analysis, and automatically switches between continuous and discontinuous modes. There may be more recent papers on such models but I can send you a couple of old ones if you are interested. These older papers were written for macro modeling, models built from SPICE primitives, but you may be able to convert them to VerilogA once you see how they work. However, I would recommend that you start from the state space averaging fundamentals. Look for papers by Drs. Middlebrook, Cuk, and I think, Ridley. I believe Dr. Fred Lee and/or some of his graduate students also wrote a few papers on modeling current mode converters. Once you understand the theory, implementation in VerilogA should be straightforward.

-Jess
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navin_kumar
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Re: Behaviral modelling of dc-dc voltage converter
Reply #8 - Feb 23rd, 2006, 8:42pm
 
Hi jess
thanks for the information
i  will follow as u  said and send me the links for the papers  that u have
thanks once again
navin
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Jess Chen
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Re: Behaviral modelling of dc-dc voltage converter
Reply #9 - Feb 24th, 2006, 12:08pm
 
I will e-mail you a couple of papers.

J. E. Chen and F. D. Rodriguez, "Duo-mode non-linear state space averaged SPICE model fo a current mode buck converter". Proceedings of the 1988 Applied Power Electronics Specialists Conference.

F. D. Rodriguez and J. E. Chen, "A refined nonlinear averaged model for constant frequency current mode controlled PWM converters". IEEE Transactions on Power Electronics, Vol 6, No. 4, Oct 1991.

-Jess
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richard88
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Re: Behaviral modelling of dc-dc voltage converter
Reply #10 - Mar 5th, 2006, 9:13pm
 
Jess,
 Can you comment on the differences, advantages between the PWM switch model (Voperian) and the canonical circuit model (middlebrook & erickson's book) ? If I wish to run ac sims to determine loop gain & phase, which is easier, better ?
 Is the Bennett's book talked about using switch model or canonical model ?

Thanks.

Jess Chen wrote on Feb 3rd, 2006, 10:16am:
Navin,

"Fast Analytical Techniques for Electrical and Electronic Circuits" by Vatche Vorperian. Cambridge University Press. 2002.

Johnny C.  Bennett, "Practical Computer Analysis of Switch Mode Power Supplies". It's published by CRC Press.

-Jess

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Jess Chen
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Re: Behaviral modelling of dc-dc voltage converter
Reply #11 - Mar 6th, 2006, 4:14pm
 
richard88,

Can you be more specific about the Middlebrook/Erickson book? I'd like to be sure the canonical circuit is the one I remember. Is the canonical model in the book the same one that appeared in Wester's paper, Cuk's thesis, and a couple of PESC papers in the 70s?

-Jess
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richard88
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Re: Behaviral modelling of dc-dc voltage converter
Reply #12 - Mar 6th, 2006, 5:53pm
 
Jess,
 I don't have the 70s papers, but I think the canonical form is that of the Cuk's thesis, an attachment : http://ece-www.colorado.edu/~ecen5807/course_material/introduction2005.pdf
 In Voperian's paper, he mentioned his model is more suitable for SPICE analysis. I wish to get comments on the pros and cons of each models. Particularly, which one is more commonly practise in the industry.
 I've constructed an ac model, I wonder if I can email you and get your comments on it ? If so, can I get your email id ?

Thanks.
Richard


Jess Chen wrote on Mar 6th, 2006, 4:14pm:
richard88,

Can you be more specific about the Middlebrook/Erickson book? I'd like to be sure the canonical circuit is the one I remember. Is the canonical model in the book the same one that appeared in Wester's paper, Cuk's thesis, and a couple of PESC papers in the 70s?

-Jess

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Jess Chen
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Re: Behaviral modelling of dc-dc voltage converter
Reply #13 - Mar 6th, 2006, 6:51pm
 
Richard,

Yes, you can e-mail your AC model and I'll look at it. If you log into the Forum and click on my user name, a message window will pop up with my address already filled in. But in case you have trouble with it, my address is chennanga@yahoo.com. It helps if I can see the behavioral schematic so I don't have to reconstruct it from a netlist.

-Jess

P.S. As I recall, you were trying to use PAC to do a frequency domain loop gain analysis of an un-averaged SMPS model. Such an approach would be very powerful. Did it work?
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richard88
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Re: Behaviral modelling of dc-dc voltage converter
Reply #14 - Mar 6th, 2006, 6:57pm
 
Jess,
 Thanks for your response.
 Actually I have emailed you earlier on using that email address, wonder if you have received it ? I'll email with a diagram later.
 Yes, I have used PAC to run sims, it is powerful but it has a problem ... at times, the circuit can be difficult to converge. Very often I need to play around the integration method option to get it to converge. Also, we need to reduce as many components such as D-Flip Flop or else the convergence time can be very long.

Thanks.


Jess Chen wrote on Mar 6th, 2006, 6:51pm:
Richard,

Yes, you can e-mail your AC model and I'll look at it. If you log into the Forum and click on my user name, a message window will pop up with my address already filled in. But in case you have trouble with it, my address is chennanga@yahoo.com. It helps if I can see the behavioral schematic so I don't have to reconstruct it from a netlist.

-Jess

P.S. As I recall, you were trying to use PAC to do a frequency domain loop gain analysis of an un-averaged SMPS model. Such an approach would be very powerful. Did it work?

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