Boost converter small signal model error

Thread Starter

AMANORA

Joined Sep 21, 2021
9
So I was simulating a boost converter on plecs, wanted to calculate Gvd. Firstly I solved the model by hand and drew the bode plot, then I drew the schematic on plecs, made sure of the values and parameters are equal to what I designed by hand. my issue is that my dc gain that I calculated by hand is twice that got drawn by plecs. I made sure of my calculations by referring to this to make sure that I made no mistake. my calculations are equal to the model presented here.
Post image
Model
this is the schematic on plecs. D = 0.5

Post image
Schematic
This is the average Dc output voltage.
Post image
And this is the bode plot of the converter.
Post image
Gvd
As you can see, the dc gain is about Vinput/(1-D), instead of Voutput/(1-D).
I really hope that this is not a dumb question and itsnot a silly mistake of mine since I spent too much time working and searching what did I do wrong :S.
Thanks :)
 

Irving

Joined Jan 30, 2016
2,196
Your FET is drawn upside down....

Here's the LTSpice equivalent, D = 0.5, f=100kHz
I'm not sure how you're generating your bode plot

1632232367343.png

Close up of 1 cycle @ steady-state
1632233011462.png
 

Thread Starter

AMANORA

Joined Sep 21, 2021
9
Your FET is drawn upside down....

Here's the LTSpice equivalent, D = 0.5, f=100kHz
I'm not sure how you're generating your bode plot

View attachment 248491

Close up of 1 cycle @ steady-state
View attachment 248493
Hello Sir, thanks for replying and I hope I am not wasting your time.
Plecs has an intrinsic small signal model generator analysis. My time domain analysis lies inline with my hand written calculations, but the bode plots are not..
I tried another schematic which is already drawn in my book, the issue is always the Gd0 or the low frequency gain, its always lower that whats expected to be.
Again thanks for your time :).
 

Irving

Joined Jan 30, 2016
2,196
Understood, LTSpice also has a small signal analysis capability. Confusingly you talk about DC gain but a Bode plot is an AC analysis. So what are your input and output signals?
 

Hughes4

Joined Sep 22, 2021
1
Pleased to see your question as I think I have the same question, I am also confused and in need of light on this same issue. Need help.

<Mod: link deleted.E>
 
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Thread Starter

AMANORA

Joined Sep 21, 2021
9
Understood, LTSpice also has a small signal analysis capability. Confusingly you talk about DC gain but a Bode plot is an AC analysis. So what are your input and output signals?
Hi, sorry for the confusion, I meant with the dc gain is that low frequencies gain, its written in books as Gd0. I just fixed it and it was a pwm issue. Thanks for yout time :)
 

Thread Starter

AMANORA

Joined Sep 21, 2021
9
Pleased to see your question as I think I have the same question, I am also confused and in need of light on this same issue. Need help.

<Mod: link deleted.E>
Hi budd, can you please email me at <Mod: Deleted email address, avoid Spam.E>
 

Irving

Joined Jan 30, 2016
2,196
Hi, sorry for the confusion, I meant with the dc gain is that low frequencies gain, its written in books as Gd0. I just fixed it and it was a pwm issue. Thanks for yout time :)
No problem.

BTW, that other message was an advertising Bot, not a real person...
 
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