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Design >> High-Power Design >> Small signal current-mode PWM converter model
https://designers-guide.org/forum/YaBB.pl?num=1190012177

Message started by Monkeybad on Sep 16^th, 2007, 11:56pm

Title: Small signal current-mode PWM converter model
Post by Monkeybad on Sep 16^th, 2007, 11:56pm

Hi, all! Have a nice day!
I'm a rookie in designing power-switching converter. My circuit simulation tool is HSPICE and MATLAB.
I'm designing current-mode PWM boost and buck converters for driving the white light LED.
In my thought, the PWM converter is like PLL. I need a small signal model to predict the AC response.
So I can see the phase margin and design a proper compensating network.

Is there anyone can show how to derive the small signal model for current-mode PWM converter?
Or how you to design this circuit?
Thanks very much!

BEST REGARDS

Title: Re: Small signal current-mode PWM converter model
Post by Matthieu on Sep 17^th, 2007, 10:18am

Hi Monkeybad,

You can use State space averaged model. You can find information about this in previous post in that forum.
Maybe the following paper will interest you:
"A refined Nonlinear Model for constant Frequency Current Mode Controlled PWM converters".

However if your simulator is able to handle Periodic Steady state analysis (I know spectre RF does , don't know for the other ones), you will save time by:
-> Getting the AC response of your circuit from the schematic.
-> Being able to check for stablity issues (in small signal).

I have never used State space averaged model so maybe it is not the good reference to start but I have read it works well

Regards

Matthieu

Title: Re: Small signal current-mode PWM converter model
Post by Monkeybad on Sep 19^th, 2007, 2:20am

Thanks! Matthieu
Sorry I don't have other simulator but only HSIPCE. I think it couldn't handle the Periodic Steady state analysis.
I have read many papers about the small signal model of PWM.

R.B. Ridley, "A new continuous time model for current mode control"
V. Vorpérian, "Simplified Analysis of PWM Converters Using the Model of the PWM Switch: Parts I and II"

I follow the method of the paper to derive the model but still can't get the correct form. :(

I referred the datasheet of NATIONAL SEMICONDUCTOR LM3430.
It said the transfer function is

Vo/Vc=Gps=Aps*(1+s/Wzesr)*(1-s/WRHP)/[(1+s/WLEP)*(1+s/(Qn*Wn)+S^2/Wn^2)]

Vo: output voltage; Vc: control voltage
Aps: DC gain
Wzer: system esr Zero
WRHP: right half plane Zero
WLEP: low frequency pole
Qn: current sampling double pole quality factor

Anyone can show how to derive this transfer function?
Or what papers or data should I refer to?
Thanks a lot!

BEST REGARDS