How to find transfer function of switching converters??

[zuq]

I am making a DC motor speed controller,
Using half bridge chopper,
Current mode control.

I am not sure how to find transfer function of a switching converter,
I want to find the transfer function in order for me to design the appropriate compensation network for current mode control.
I am totally lost,

Please suggest something useful.

 

[umesh49]

It is not staraight forward... Derivation of those transfer function are differrent type of mathmatics called something "state space averaging". you can try searching else I will try to remember the book I refered 6 year back.

 

[zuq]

Hi
Thanks for your resPonse,
Yes i have a book on state space averaging by Erickson.
It seems extremly complex maths and I was hoping if there was an easier way of doing it.
Or should I spend the time and derive all the equations???
Maths isnt my best subject so ya....
What do u suggest?

 

[umesh49]

I woud suggest to go for some simulation tool, and tweak with parameters to achieve the performance. That how it is done in industry.

 

[zuq]

THanks Umesh

Do u recommend any software?? I am a university student. Is there any freeware available? I tried looking online, I found one from Psim but it is rather expensive, $2500.
I will only be using it once for my final year project so probably not worth buying.

 

[umesh49]

You could find some free ware tool like pspice/ multisim. I did not really use them so not sure how much it could be helpful.
You can try doing in Matlab if you have in your university.
Have a look a below threads for simulation tool discussion.

https://www.edaboard.com/threads/200930/

 

[atripathi]

You can do this in PSpice. Read more about it and download evaluation version from **broken link removed**

Simplest way to model switching convertor is use error amplifier with compensation network, GAIN block (ratio of voltage at control pin to O/P DC) followed by filter.
Hope this help.