compensation goes around the error amp, from FB terminal (- input of amp) to output. voltage mode needs two zeros. easiest way to do this is to put a capacitor across the TOP FB resistor to give one zero, then to use a series RC around the op amp to give the other zero. it's also common to put a very tiny cap (about 1/10 the series value) across the RC pair to give a high pole so your gain does not peak up at high frequency.
i would suggest you get the abraham pressman book, or the erickson book for the full analysis.
in the volatge mode dc/dc for buck . you need do compensation . becasue L.C is phase shift , you need to compensation to improve the total system phase margin . You can use type II or Type III compesation method
Using type II or Type III compesation method is the common way ,
But the compensation network will be a little large, especially when the output LC is large.
So I think the method from abraham pressman book is only for
discret design , not for IC design, anyone has better way ?