Re: poles and zeros
You are talking about a topic called power electronics system modeling. Transfer function ca be obtained in easy way for a Buck converter, basically the transfer function is the same as the RLC resonant circuit used as low pass filter for the square wave of PWM generation. Other topologies, as Boost converter, require more subtle modeling process and you can find it in the excelent book Power Electronics: Converters, Applications, and Design by Mohan
In this book you will find detailed models for each common topology. Another pretty book with this topic is Eriksson´s fundamentals of power electronics.
When you get the basic learning of the models, yo should use the tool power system blockset of matlab for simulation of these models. Compare the circuits models with inductance, capacitante resistance and transistor with their linear system conterpart.