This paper presents the state space modeling approach of DC-DC Buck converter. The main aim of this work is, by considering the buck converter system of Ericsson BMR450 with the PID, Polynomial and PD controllers at feedback loop, thus running a MATLAB file with an appropriate simu-link block diagram, and comparing the three controller's performance by verifying their appropriate output graphs. The third order controller design is complicated and slow in response. The second order design is simple and gives better responses than third order Polynomial, PID and PD controllers.