Until now, only the PID has been used to control DC/DC converters for a Nanosatellite’s Electrical Power System (EPS), thus, the goal of this work is to investigate the feasibility of other methods. This paper focuses on a comparative study of SMC and LQR for the regulation of a Buck converter used in EPS. A study is done to evaluate their efficiency, using MATLAB/Simulink, in response to various fluctuations in voltage source, reference voltage and resistive load. To estimate the system’s states and filter the noise in the measurements, a Kalman filter is utilized. In terms of recovery time, settling time and under/overshoots, SMC outperforms the other controllers, however, the control input suffers from the chattering effect and high magnitude peaks. The SMC recovery time to a change in the load is 0.677ms, while LQR takes 1.583ms to recover. PID, on the other hand, is slower with a recovery time of 3.068ms. SMC also presents the lowest steady state error which is less than 0.01%, whereas LQR and PID have an error less than 0.36% and 0.56%, respectively.