Design and Stability Analysis of a Discrete-time Sliding Mode Control for a Synchronous DC-DC Buck Converter

This paper presents the design, analysis, and verification of a new scheme of digital sliding mode control (DSMC) for output voltage control of synchronous dc-dc buck converter to achieve fast transient response and high robustness under wide parameters variations. In this article, two different control laws are proposed for controlling the switches. First, a control law, without considering the disturbance item in the dynamic equation of the synchronous buck converter system, is obtained in the state space model and its stability analysis is presented. Then, in order to improve the dynamic performance of the buck converter, in the case of load and line changes, another control law, with considering the disturbance item is obtained and analyzed. In fact, we designed a control law that closed-loop system has strong robustness against matched or unmatched uncertainties as it reduced chattering, steady state error, overshoot and undershoot of output voltage. Its implementation only needs output error voltage measurement and doesn't need current measurement. The simulation results are obtained using the MAT-LAB/SIMULINK software. Simulation results show that the proposed DSMC in the presence of a disturbances model is superior to proposed DSMC without disturbances consideration during immediate load and line voltage variations. In other words, it exhibits considerable reduction in terms of the overshoot and undershoot of output voltage response through an optimal control law during load changes. The proposed method almost overcomes the steady-state error and reduces the chattering to about 0.8%. Also, the overshoot and undershoot values are 4.8% and 3.9%, respectively.