Robust Fixed-Time Sliding Mode Control for DC/DC Converters With Varying Exponential Coefficient

In this paper, a novel disturbance observer-based sliding mode control scheme with fixed-time convergence mechanism is proposed to regulate the output voltage of dc-dc buck converters. Firstly, to assure that the convergence time of the voltage tracking process is independent of the initial state, a new varying exponential coefficient fixed-time sliding mode controller (VECFxTSMC) is proposed in the outer loop of dc-dc buck converters. The designed varying exponential coefficient increases when the system trajectory is distant from the origin to improve the convergence speed and decreases when the system trajectory is near the origin to assure the robustness. Compared with conventional fixed-time sliding mode controllers (FxTSMC), the proposed one not only assures a fixed-time convergence of system trajectory but also further enhances the robustness and dynamic performance of the system without increasing chattering, thus the performance of buck converters can be further enhanced. Then, a fixed-time disturbance observer (FxTDO) is designed in combination with the proposed VECFxTSMC to estimate the unknown lumped disturbances and enhance the disturbance rejection ability of buck converters. Finally, a set of comparative experiments between conventional methods and the proposed method are implemented based on dc-dc buck converters, and the experimental results verify the effectiveness and superiority of the proposed strategy.