Design and experimental implementation of a new robust observer-based nonlinear controller for DC-DC buck converters

DC-DC buck converters are extensively used in many industrial and end-user applications where significant attention highlights their power-conversion efficiency and robustness to load and source disturbances. This paper considers the problem of DC-DC buck converter control for Maximum Power Point (MPP) and voltage trajectory tracking applications in renewable energy systems. A new nonlinear robust controller is proposed for fast and robust output voltage tracking in the DC bus of the power source. New states are augmented in the design of a novel composite sliding mode controller. Furthermore, a nonlinear state observer is incorporated in the design for current estimation. Parameters of the overall approach are tuned using Particle Swarm Optimization (PSO) algorithm with an objective to ensure a good balance between fast transients, robustness, and dynamic performance in practical implementations. This novel strategy is cost-efficient and accounts for the switched and nonlinear aspects of the problem in addition to disturbances. The stability of the closed-loop system is analyzed and guaranteed through Lyapunov stability theory. The low complexity of the presented controller grants it a remarkable advantage for higher reliability in physical realization. Moreover, comparative simulation tests and experimental results from multiple scenarios show significant trajectory-tracking improvements in terms of faster convergence rate with short transients and effective disturbance rejection performance compared to the optimally tuned Proportional Integral (PI) controller that is widely adopted in industrial applications.