Adaptive Output Voltage Regulation for DC-DC Converters Under Non-Ideal Load Conditions: A Current-Constrained Fixed-Time Control Approach

In this article, a composite current-constrained fixed-time control approach is proposed based on the adaptive fixed-time disturbance observer (AFTDO) for DC-DC converters of hybrid energy storage systems HESS to regulate the bus voltage so that its desired reference is tracked within a fixed time. As mismatched disturbances can severely impact the system control effect, AFTDO is designed to provide the disturbance estimation and mitigate parameter uncertainties and load disturbances, which accelerates the estimation rate and enhances system robustness. A current-constrained fixed-time controller is then proposed to regulate the duty ratio such that the HESS possesses fixed-time convergence and achieves desired voltage tracking within a fixed time independent of initial states, where a current constraint gain is developed to strictly guarantee over-current protection. Moreover, a fixed-time load estimator (FTLE) is presented to enhance system robustness against external unknown loads. The closed-loop HESS fixed-time stability is rigorously proven based on the Lyapunov theory. A 420-V/3-kW scaled-down hardware platform is implemented to validate the proposed controller. Simulation and experimental results demonstrate the feasibility and superiority of the proposed approach under various fluctuating conditions.