Robust Predictive Disturbance Observer-Based Repetitive Control for Time-Delay Systems With Application to CVCF Inverters

This article presents a composite repetitive control (RC) approach for time-delay systems subjected to mismatched disturbances via a predictive disturbance observer (PDO). The RC framework consists of an inner positive feedback loop and an outer feedback loop. In the inner loop, the internal model of the periodic reference is constructed by taking advantage of the system model and the inherent time-delay. In the outer loop, a straightforward controller is designed to stabilize the closed-loop system. Fluctuations in time-delay and model uncertainties would introduce disturbances in the proposed internal model, which may include both periodic and aperiodic components. To address this issue, a novel PDO is introduced in the internal model to estimate these disturbances. As a result, a robust control scheme for periodic reference tracking can be achieved in the presence of time-delay, named PDO-RC. This newly proposed method can simultaneously ensure tracking accuracy and disturbance attenuation, as demonstrated by rigorous mathematical analysis. Finally, the proposed control scheme is applied to regulate the output voltage of a constant-voltage constant-frequency (CVCF) pulse-width-modulation (PWM) dc-ac inverter. Experimental results showthat the proposed method achieves smaller voltage distortion and lower total harmonic distortion (THD) compared to RC and proportional resonant differential (PRD) control.