Youla Parameterization-Based Fractional Repetitive Control of Arbitrary Frequency Disturbance Rejections for Line-of-Sight Stabilization

This article proposes a fractional repetitive control (FRC) based on Youla parameterization to reject arbitrary disturbances up to the Nyquist frequency. This control strategy transforms disturbance rejections into the design and optimization of the FRC. The improved conjugate repetitive controller incorporates an all-pass fractional delay filter (ADFDF) to reject arbitrary aperiodic and periodic disturbances, while mitigating the waterbed effect at nonrepetitive frequencies. Furthermore, due to time delays limiting both the control bandwidth and the strength of notches in the FRC, an extra time delay factor is introduced to ensure that time delays characterize one at the specific frequency. Consequently, the arbitrary disturbances occurring within the Nyquist frequency are effectively suppressed. Simulation analyses and experimental results demonstrate that the proposed method enhances the disturbance rejection capability of the line-of-sight (LOS) stabilization system.