Active Disturbance Rejection Fractional-Order Independent Control of Time Delay Systems With Application to Air Floating Motion Platform

This article proposes an active disturbance rejection fractional-order controller (ADRFOC) consisting of a fractional-order controller (FOC) and a model-based extended state observer (MESO) for time delay systems, aiming to achieve independent control in terms of servo and regulation. The MESO with model information is employed to estimate and compensate total disturbance, and the FOC achieves optimal tracking performance, which is generated by the Bode’s ideal transfer function plus time delay (BITFPTD). The independent control is verified through mathematical derivation for the proposed active disturbance rejection fractional-order control system, and breaks the inherent servo/regulation trade-off of the proportional-integral–derivative (PID) control system. A systematic analysis design method for the FOC is proposed to satisfy the given frequency-domain specifications and a novel frequency-domain analysis method is clearly exposed to reveal how the external disturbance and measurement noise affect the estimation performance of MESO and dynamic performance of closed-loop system. Experimental validation applied on the air floating motion platform is performed to demonstrate the proposed ADRFOC achieves independent control, and is superior to the typical time-delay ADRC (TD-ADRC) and Skogestad’s internal model control-based PID (SIMC-PID) controller in terms of speed tracking, load disturbance rejection, and robustness to plant parameter variations.