A Fractional-Order ADRC With Improved Robustness to Plant Gain Variations

This article proposes a fractional-order active disturbance rejection control (ADRC) scheme to enhance robustness against plant gain variations. The scheme integrates a model-aided extended state observer (MESO) and a fractional-order feedback controller. The MESO ensures equivalence to an ideal double-integrator model, while the fractional-order feedback controller, designed based on Bode’s ideal transfer function (BITF), achieves robust performance in the face of plant gain variations. An analytical synthesis method is introduced to ensure that the open-loop system maintains an approximate BITF characteristic near the gain crossover frequency, resulting in a consistent phase margin despite changes in plant gain. Simulation analysis on two different systems demonstrates improved robustness to plant parameter uncertainties using the proposed scheme and tuning method. Extensive experiments conducted on a permanent magnet synchronous motor (PMSM) speed servo system further validate the effectiveness of the proposed scheme, showing significantly enhanced robustness to plant gain variations compared with other control methods. Additionally, the scheme provides superior reference tracking and disturbance rejection performance.