Active disturbance rejection control with fractional-order model-aided extended state observer

Increasing the observer bandwidth of the extended state observer (ESO) can significantly enhance the disturbance rejection performance of the active disturbance rejection control (ADRC). However, a large observer bandwidth can also amplify the noise and degrade the control quality. This study proposes a novel fractional-order ADRC (FOADRC) approach. A fractional-order model-aided extended state observer (FOMESO) is designed by leveraging available plant information. Under a given observer bandwidth, the disturbance estimation performance of FOMESO is improved, while noise sensitivity is not aggravated. Additionally, FOMESO transforms a typical second-order plant into a fractional-order double-integrator model, reducing the phase lag to below 180∘. Consequently, the derivative component, which is sensitive to noise, is unnecessary in the feedback controller. Simulation and comprehensive comparisons demonstrate that the proposed FOADRC scheme outperforms the traditional ADRC in tracking, noise sensitivity, disturbance rejection, and stability. Furthermore, the proposed FOADRC approach is robust to plant parameter variations. The proposed method is validated through experiments on a permanent magnet synchronous motor speed servo system, confirming its superiority and effectiveness.