A new active disturbance rejection controller design based on fractional extended state observer

An improved active disturbance rejection controller based on the fractional order extended state observer (FOESO) is proposed in this paper. Applying the proposed FOESO, a second order plant model is converted into a cascaded fractional order integrator (1/s2 α, 0< α< 1). Thus, a stable closed-loop feedback control system with enough phase margin for stability can be realized using a simple proportional controller. Besides, the open-loop phase-frequency characteristic of the system is flat around the gain crossover frequency, namely, the system is robust to loop gain variation. Furthermore, without the differential action in the designed controller, the control system achieves the robustness to high-frequency noise.