New LADRC scheme for fractional-order systems

Abstract

Active Disturbance Rejection Control (ADRC) is a very promising recent concept for the design of controllers to control systems with uncertainties. Based on an extended state observer, this control structure allows both external disturbances and modeling uncertainties to be actively rejected. The use of the active rejection control of disturbances is gaining more and more interest among the system control community. This is mainly due to its easy design, undemanding implementation and robustness. In this paper, three solutions using the ARDC structure to control fractional-order system are discussed. Two methods taken from the literature are briefly introduced, namely, the fractional-order dynamics rejection scheme (FODRS) and the fractional linear active disturbance rejection control (FLADRC). The basic ideas and technical formulations of these two are presented. A third method, based on the robustness performance introduced by fractional-order controllers, is also proposed in this paper. The proposed design method of the set-point tracking controller is based on the Bode’s ideal transfer function (Bode’s ITF). This will improve the robustness of the control scheme.

Keywords

• Fractional calculus
• Caputo’s fractional-order operator
• Fractional-order systems
• Linear active disturbance rejection control
• Pole placement
• Bode’ideal transfer function