Model Reference Based Tuning for Fractional-Order 2-DoF PI Controllers with a Robustness Consideration

Abstract

The paper proposes the tuning of a two-degree-of-freedom (2-DoF) fractional-order PI (FOPI2) controller based on the Model Reference Robust Tuning (MoReRT) methodology presented by Alfaro and Vilanova (2012, 2016). The tuning rules are optimized for a first order plus dead time (FOPDT) model and for an over-damped servo and regulatory closed-loop target responses. Moreover, the design takes into account a robustness consideration, expressed as a maximum sensitivity target value of 2.0, dealing with the performance/robustness trade-off of the closed-loop control system. A set of controller tuning equations (four parameters) is provided for FOPDT models with normalized dead-times from 0.1 to 2.0. Also, an evaluation of the control system performance and robustness is presented, in order to show the effectiveness of the proposed tuning method, that is compared with other tuning rules.