A Set-point Filter Type 2DOF Fractional Order PID Control System Design Scheme for Improved Disturbance Rejection Control

Abstract

Many works have revealed that non-integer order dynamics is a better representation of real-world systems compared to integer order dynamics. Then, fractional-order modeling and control has become a major topic of control system researches during last two decades. To benefit contributions of fractional-order dynamics in controller response, fractional-order PID (FOPID) controllers have been considered as a substitute of conventional PID controllers and many study reported the control performance improvements provided by FOPIDs. Later, performance of closed loop FOPID control systems can be further improved by additional blocks. This study presents a 2DOF FOPID control system design scheme involving a set-point filter for improved disturbance rejection and set-point control performance. This design scheme performs tuning of a FOPID controller and a first order pre-filter function as a set-point filter. Here, the pre-filter function is employed to deal with a design tradeoff appearing between disturbance rejection performance and step control performance. Coefficients of FOPID controller and the pre-filter are concurrently adjusted by a modified random search algorithm to find out an optimal set-point filter type 2DOF FOPID design that can provide an improved step performance with a higher disturbance rejection. Illustrative examples are presented to demonstrate results of the proposed metaheuristic design schema.