Robust internal model controller with increased closed‐loop bandwidth for process control systems

Abstract

This study proposes a modified internal model control (IMC) structure in which an additional controller is added to the standard IMC structure to improve the closed-loop system bandwidth. The resulting structure is evaluated to satisfy standard IMC objectives of nominal performance and robust stability. The novelty of the work is to design a fractional order (FO) filter in the IMC structure so that gain margin ( A m ) and phase margin ( ϕ m ) specifications could be independently satisfied for a first-order plus time delay (FOPTD) process control plant. The proposed modified IMC (m-IMC) is simulated for three different FOPTD systems to validate and substantiate the theoretical analysis. The proposed m-IMC is compared with different integer order as well as FO controllers. The transient performance are compared in terms of rise time ( T r ), settling time ( T s ), maximum overshoot (% M p ) and the effectiveness is measured in terms of integral square error. To validate the viability of the proposed control scheme, it is implemented on a laboratory DC servo-system.