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

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.