A comprehensive review of modified Internal Model Control (IMC) structures and their filters for unstable processes

This paper reviews the evolution of Internal Model Control (IMC) techniques developed so far for unstable processes. The IMC strategy has shown significant results over the past two decades, including recent inclusions of fractional-order approaches. After a comprehensive study of various methods, the critical tuning methods and structural changes are clearly accumulated with their significance and limitation concerning controlling unstable time-delay systems. The comparisons with main structural changes and filter designs are also included in the numerical study and in discussion. Finally, the key research gaps and future motivations are indicated in the IMC approaches, considering available methods in the literature.