Three-degree-of-freedom internal model control for unstable process

A new design algorithm of three degree of freedom (3DOF) internal model control (IMC) for unstable process is presented in this paper. A robust compensator is introduced into the system to improve the robustness and the compensator in feedback loop not only can be used to stabilize the unstable process, but also for disturbance rejection. Followed the presented criterion for robust stability, the design technique is demonstrated by a numerical simulation example to give its practicability in industrial control applications.