Stabilization and Control of Unstable Processes with Large Dead Time

A control scheme is presented to achieve stabilization, satisfactory dynamic and steady state control performance for a general unstable process with dead time, where the rational function part of the process could be of non first order and the dead time of it larger than the upper bound for stabilization by PID control. The idea is to remove the stable lag part of the process by an internal model control (IMC)-like compensation with intended preservation of internal stabilizability so that the compensated plant becomes a minimal order one with unstable poles only (the first order in most realistic cases) and its internal stabilization and effective control can be carried out much easier than that for the original process. The proposed scheme can thus overcome the limitations due to presence of stable lag terms inherent in almost any process on its stabilization and effective control.