A discrete-time internal model-based ∞ controller and its application to a binary distillation column

Explicit state-space formulae for an 7-/°¢ two degrees-of-freedom (2-DOF) Internal Model Control (IMC)- based controller are derived. The IMC controller solves a special 7-/°~ control problem directly in discretetime, providing robust stability against coprime factor uncertainty, and a degree of robust performance in the sense of making the closed-loop system match a pre-specified reference model. The IMC controller structure is shown to comprise a plant state observer, an on-line step response model, and a generalised state-feedback law associated with the plant and model states. A design for a binary (methanol/water) distillation column is presented as an illustrative example.