On Robust Control System Design for Plants with Recycle

A direct procedure for deriving the component transfer functions in plants with recycle when mechanistic procedure is used in the mathematical modeling is demonstrated. Multi-loop feedback controllers are then designed for the plants with recycle incorporating recycle compensator and without recycle compensator using internal model control (IMC) parameterization. In general, it is found that controllers parameterized using the recycle compensated plant model result in closed-loop systems with better nominal and robust performance characteristics when implemented on the uncompensated plant model than when its controller is parameterized using the uncompensated plant model. Furthermore, recycle compensated plants result in overall best closed-loop systems when their feedback controllers are parameterized using the compensated plant model.