Constraint Control of Recycle Systems with Input Multiplicities

Recycle systems exhibit steady state input multiplicities due to interactions of the units, even though individual units are quite simple. When handling constraints, if prospective constraint variables show such nonlinearity, control problems may arise because the steady state gain changes its sign. Using the reactor/separator system with two material recycles as a process example, a robust constraint handling controller is designed by confining the input into the large gain directions. Such directions are obtained as the Pareto optimal front of the multi-objective optimization problem which minimizes energy consumption in each unit. Performance of the designed controller is demonstrated through simulations.