Design of nonminimum phase processes for optimal switchability

Based on a method for the evaluation of switchability for nonlinear nonminimum phase processes with input multiplicity, a design method is presented that determines the optimal design with respect to switchability out of a range of possible designs. An optimal control problem formulation determines a stable approximate inverse of the process in order to evaluate the limitations that are imposed by the presence of nonminimum phase behaviour and input multiplicity on the different designs. The approach is illustrated on a case study involving the design of a system with reactor and separator. It showed that a different design is preferred for switchability between two operating points than for controllability around the basic operating point. The optimal design for controllability around a steady state is minimum phase, whereas the design for optimal switchability is nonminimum phase at both operating points. The importance of considering dynamic aspects at the design stage is illustrated with this study.