Study on nonminimum phase behaviour and optimal operation

This paper addresses the question of the relationship between input multiplicity and nonminimum phase behaviour and between controllability and optimal operation for nonlinear SISO systems. The terms input multiplicity and nonminimum phase behaviour and the implications of these features for process controllability are briefly discussed. The impact of different optimisation objectives on the controllability of the resulting operating point are demonstrated for a van de Vusse reactor. It is shown that the optimisation of the operating profit rather than the yield assures operation in the minimum phase region. The maximum operating profit is positive only in the minimum phase region. The input of zero maximum operating profit coincides with the input giving maximum yield and with the input at which the zero crosses the axis towards the nonminimum phase region. The result is generalised for systems with similar characteristics.