Control-relevant identification of an ill-conditioned distillation column

Identification for control of an ill-conditioned system requires special techniques. The directionality of such a system should be taken into account in the design of identification experiments. This requires some prior information about the system. In distillation, information about the directionality properties can be obtained from certain flow gains, which are easy to determine in practice. Based on such information, the plant can be explicitly excited in its high- and low-gain directions. In the paper, a pilot-scale distillation column is identified by this approach at two different operating points. The models obtained are superior to models determined via traditional step tests. In this case, the former satisfy integral controllability requirements, while the latter do not.