ON THE USE OF DIAGONAL CONTROL VERSUS DECOUPLING FOR ILL-CONDITIONED PROCESSES

We argue that ill-conditioned processes do not necessarily preclude th e use of decoupling control. This applies also if the process is ill-c onditioned in the crossover frequency range of a diagonal controller. Therefore the rule that one should never use a decoupler for ill-condi tioned plants is misleading. The investigation is based on a discussio n of the performance sensitivity of ill-conditioned systems and observ ations made from analyzing a semi-realistic model of a distillation co lumn. (C) 1997 Elsevier Science Ltd.