Quantitative Analysis of Influences of Model Plant Mismatch on Control Loop Behavior

There is normally a mismatch between the current model of the plant and the model that was used for design. This mismatch is normally acceptable when the controller is designed. But if the process dynamics changes, the mismatch may be so large that the control behavior degrades and may be unacceptable. This paper evaluates the influences of model plant mismatch on the control loop behavior quantitatively. A novel method is developed to calculate proposed performance and robustness indices based on the controller and the mismatch. Priorities for maintenance can be made using these indices. Case studies demonstrate the efficacy of the methodology. In addition, the effects of different process dynamics are studied by general analysis.