Sensitivity of MIMO Controller Performance to Model-Plant Mismatch, with Applications to Paper Machine Control

Model-based controllers based on incorrect estimates of the true plant behaviour can be expected to perform badly. This work quantifies the performance deterioration for a certain class of MIMO systems. Performance is measured using a Minimum Variance index and a closely related user-specified criterion. Under reasonable conditions, the performance of each output component in a MIMO system can be analysed independently. We define a sensitivity measure that relates system performance to model-plant mismatch, and use it to explore this sensitivity for three realistic types of parametric modelling errors. Next, we suggest a quantitative method that compares a system's actual output to its desired response in a transient setting. The performance of the transient response is demonstrably more sensitive to the model-plant mismatch than the steady state performance. The results are illustrated on industrial paper machine data.