Integrated Robust Identification and Control of Large-Scale Processes

We propose the use of pseudo-singular values, which are closely related to singular values but are allowed to have sign, as a convenient approach for developing techniques for the identification and control of large-scale processes. Steady-state controllability can be assessed directly in terms of the pseudo-singular values. It is shown that to control an output disturbance direction with zero steady-state error it is necessary to correctly identify the sign of the corresponding pseudosingular value. At the identification stage, this motivates the estimation of confidence intervals for the pseudo-singular values from input-output data. A controller with integral action should not attempt to manipulate in process input directions corresponding to output disturbance directions that cannot be controlled with confidence. These principles motivate a controller structure appropriate for providing the robust control of poorly conditioned large-scale processes. Any controller design technique can be applied to produce a controller with the proposed controller structure. The controllability results and the integrated identification/controller design procedure are illustrated using an industrial paper machine example.