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 pseudo-singular 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