H∞ robustification of a paper machine cross-directional control system

This paper considers H-infinity robustification of an industrial paper machine cross-directional (CD) control system. The existing industrial controller is reinterpreted as a precompensator weight for shaping the open-loop response. The robustification is then achieved by performing a robust stabilization of the nominal plant model and industrial controlled Hinfinity combination. The large scale (226 inputs and 226 outputs) optimization problem is decoupled into 226 independent SISO systems by an application of recent results for spatially invariant systems. The robustified closed-loop is then implemented by augmenting the industrial controller with a low-order prefilter. It is then demonstrated that the robustness of the closed-loop system has been significantly improved while its performance remains well-preserved.