Controller Design for Nonlinear Multi-Input/Multi-Output Systems Using the Contoured Robust Controller Bode Plot

In this paper, a novel approach to controller design for non-linear multi–input/multi–output (MIMO) systems is presented based on the Contoured Robust Controller Bode (CRCBode) plot. CRCBode plots show level–sets of a robust metric and identify certain “forbidden regions” on the controller Bode magnitude and phase plots such that intersections of the controller frequency response with these forbidden regions indicate that a robust stability and performance criterion is violated. Nonlinear system dynamics are included as a structured uncertainty set consisting of linearizations about several operating points. To demonstrate this approach, we design a controller for a MIMO high–speed, low–tension magnetic tape drive memory system. A preliminary approximate inverse step is described, followed by several loop–shaping design iterations to eliminate all intersections with the forbidden regions on the CRCBode diagrams. Finally, the CRCBode compensator is compared to one generated using an automated H_∞ synthesis algorithm.