The optimal control structure: an approach to measuring control-law nonlinearity

This paper introduces the Optimal Control Structure as a design tool to examine the control-law nonlinearity of a given process design. Control-law nonlinearity is defined as the optimal degree of nonlinear compensation in the controller, a system property distinct from open-loop nonlinearity. It is determined by the nature of the open-loop process, the performance objective, and the region of operation. The Optimal Control Structure contains the structural dynamics of the optimal control law, and an assessment of the control-law nonlinearity can be found from any open-loop nonlinearity measure of this structure that takes into account a region of operation. This approach is applied to three SISO models, demonstrating how the control-law nonlinearity for a given plant can vary with the cost of control action and performance objective.

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