Computers & Chemical Engineering, Vol.21, No.9, 1009-1019, 1997
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.