NONMINIMUM-PHASE COMPENSATION FOR NONLINEAR PROCESSES
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The design of controllers for nonlinear, nonminimumphase processes is one of the most difficult control problems currently faced. Current available control algorithms for nonlinear processes rely implicitly or explicitly on an inverse of the process. Linear control methods for nonminimumphase processes are based on a decomposition of the process into a minimumphase and a nonminimumphase part. Such a decomposition is an open problem for nonlinear systems. In this work, a control structure called the minimumphase output predictor for nonlinear, nonminimumphase processes is developed. The structure is based on the notion of statically equivalent outputs; a minimumphase, statically equivalent output is estimated online and then an available nonlinear control algorithm is used to control it to set point. The advantage of the proposed formulation is that it is based on the calculation of an output function, not on a decomposition of the process dynamics. The proposed control methodology is applied and its performance is evaluated for a chemical engineering example. Copyright 1992 American Institute of Chemical Engineers