Nonlinearity assessment of chemical processes

One of the most important issues in controller design and analysis of a nonlinear system is its degree of nonlinearity. Helbig et al. proposed a method in which the system, along with a linear reference model (which is the sum of a couple of rst order transfer functions), is stimulated with a set of input patterns. The outputs of these systems are then compared and the nonlinearity measure of the system is obtained as the normalized dierence between the outputs of these two systems. In this paper, the linear reference model is replaced with two simpler linear ones. The proposed method has been used for assessment of the nonlinearity measure of various nonlinear systems that are used as standard benchmarks by the nonlinear process control research community. The results show that, despite the use of this simpler model with less parameters, the calculated nonlinearity measure is almost similar to the one obtained by Helbigʹs method. Furthermore, the nonlinearity measure obtained by the proposed method can be calculated very much faster.