Good or Bad – When Is Plant Nonlinearity an Obstacle for Control?

Virtually every real process is a nonlinear system. Nevertheless, linear system analysis and linear controller design methods have proven to be adequate in many applications. On the other hand, there are nonlinear processes that require or benefit from nonlinear control. Therefore, recognizing a system as being nonlinear does not suffice, but the extent and severity of a system’s inherent nonlinearity is the crucial characteristic in order to decide whether linear system analysis and controller synthesis methods are adequate. The introduction of nonlinearity measures is an attempt to systematically approach this problem. In this contribution, we review existing approaches to nonlinearity assessment, we state the most important results and we give a glance ahead to what might be expected from this field in the future. Copyright © 2006 IFAC