Saturation nonlinearities are ubiquitous in engineering systems. In
control systems, every physical actuator or sensor is subject to
saturation owing to its maximum and minimum limits. A digital filter is
subject to saturation if it is implemented in a finite word length
format. Saturation nonlinearities are also purposely introduced into
engineering systems such as control sys- tems and neural network
systems. Regardless of how saturation arises, the analysis and design of
a system that contains saturation nonlinearities is an important
problem. Not only is this problem theoretically challenging, but it is
also practically imperative. This book intends to study control systems
with actuator saturation in a systematic way. It will also present some
related results on systems with state saturation or sensor saturation.
Roughly speaking, there are two strategies for dealing with actuator
sat- uration. The first strategy is to neglect the saturation in the
first stage of the control design process, and then to add some
problem-specific schemes to deal with the adverse effects caused by
saturation. These schemes, known as anti-windup schemes, are typically
introduced using ad hoc modifications and extensive simulations. The
basic idea behind these schemes is to intro- duce additional feedbacks
in such a way that the actuator stays properly within its limits. Most
of these schemes lead to improved performance but poorly understood
stability properties.
