Control of Linear Plants with Actuators Subject to Hard Constraints

Washington State University, Pullman WA

Investigators

Abstract

As well known, practical control problems are always dominated by constraints. Until recently these constraints have been conspicuously absent from almost all-modern control literature, as taking such constraints into account leads to hard complex nonlinear problems. On the other hand, ignoring such constraints can be detrimental to the stability and performance of control systems. There are disastrous examples for detrimental effect of neglecting constraints such as the Chernobyl unit 4 nuclear power plant disaster in 1986 or YF-22 crash of April 19. One of the most commonly encountered constraints in control engineering is the actuator's constraint and limitations. Actuator magnitude and rate saturations are some of the most common and significant constraints in a control system. Taking such constraints in analysis and design of control systems immensely increases the industrial relevance of modern control theory. During the 90's we have witnessed renewed and intense research activity in the area of control of linear plants with constrained actuators. This research area is broadly viewed as one of the major areas of research in nonlinear control theory. In the past few years, the research activities in this area including the work of this investigator and his co-workers have given rise to the emergence of powerful analysis and design tools for control systems with actuator constraints. Using the structure of amplitude and rate saturation nonlinearity in a meaningful way, this investigator and his co-workers through the support of a prior NSF grant produced a body of work that concerns with (a) external stability, (b) internal stability, (c) external as well as internal stability, (d) output regulation, and (e) additive disturbance rejection in both global and semiglobal framework. The performance and robustness issues whenever actuators are subject to amplitude and rate constraints are not dealt with in the literature or in our prior work. Hence, dealing with performance and robustness issues is a natural next step for research in this area, and is the focus of this proposal. The problems associated with performance and robustness issues whenever actuators are constrained, though complex and challenging, are highly crucial for control engineering applications and thus should be viewed as fundamental research problems in nonlinear control theory. This proposal formulates a number of research tasks, which form the core of this nonlinear research area.