Abstract
This work considers the problem of control system/actuator failures in nonlinear processes subject to input constraints and presents two approaches for faultโtolerant control that focus on incorporating performance and robustness considerations, respectively. In both approaches, first a family of candidate control configurations, characterized by different manipulated inputs, is identified for the process under consideration. Performance considerations are first incorporated via the design of a Lyapunovโbased predictive controller that enforces closedโloop stability from an explicitly characterized set of initial conditions (computed using an auxiliary Lyapunovโbased nonlinear controller). A hierarchical switching policy is derived, that uses stability considerations (evaluated via the presence of the state in the stability region of a control configuration) to ascertain the suitability of a candidate backup configuration and then performance considerations are again considered in choosing between the suitable backup configurations. Next, we consider the problem of implementing faultโtolerant control to nonlinear processes subject to input constraints and uncertainty. To this end, we first design a robust hybrid predictive controller for each candidate control configuration that guarantees stability from an explicitly characterized set of initial conditions, subject to uncertainty and constraints. A switching policy is then derived to orchestrate the activation/deactivation of the constituent control configurations. Finally, simulation studies are presented to demonstrate the implementation and evaluate the effectiveness of the proposed faultโtolerant control method. Copyright ยฉ 2005 John Wiley & Sons, Ltd.