Fault_Tolerant Control of Nonlinear Processes_Performance-Based

Fault_Tolerant Control of Nonlinear Processes_Performance-Based

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Fault-Tolerant Control of Nonlinear Processes: Performance-Based Recon±guration and Robustness * Prashant Mhaskar , Adiwinata Gani and Panagiotis D. Christofdes Department oF Chemical and Biomolecular Engineering University oF CaliFornia, Los Angeles, CA 90095 Abstract — This work considers the problem of control system/actuator failures in nonlinear processes subject to input constraints and presents two approaches for fault- tolerant control that focus on incorporating performance and robustness considerations, respectively. In both approaches, ±rst a family of candidate control con±gurations, characterized by different manipulated inputs, is identi±ed for the process under consideration. Performance considerations are ±rst incorporated via the design of a Lyapunov-based predictive controller that enforces closed-loop stability from an explicitly characterized set of initial conditions (computed using an auxiliary Lyapunov-based 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 con±guration) to ascertain the suitability of a candidate backup con±guration and then performance considerations are again considered in choosing between the suitable backup con±gurations. Next, we consider the problem of implementing fault-tolerant control to nonlinear processes subject to input constraints and uncertainty. To this end, we ±rst design a robust hybrid predictive controller for each candidate control con±guration 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 con±gurations. Key words : ±ault-tolerant control, Nonlinear systems, Input constraints, Model predictive control, Closed–loop stability region, Process control. I. INTRODUCTION The operation oF modern-day chemical plants involves an interconnection oF complex processing units via mate- rial and energy ²ows through recycle streams. Aided by the advances in sensing, communicating and computing technologies, chemical plant operation is relying exten- sively on automated process control systems to satisFy simultaneously the (sometimes con²icting) requirements oF saFety, reliability and proftability. Increased automation, however, also makes the plant susceptible to Faults (e.g., deFects/malFunctions in process equipment, sensors and actuators, Failures in the controllers or in the control loops) that can result in substantial fnancial losses and/or saFety hazards iF not addressed within a time appropriate to the context oF the process dynamics.
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This note was uploaded on 08/19/2011 for the course ELECTRICAL 134 taught by Professor Haeri during the Spring '11 term at Amirkabir University of Technology.

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Fault_Tolerant Control of Nonlinear Processes_Performance-Based

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