An integrated fault diagnosis and safe-parking framework for fault-tolerant control of nonlinear systems

In this work, we consider the problem of designing an integrated fault diagnosis and fault-handling framework to deal with actuator faults in nonlinear systems. A model-based fault diagnosis design is first proposed, which can not only identify the failed actuator but also estimate the fault magnitude. The fault information is obtained by estimating the outputs of the actuators and comparing them with the corresponding prescribed control inputs. This methodology is developed under state feedback control and generalized to deal with state estimation errors. Then the safe-parking framework developed previously (to handle the case where the failed actuator reverts to a known fixed value) for fault-tolerant control is extended to handle the case where an actuator seizes at an arbitrary value. The estimate of the failed actuator position provided by the fault diagnosis design is used to choose a safe-park point, at which the system operates temporarily during fault repair, from those generated offline for a series of design values of the failed actuator position. The discrepancy between the actual value of the failed actuator position and the corresponding design value is handled through the robustness of the control design. The efficacy of the integrated fault diagnosis and safe-parking framework is demonstrated through a chemical reactor example. Copyright (C) 2011 John Wiley & Sons, Ltd.