1 An Intelligent Hierarchical Approach to Actuator Fault Diagnosis and Accommodation Xiaodong Zhang*, Yong Liu*, Rolf Rysdyk + , Chiman Kwan*, Roger Xu* *Intelligent Automation Inc., 15400 Calhoun Drive, Suite 400, Rockville, MD 20855 Telephone: (301)-294-5238, Email:ckwan@i-a-i.com + Department of Aeronautics & Astronautics, University of Washington, Seattle, WA 98105-2400, USA Telephone: (206) 543-6725, Email: rysdyk@aa.washington.edu Abstract—This paper 1,2 presents a novel intelligent hierarchical approach to automatically detecting, isolating, and accommodating faults in flight control systems. The proposed architecture has three main components. First, a new nonlinear fault diagnosis scheme is used to detect the occurrence of any faults and to determine the particular component that has failed. Second, a controller module consists of a primary nominal controller and a secondary adaptive fault-tolerant controller. While the nominal controller can be any existing conventional flight control system, the secondary neural network (NN) based nonlinear adaptive controller is designed to maintain acceptable control performance after the detection of fault occurrence. Third, a reconfiguration supervisor makes decision regarding controller reconfiguration and control reallocation by using on-line diagnostic information. Following failures of primary aerodynamic actuators, flight safety can be maintained by utilizing alternative actuation systems for critical stability and control augmentation tasks. The effectiveness of the proposed integrated fault diagnosis and accommodation approach has been illustrated by using the Research Civil Aircraft Model (RCAM) developed by the Group for Aeronautical Research and technology in Europe (GARTEUR). Extensive simulation studies have clearly shown the benefits of the proposed adaptive fault- tolerant control scheme using on-line diagnostic information. TABLE OF CONTENTS 1. INTRODUCTION...................................................... 1 2. FAULT-TOLERANT CONTROL ARCHITECTURE ..... 2 3. FAULT DETECTION AND ISOLATION SCHEME ...... 4 4. NONLINEAR ADAPTIVE FLIGHT CONTROL .......... 4 5. SIMULATION RESULT ............................................ 6 ACKNOWLEDGEMENT ............................................... 8 REFERENCES ............................................................. 8 1 1 0-7803-9546-8/06/$20.00© 2006 IEEE 2 IEEEAC paper #1537 BIOGRAPHY ............................................................ 15 1. INTRODUCTION Aerodynamic actuator failures have become a significant concern for flight safety. Recent accidents have been caused by a single actuator failure or a complete loss of the whole hydraulic actuation system [9]. A fault-tolerant control (FTC) system is capable both of automatically compensating for the effects of faults and of maintaining the performance of the control system, at some acceptable level, even in the presence of faults. A traditional approach to fault-tolerance is to use robust control design for anticipated faults, which is, in general, a conservative approach and may sacrifice achivable performance under normal operating conditions. In contrast, an active fault-tolerant control system that automatically detects and identifies component failures and adapts to such failures as they occur has the potential to achieve superior performance throughtout the full flight operations. Moreover, a truly fault-tolerant control system must also be able to accommodate new and unanticipated faults. In addition, the desire for enhanced agility and functionality demands that future aircraft perform over an increased range of operating conditions characterized by dramatic variations in dynamic pressure and nonlinear aerodynamic phenomena. Consequently, the dynamics of vehicles are usually highly nonlinear and poorly modeled or rapidly changing. Traditional model-based fault diagnosis and flight control designs involve linearizing the vehicle dynamics about several operating conditions and blending the linear health monitors and controllers for these operating points through gain scheduling, which tends to be rather tedious. Moreover, when the effect of various faults has to be taken into account, the size and complexity of the scheduling table is significantly increased, which makes it very difficult for design and real-time implementation. Therefore, future designs will benefit from more advanced methods, which are directly based on intrinsic nonlinearities of the vehicle while avoiding prohibitively complex gain scheduling.