Actuator Fault Diagnosis and Accommodation for Improved Flight Safety

This paper presents an adaptive fault diagnosis and accommodation scheme for aerodynamic actuators. The fault-tolerant control architecture consists of three main components: an online nonlinear fault detection and isolation scheme, a controller suite, and a reconfiguration supervisor which performs controller reconfiguration and control reallocation using online diagnostic information. The proposed scheme provides a unified architecture for fault detection, isolation and accommodation of actuator failures. Simulation studies using a nonlinear 'Beaver' aircraft model have shown the effectiveness of the proposed scheme. 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 fault-tolerant flight control system will benefit from more advanced methods, which are directly based on intrinsic nonlinear dynamics of the vehicle. The design and analysis of fault diagnosis algorithms based on the model-based analytical redundancy approach have received significant attention during the last two decades (3), (4), (5). Recently there has also been a lot of research activity on fault diagnosis and accommodation of nonlinear systems (5), (6), (7), (8), (9), (10). The fault information generated by the detection and isolation procedures can be very useful to fault-tolerant control design. In this paper, we present a unified nonlinear framework for detection, isolation, and accommodation of aerodynamic actuator faults. It is an application of the fault diagnosis and accommodation architecture presented in previous papers (9), (10). The proposed architecture consists of three components: a fault diagnosis scheme, a controller suite, and a reconfiguration supervisor. The first part of this research work, i.e.., detailed design and analysis of the controller suite, has been described in our previous paper (11) and will only be briefly summarized here. A nonlinear DHC-2 'Beaver' aircraft (12) is used to illustrate the effectiveness of overall fault-tolerant control design.