Abstract-Constrained Nonlinear Model Predictive Control (NMPC) is shown to have potentials for reconfigurable fault tolerant control of highly nonlinear, intrinsically unstable, high performance aircraft. Results on fault tolerance of NMPC autopilots were obtained for an F-16 fighter aircraft model, without the implementation of any prestabilizing controllers. It has been shown that NMPC has inherent fault detection capabilities due to its effective utilization of feedback and its internal model predictions. Actuator (control surface) faults, including extreme cases of total actuator failure are examined as test cases for the NMPC reconfigurable fault tolerant control scheme developed in this work. The NMPC autopilots implementation and simulations were done using the ACADO nonlinear optimization solver.
I. INTRODUCTIONThe increasing complexity of modern and future flight control systems demands advanced and reliable control techniques that will ensure safety and survivability. When faults occur, it is very important that system stability is maintained and an acceptable system performance is attained.The reconfigurable fault-tolerant control systems review in [1] highlights important limitations on conventional approaches to solving reconfigurable control problems for constrained multivariable systems and systems with significant nonlinearities. In general, how to design fault-tolerant control systems which can work effectively in the entire range of nonlinear systems, and how to distinguish the changes induced by faults from that by operating condition variations is still a challenge.In the past few decades it became apparent that predictive control methods display qualities that could be utilized in complex, nonlinear flight control applications [2]. Model predictive control, in general, has been identified as a method that offers good possibilities for reconfiguration and fault-tolerant control [1], [3]-[6]. This claim is simply due to model predictive control's ability of handling most of the challenges of reconfigurable control in a generic and systematic manner. The choice of NMPC over standard nonlinear control methods is therefore justified by the fact that they are not developed in order to handle constraints in a systematic way. In addition, many nonlinear methods depend on complicated design procedures that do not scale well to large systems [7].Most fault tolerant control systems rely on or integrate fault detection and diagnosis (FDD) subsystems in order to