This paper proposes a nonlinear (NL) fault-tolerant control (FTC) strategy for stabilizing the attitude of a quadrotor affected by multiple rotor failures. The recovery process relies mainly on progressive accommodation (PA) strategy. The latter uses the Newton-Raphson (NR) algorithm in order to solve the state-dependent Riccati Equation (SDRE) in a recursive way. Simulations are performed using the NL model of the quadrotor in fault-free and post-fault cases. Both PA and the direct SDRE methods are employed so that the attitude control of the quadrotor can be stabilized. The results show that the PA strategy performs better than the classical method when it comes to convergence speed and to preserving the control objectives of the nominal system.
The occurrence of failures in the control surfaces of an aircraft may become a serious threat to the safety of both aircraft and passengers. That is, using fault-tolerant control (FTC) is vital for such critical systems. The nonlinear progressive accommodation (NPA) is a FTC strategy that consists in solving the State-dependant Riccati Equation (SDRE) in an iterative way. The aim of this work is to study the efficiency of the NPA, in the case of a non-classical stabilization problem and a different modelling of a nonlinear (NL) system, affected by a total actuator failure. That is, a modified NPA strategy is proposed by combining the SDRE control and a feed-forward compensator, derived from the Forward-Propagation-Riccati-Equation (FPRE). The system considered in this paper is a full NL model of a DC-8 aircraft with coupled dynamics. The modelling of the aircraft as well as the simulation of the healthy, affected and accommodated system are presented. The proposed NPA method allows the aircraft to achieve a trajectory-following mission despite the complete failure of its actuator. Most importantly, by preserving the system's stability, the developed approach can be considered as a good alternative to the use of redundant actuators in aircraft.
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