Coupling-observer-based nonlinear control for flexible air-breathing hypersonic vehicles

This paper investigates the nonlinear control problem for flexible air-breathing hypersonic vehicles (FAHVs). The coupling dynamics between flexible and rigid-body parts of FAHVs may cause degradation of control performance or high-frequency oscillations of control input and flexible state. In this paper, the flexible effects produced by the coupling are modeled as a kind of unknown disturbance and included in the new control-design model, for which a coupling observer is constructed to estimate these effects. Thus, a novel nonlinear composite control strategy, which combines a coupling-observer-based feedforward compensator and a dynamic-inversion-based feedback controller, is proposed to reject the flexible effects on pitch rate and track desired trajectories of velocity and flight-path angle. The stability of composite closed-loop system is analyzed by using the Lyapunov theory. Simulation results on a full nonlinear model of FAHVs demonstrate that the presented controller is more effective by comparison with the previous scheme.