Fast inner-loop control of air-breathing hypersonic vehicles

This paper investigates the inner-loop attitude and velocity control problem for air-breathing hypersonic vehicles subject to practically constrained actuators. Traditional nonlinear dynamic inverse (NDI) is enhanced by an intelligent control allocation (ICA) to realise the low-complexity attitude decoupling. The ICA addresses various characteristics of aerodynamic control surfaces while providing an efficient detecting mechanism for allocation errors. Within the ICA-NDI frame, a finite-time disturbance observer-based terminal sliding mode (FTDO-based TSM) attitude controller regulates Euler angles in the fast manner. This attitude controller employs an improved integral sliding surface containing necessary information from both ICA detection and FTDO estimation, which, therefore, is capable of accommodating constrained control surfaces and rejecting mismatched disturbances. Meanwhile, an adaptive governor adjusts the velocity reference according to the current saturation level of the scramjet fuel-to-air equivalency ratio. The governor is further integrated to a baseline adaptive velocity controller to synthetically handle scramjet input saturations and uncertain factors.