Gain-Scheduled H-Infinity Control and Analysis of a Nonlinear Generic Hypersonic Vehicle.

摘要

The concept of hypersonic flight has been around for many years. In recent years, emerging technologies and market forces have renewed latent interest in this challenging field. With many private and government institutions driving new innovations, these concepts are becoming reality. New research is needed to facilitate future innovation and deployment. The complex dynamic behaviors within the hypersonic flight envelope must be studied for designers to either mitigate or compensate for their effects on future vehicles. Control techniques must be adapted to suit the unstable and highly nonlinear dynamics of such systems. This work has two goals: to explore the dynamic characteristics of hypersonic flight and to control such a vehicle in the face of non-linearly changing dynamics. A nonlinear, 6 degree of freedom dynamic model of a Generic Hypersonic Vehicle is developed. The model integrates changing mass, moments of inertia, and center of gravity as a function of fuel burn. A bank of spline interpolation tables generates aerodynamic coefficients dependent on speed, angle of attack, and control surface deflections for the entire flight envelope. The nonlinear model of the full flight envelope is then reduced to a series of linear models to represent the aircraft trimmed under straight and level flight conditions over the range of Mach numbers, Mach 2 to 23. The changing Longitudinal and Lateral dynamics of the linearized system are analyzed as a function of Mach number using standard linear techniques to show the changing vehicle characteristics. A spline-based gain-scheduled, H-infinity controller is also designed for a subset of the linear systems. The controller stabilizes the system between Mach 4.9 and 7.1, with aircraft weight ranging from 160,000 to 230,000 pounds and from 68,000 to 92,000 feet altitude. The controller maintains system stability while commanded to change both Mach number and altitude within the gain-scheduled envelope. Additionally, the controller's performance is assessed in the presence of low frequency disturbances.