Uncertainty modeling and fixed-order controller design for a hypersonic vehicle model

Control system design for hypersonic vehicles will be complicated by coupling effects between aerodynamics, propulsion, and structure. Using H-infinity and mu-synthesis techniques, these features can be modeled as uncertainties and incorporated into the design procedure of a flight control system. However, modern control theory techniques generally lead to high-order controllers, The time delays, which are created when these controllers are implemented, may not be acceptable. A technique to constrain controller dimension a priori in the design process is used to design fixed-order mu controllers that are robust to mixed real/complex uncertainties. Typical hypersonic effects such as propulsion system perturbations and aeroelastic fuselage bending are modeled as uncertainties in a robust control design framework. Three different fixed-order controllers are synthesized for a hypersonic vehicle model accelerating through Mach 8. A comparison with full-order and reduced-order designs is conducted and the results illustrate that the fixed-order controllers exhibit robustness properties similar to full order designs while considerably reducing controller complexity.