Robust Nonlinear Dynamic Inversion Control for a Hypersonic Cruise Vehicle

Abstract

A Dynamic Inversion control law is designed for a conceptual hypersonic cruise vehicle. This control laws requires an onboard model that cancels the nonlinear dynamics of the vehicle so that the desired command responses of the closed-loop system can be achieved. For application to hypersonic cruise vehicles, the aerodynamic parameter uncertainties can become large and result in poor controller robustness properties. To explicitly quantify the stability and performance robustness properties, the Structured Singular Value (SSV), or μ-analysis, in combination with the DI controller is first formulated. The aerodynamic parameter uncertainties are represented via the linear fractional transformation (LFT) approach. The sensitivities of the closed-system stability margins with respect to simultaneous parameter variations are analyzed. Information gained from both forms of robust analysis is then used to determine the appropriate controller modifications to improve robustness to modeled aerodynamic uncertainties. The improved robustness properties are then demonstrated through μ-analysis.