Robust Stability and Performance Analysis of Incremental Dynamic Inversion-based Flight Control Laws

Incremental Nonlinear Dynamic Inversion (INDI) is a sensor-based control law design strategy that is based on the principles of feedback linearization. Contrary to its non-incremental counterpart (NDI), this design method does not rely on the availability of a high-fidelity on-board model of the airframe dynamics and is robust to aerodynamic variations. Consequently, INDI brings a natural and robust design approach to desirable flying qualities. However, robustness to singular perturbations, which may arise due to transportation lags, elastic airframe effects, or other types of badly modelled or unknown dynamics, is a known challenge for INDI-based control laws. In this article, the general stability and performance robustness properties of INDI and its linear form (IDI) are described analytically and analyzed in a flight control law design study by means of the structured singular value frame framework. In addition, inversion loop augmentation solutions are investigated using automated synthesis to further improve the robustness characteristics of basic IDI designs.