Robust flight control based on a nonlinear-L1 adaptive control with modified piecewise-constant and HIL experiments

This paper presents a novel nonlinear dynamic inversion-based L1 adaptive control (NDI-L1) for fixed-wing aircraft with strong nonlinearity, model uncertainties, and center of gravity variations. This adaptive structure can decouple the system's fast adaptation and robustness, thus reducing the oscillations caused by high adaptation gain. Moreover, compared to existing L1 adaptive control, NDI-L1 control enlarges its application range, providing satisfactory dynamic performance as well as robustness within the flight envelope. Additionally, this paper also improves the existing piecewise-constant adaptation (PCA), addressing the contradiction between estimation accuracy and sampling time. The modified PCA achieves the desired estimation accuracy while effectively reducing the computational burden. The dynamic performance of the proposed adaptive structure under disturbance is theoretically analyzed. Importantly, the robust flight controller is designed based on the proposed NDI-L1 to eliminate the influences of parameter perturbations and sudden changes in the center of gravity on flight dynamics. Simulations and hardware-in-the-loop experimental results clearly confirm the effectiveness, advantages, and robustness of the proposed NDI-L1 with modified PCA, and compare it to other existing methods.