Abstract:

Aircraft nonlinear dynamic systems usually include unmatched uncertainties consisting of unknown external disturbances and unmodelled dynamic terms. The affine nonlinear model of aircraft longitudinal motion is constructed. An adaptive backstepping nonsingular terminal sliding mode (AB-NTSM) control scheme is proposed for trajectory tracking, which is based on the nonlinear disturbance observer (NDO). Without the prior information of upper bounds of external disturbances, NDOs and adaptive laws are designed for external disturbances and unmodelled dynamic terms respectively, which can strengthen system robustness for uncertainties. Simulations of three kinds of cases are given, which demonstrate that NDOs can realize accurate observation of different kinds of external disturbances. Big observation errors only exist when the disturbance is discontinuous. Under the effects of system uncertainties, the proposed ABNTSM control scheme can realize stable tracking of desired trajectory, and the chattering of the system input can be effectively suppressed.