Robust Tracking of the Flight Path Angle of Aircraft Based on UDE and IID.pdf

Robust Tracking of the Flight Path Angle of Aircraft Based on UDE and IID Fei Wu, Qiang Liu, Bo Zhu Institute of Astronautics and Aeronautics, University of Electronic Science and Technology of China, Chengdu, China wf_mail@163.com, chubo@ Abstract—Nonlinear robust tracking of the flight-path angle in the longitudinal channel of aircraft is a challenging control problem. The main difficulty results from its non-minimum phase characteristics and the unavoidable uncertainty and disturbances existing in the internal dynamics. To solve the problem, this paper presents a nonlinear control scheme based on an Uncertainty and Disturbance Estimator (UDE) and the causal Ideal Internal Dynamics (IID), taking an F-16 aircraft model as the illustrative example. A significant feature of the presented scheme is that it does not need any information about the uncertainties, and that it can be implemented in real time due to the causality of the inversion of the internal dynamics. A numerical simulation example is given to show the effectiveness of the scheme. Keywords: Non-minimum phase, output tracking, robustness, UDE, causality, IID I. INTRODUCTION A nonlinear control system is of non-minimum phase if its zero dynamics are unstable [1]. Many practical control plants, such as aircraft and inverted pendulums, are non- minimum phase. Hence, tracking of non-minimum phase output is a real-life control problem. In flight control engineering, the non-minimum phase characteristic of aircraft is usually neglected for simplicity and various PID (Proportional-Integral-Differential) controllers are applied. Though the PID control scheme is effective in common cases, it cannot achieve a perfect tracking and the robustness with respect to non-constant external disturbances is another problem [2]. Therefore, it is necessary to develop other robust control methods, taking the non-minimum phase characteristic of the aircraft plant into account. Actually, n