Immersion and invariance control for Euler angles of a fixed‐wing unmanned aerial vehicle

Abstract

In this paper, an asymptotically stabilizing, nonlinear flight controller design via immersion and invariance (I&I) approach for a fixed-wing unmanned aerial vehicle is presented. The objective is to adjust pitch, roll, and yaw angles with the control inputs aileron, elevator, and rudder deflections. The important issues in designing a controller for fixed-wing unmanned aerial vehicles (UAVs) are to cope with its nonlinear dynamics and to obtain a controller that can deal with various disturbances. Existing linear controllers cannot deal well with the nonlinear dynamics of the UAVs and that can not guarantee stability outside of the considered operating point. On the other hand, widely used nonlinear controllers have some weaknesses. Such as sliding mode controllers are robust to disturbances but suffer from the chattering phenomenon, and the backstepping controllers are not very robust to disturbances. The proposed controller ensures global stability with smooth and precise reference tracking and also yields significant disturbance attenuation without the chattering phenomenon.I&I approach also enables us to directly assign closed-loop dynamics. Thus, tuning of the proposed controller is straightforward. Most of the other nonlinear methods do not have straightforward tuning of control parameters to assign desired dynamics to a closed-loop system. The superior performance of the proposed controller is shown via simulations for various disturbances in comparison with the sliding mode controllers; the one with standard control law and the one with modified control law that eliminate the chattering phenomenon. KEYWORDS immersion and invariance, nonlinear flight control, stabilizing control, unmanned aerial vehicle INTRODUCTIONUnmanned aerial vehicles (UAV) have applications in many different areas. Detection of natural disasters, monitoring of power lines and pipelines, search and rescue, prevention of crime, and military applications are the most needed areas for UAVs. Their importance increases especially in situations where the danger is high and human access or skills are limited. Fixed-wing UAVs have several advantages over rotary-wing UAVs. Because of their conventional design, they have more flight duration, payload capacity, longer range, and higher speed. Therefore, they are more feasible for the given tasks.Different techniques are developed to control fixed-wing UAVs in the literature. Traditionally, linearized models of aircraft dynamics are used in several studies based on