Nonlinear Disturbance Observer Based Path Following for a Small Fixed Wing UAV

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Title
Nonlinear Disturbance Observer Based Path Following for a Small Fixed Wing UAV
Other Titles
소형 고정익 무인항공기의 비선형 외란 관측기 기반 경로 추종
Author
Shin, Dongmin
Advisor
Oh, Hyondong
Keywords
외란관측기, 무인기, 고정익
Issue Date
2019-08
Publisher
Graduate School of UNIST
Abstract
Small fixed-wing UAVs are increasingly attracting attention due to many applications in both military operations such as surveillance, and civilian domains such as powerline patrol and aerial photography. Their popularity growth has reduced the weight and size of small fixed-wing UAVs. They are vulnerable to external disturbances, such as wind due to their reduced size and weight. Disturbance has adverse effects on small fixed-wing UAVs, as it lowers the stability and performance of the control system during the operation. The disturbance includes modeling errors caused by the uncertainty of the system parameters as well as the wind from the external environment. The disturbance effects acting on small fixed-wing UAVs must be considered explicitly and eliminated eventually. In this regard, various control techniques for compensating the disturbance have been actively studied in control fields. Representative controller design techniques for compensating the disturbance include robust control (RC), sliding mode control (SMC) and adaptive control (AC), and disturbance observer-based control (DOBC). Most of the control techniques cause a slow response in attenuating disturbance effects since feedback control is performed based on tracking errors. Therefore, there is a need to compensate directly for disturbance through feedforward control. The disturbance observer-based control scheme directly estimates the uncertainty of the system, external disturbance, and directly compensates the estimated disturbance through the feedforward. This paper proposes a nonlinear disturbance observer-based path following controller for a small fixed-wing UAV affected by disturbance such as wind. We used a nonlinear disturbance observer-based control (NDOBC) method for precise path following for a small fixed-wing UAV along with the Lyapunov guidance vector field (LGVF) technique. The disturbance is estimated by a nonlinear disturbance observer, and then it is incorporated into the LGVF path following controller to compensate disturbance effects. The numerical simulation is first carried out through the MATLAB Simulink environment. Software in the loop simulation (SITL) is carried out to verify its performance. Outdoor flight experiments are performed to demonstrate its performance in a real-world environment.
Description
Department of Mechanical Engineering
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