# Robust Path Following Control

#### Objective

Design a robust nonlinear path following control law for a fixed-wing UAV to track a reference path under the wind disturbance

#### Disturbance Observer

System model for the wind estimator

$$\begin{bmatrix} \dot{x} \\ \dot{y} \end{bmatrix} = \begin{bmatrix} V_a \cos \psi + W_N \\ V_a \sin \psi + W_E \end{bmatrix}$$

Update law of the disturbance observer

$$\dot{\hat{\bf{w}}} = -T_w \hat{\bf{w}} + T_w ( \dot{\bf{x}} – \bf{u})$$
where, $$\hat{\bf{w}} = \begin{bmatrix} \hat W_n & \hat W_e \end{bmatrix}^T$$ is the wind velocity estimate in the north and east direction, $$T_w$$ is the diagonal observer gain matrix, and $$\bf{u} = \begin{bmatrix} V_a \cos \psi & V_a \sin \psi \end{bmatrix}^T$$

#### System Model

The error kinematics model becomes,

\begin{align} \dot{e}_t &= V_g \cos (\chi – \chi_r ) – ( 1 – \kappa (s) e_n ) \dot{s} \\ \dot{e}_n &= V_g \sin (\chi – \chi_r ) – \kappa (s) e_t \dot{s} \end{align}

#### Path Following Control Law

Command Filtered Backstepping

## Hardware-in-the-loop Tests

Bspline Path Following

## Flight Tests

Circular trajectory following

#### Conclusion

The experimental results show that the improved tracking performance as well as the enhanced robustness, proving the applicability of the proposed algorithm in the various mission of the fixed-wing UAV in wind disturbance environment.

#### Researcher

김수현(Kim Su Hyeon)
한국항공대학교 스마트항공모빌리티학과 무인시스템제어연구실(KAU USCL)
박사과정
10540 경기도 고양시 덕양구 항공대학로 76 전자관 322호
angelfive92@gmail.com