Abstract
This paper presents nonlinear, singularity-free autopilot designs for multivariable reduced-attitude control of fixed-wing aircraft. To control roll and pitch angles, we employ vector coordinates constrained to the unit two-sphere and that are independent of the yaw/heading angle. The angular velocity projected onto this vector is enforced to satisfy the coordinated-turn equation. We exploit model structure in the design and prove almost global asymptotic stability using Lyapunov-based tools. Slowly-varying aerodynamic disturbances are compensated for using adaptive backstepping. To emphasize the practical application of our result, we also establish the ultimate boundedness of the solutions under a simplified controller that only depends on rough estimates of the control-effectiveness matrix. The controller design can be used with state-of-the-art guidance systems for fixed-wing unmanned aerial vehicles (UAVs) and is implemented in the open-source autopilot ArduPilot for validation through realistic software-in-the-loop (SITL) simulations.
Highlights
Technology advancements have led to increased use of small unmanned aerial vehicles (UAVs) in civil, commercial, and scientific applications
Fixed-wing UAVs [1], as illustrated in Figure 1, have superior range and endurance when compared to rotary-wing UAVs, which enable applications such as environmental monitoring, search and rescue, aerial surveillance and mapping, and medical transportation [2]
Fixed-wing UAVs have to resort to using guidance schemes [4], where the UAV’s geometric path in 3-D space is controlled by specifying course and flight path angle commands to lower-level autopilots [5]
Summary
Technology advancements have led to increased use of small unmanned aerial vehicles (UAVs) in civil, commercial, and scientific applications. This has led to a significant research effort into socalled geometric attitude control, where singularity-free controllers are designed directly on SO(3), using rotation matrices, that avoid the unwinding phenomenon and often controls the system along geodesics, i.e., paths of minimum length in rotation space [28,29,30,31,32,33] These advantages are desirable when the controlled vehicle is subject to large angle rotations, e.g., a fixed-wing UAV recovering from large attitude errors resulting from severe wind gusts [34]. Global asymptotic stability can be achieved by using tools from hybrid dynamical systems, where hysteresis-based switching ensures that all trajectories converge to the desired equilibrium [49,50,52,54,55,56,57]
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