Nonlinear Incremental Control for Flexible Aircraft Trajectory Tracking and Load Alleviation

TL;DR

This paper introduces a nonlinear control system for flexible aircraft that enhances trajectory tracking and reduces gust loads by using cascaded control loops and advanced sliding mode techniques.

Contribution

It presents a novel control architecture combining nonlinear dynamic inversion, incremental sliding mode, and backstepping sliding mode controls for flexible aircraft.

Findings

Effective trajectory tracking demonstrated in turbulence simulations.

Significant load alleviation achieved without compromising control performance.

Control method reduces dependency on precise model knowledge.

Abstract

This paper proposes a nonlinear control architecture for flexible aircraft simultaneous trajectory tracking and load alleviation. By exploiting the control redundancy, the gust and maneuver loads are alleviated without degrading the rigid-body command tracking performance. The proposed control architecture contains four cascaded control loops: position control, flight path control, attitude control, and optimal multi-objective wing control. Since the position kinematics are not influenced by model uncertainties, the nonlinear dynamic inversion control is applied. On the contrary, the flight path dynamics are perturbed by both model uncertainties and atmospheric disturbances; thus the incremental sliding mode control is adopted. Lyapunov-based analyses show that this method can simultaneously reduce the model dependency and the minimum possible gains of conventional sliding mode control methods. Moreover, the attitude dynamics are in the strict-feedback form; thus the incremental backstepping sliding mode control is applied. Furthermore, a novel load reference generator is designed to distinguish the necessary loads for performing maneuvers from the excessive loads. The load references are realized by the inner-loop optimal wing controller, while the excessive loads are naturalized by flaps without influencing the outer-loop tracking performance. The merits of the proposed control architecture are verified by trajectory tracking tasks and gust load alleviation tasks in spatial von Karman turbulence fields.