Immersion and Invariance-based Sliding Mode Attitude Control of Tilt Tri-rotor UAV in Helicopter Mode
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ISSN:1598-6446 eISSN:2005-4092 http://www.springer.com/12555
Immersion and Invariance-based Sliding Mode Attitude Control of Tilt Tri-rotor UAV in Helicopter Mode Li Yu, Guang He*, Shulong Zhao, Xiangke Wang, and Lincheng Shen Abstract: In this paper, we propose an immersion and invariance-based sliding mode controller for a tilt tri-rotor unmanned aerial vehicle subjects to parameter perturbation, unmodeled dynamics, and external disturbances. The control scheme is divided into three parts, including the disturbance observer, the attitude controller, and the control allocation. Firstly, to alleviate the chattering and improve the robustness for attitude control, the observer using immersion and invariance theory is developed to estimate the disturbance. Note that the observer can relax the requirement of disturbance upper bound and guarantee the convergence of the estimation error. Secondly, to improve the dynamic response capability, a sliding mode attitude controller with an adaptive switch function is designed based on the disturbance observer. Thirdly, a hierarchical control allocation algorithm is proposed. The performance improvement is illustrated by comparing with other sliding mode controllers. Simulations and flight experiments are conducted to verify the effectiveness and applicability of the proposed control scheme. Keywords: Control allocation, disturbance observer, sliding mode control, tilt tri-rotor UAV.
1.
INTRODUCTION
Tilt-rotor unmanned aerial vehicle (UAV) is a novel aircraft with three flight modes, including the helicopter mode, the transition mode, and the fixed-wing mode. In the helicopter mode, it enjoys the vertical take-off and landing (VTOL) capability, so that it is not necessary for a runway, and it can be applied to many special situations such as aircraft carrier or surface warship. In the fixedwing mode, long-distance transportation can be achieved due to its long endurance and high cruise speed. The tiltrotor UAV that combines the advantages of the helicopter and the fixed-wing has received considerable attention in recent decades [1]. Most of the early studies are focused on dual tilt-rotor aircrafts such as XV-15 and V-22 [2]. Based on related technologies and similar configuration, the Eagle Eye and SmartUAV are developed [3–5]. However, the dual tiltrotor UAVs have not come into extensive use due to the complicated structure and aerodynamic interference between the rotors and wings. To overcome the difficulties, more rotors are applied for relaxing the requirement of the swashplate which is an indispensable part of helicopters. The tilt tri-rotor UAV, quad tilt-rotor UAV, and tilt-wing UAV are designed for simplifying the aircraft
structure and reducing the aerodynamic interference simultaneously. The quad tilt-rotor UAV has two pairs of tiltable rotors that are mounted on both sides of the fuselage [6–8], such that the aerodynamic interference can be reduced. For the tilt-wing UAV [9, 10], the rotors are assembled at the center of wings, and the rotors can tilt together
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