Fast Time-Varying Uncertainty Resisting for Hybrid UAV by Hierarchical Yaw Control with Constrained Input

Yaw control for aircraft using the rudder faces challenges in resisting fast time-varying uncertainty due to the relatively slower response of the rudder. In hybrid unmanned aerial vehicles equipped with both rudders and rotors, the introduction of powered yaw control offers novel solutions for addressing fast time-varying uncertainty by leveraging the quicker response of rotors compared to traditional rudders. This paper presents a hierarchical yaw control approach for hybrid unmanned aerial vehicles, comprising a nominal control for rudders to achieve the desired yaw tracking and a constrained powered yaw control for rotors to resist fast time-varying uncertainty. Given the constrained amplitude of powered yaw control, it is imperative that the designed auxiliary input guarantees adherence to its constraint. Firstly, a nonlinear control for nominal hybrid unmanned aerial vehicle system is formulated to deal with the nonlinearity model, rendering a modest nominal control for rudders. Secondly, powered yaw control is proposed to effectively resist fast time-varying uncertainty by harnessing the faster response of rotors, while simultaneously considering the constrained amplitude of powered yaw control. Stability and robust of the hierarchical yaw control are proved under fast time-varying uncertainty and constrained powered yaw control by the Lyapunov analysis using uniform boundedness and uniform ultimate boundedness. Simulations are performed, comparing to other control methods, demonstrating the effectiveness of the proposed control method under fast time-varying uncertainty and inputs constraint.