Multi‐variable finite‐time observer‐based adaptive‐gain sliding mode control for fixed‐wing UAV
Chaofan Zhang, Guoshan Zhang, Qi Dong
Abstract
Abstract This paper presents a multivariable finite‐time observer‐based adaptive‐gain sliding mode control scheme for a fixed‐wing unmanned aerial vehicle (UAV) subject to the unmeasurable angular rates and unknown matched/unmatched disturbance. The control‐oriented model is obtained through the dynamics of fixed‐wing UAV and is composed of attitude subsystem and airspeed subsystem. For the attitude subsystem, a multi‐variable finite‐time observer (MFO) is constructed to achieve the estimation values of unknown states. With the estimation values provided by MFO, a novel adaptive dual‐layer continuous terminal sliding mode (ADL‐CTSM) controller is proposed to track the reference attitude command in finite time. The advantage of the proposed ADL‐CTSM controller is that the bounds of the disturbances are not required and the adaptive gains are obtained as small as possible to attenuate chattering efficiently. For the airspeed subsystem, the tracking differentiator (TD), which enhances the tracking performance, is employed to obtain the smooth reference command and its derivative. The Lipschitz continuous control signal is generated by the designed airspeed controller which is based on the linear proportional‐integral (PI) and the integral of the adaptive‐dual layer twisting algorithm (PIATCI). The rigorous proof of the finite‐time stability of the close‐loop system is provided through Lyapunov criteria and homogeneous technique. Finally, three cases of simulations are carried out to verify the effectiveness and superiority of the proposed control scheme.