Multivariable Disturbance Observer-Based Finite-Time Sliding Mode Attitude Control for Fixed-Wing UAVs Under Matched and Mismatched Disturbances

In this letter, we propose a multivariable disturbance observer-based finite-time sliding mode attitude control (MDOB-FT-SM-AC) for fixed-wing UAVs in the presence of both matched and mismatched disturbances. Compared with existing sliding mode attitude controllers, the significant improvements of the proposed MDOB-FT-SM-AC are the multivariable control structure, strong robustness, and high precision performance with continuous control input signal. In the proposed MDOB-FT-SM-AC, we first develop multivariable finite-time disturbance observers such that the precise estimation of both matched and mismatched disturbances is ensured. Next, a nonsingular terminal sliding manifold is designed such that the fixed-wing UAV is driven to track its desired attitude command in finite time. We finally present a multivariable super-twisting reaching law such that the finite-time convergence of the sliding variable and its derivative to zero is guaranteed. Attentive finite-time convergence analysis is derived based on the Lyapunov and homogeneity theories. Simulation results are given to illustrate the superiority of the proposed MDOB-FT-SM-AC.