Resilient Control Strategy for a VTOL UAV Achieving Safe Transition Flight Under Actuator Faults and Disturbances

Hybrid Vertical Takeoff and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) demonstrate more flexible advantages in complex missions due to their capability to VTOL and conduct high-speed horizontal flight. But their ability to achieve safe transition flight still remains a challenge. This paper proposes a resilient transition control strategy for a VTOL UAV under the compounded impact of actuator faults and disturbances. A novel reaching law is introduced in the baseline sliding mode control (SMC) to mitigate the control chattering problem, and SMC is incorporated with a nonlinear disturbance observer to enhance the attenuation capability of external disturbances. On this basis, adaptive SMC is introduced to compensate for adverse effect caused by actuator faults and disturbances. The designed adaptive parameters combine continuous and discontinuous components without merely relying on the discontinuous control parts of SMC. Simulation test is finally carried out to qualitatively and quantitatively validate the superiority of the proposed method.