Trajectory Tracking Control of A Quadrotor UAV by Cascaded Inner-Outer-Loop Backstepping Sliding Mode Control

In this paper, a cascaded inner-outer-loop backstepping sliding mode control method is proposed to solve the trajectory tracking problem for a quadrotor UAV. In the control structure, attitude tracking control loop is considered as an inner loop while position control loop is served as an outer loop. The sliding mode control approach is introduced to stabilize the inner attitude control loop, while the backstepping sliding mode control approach is adopted to stabilize the outer trajectory tracking control loop and inversely solve the nonlinear equation to obtain the results of total throttle thrust and reference attitude angles with a virtual control vector, to address the coupling problem between total throttle thrust and attitude angles by trigonometric function. Compared with the traditional approximation method such as "small perturbation" linearization in a trimming state, the backstepping method is more accurate and direct. The proposed backstepping sliding mode control approach is validated by numerical simulations on a quadrotor UAV and simulation results indicate that the proposed control strategy is stable and effective with acceptable performance.