Nonsingular sliding mode trajectory tracking control for quadrotor unmanned aerial vehicles based on nonlinear disturbance observer

To address the trajectory tracking problem of quadrotor unmanned aerial vehicle (UAV) in complex flight environments, this paper proposes a nonsingular terminal sliding mode control method based on a novel multi-power reaching law. Combined with a composite disturbance observer, this method achieves accurate estimation and active compensation of external disturbances. First, a six-degree-of-freedom dynamic model of the UAV is established, accounting for air resistance and external disturbances. A dual-loop cascade control architecture is employed to decouple the position and attitude loops. Second, a linear extended state observer and a nonlinear disturbance observer are designed for the position and attitude loops, respectively, constructing a composite observation strategy to improve the accuracy and robustness of disturbance estimation. Next, a nonsingular terminal sliding mode surface based on multi-power terms is designed, and a novel multi-power reaching law is proposed. This reaching law incorporates linear, high-order, and low-order power terms, as well as an adaptive hyperbolic function. The reaching law form is adaptively adjusted based on the sliding surface, ensuring rapid convergence while effectively mitigating the chattering phenomenon of traditional sliding mode control. Finally, the stability and finite-time convergence characteristics of the closed-loop system are demonstrated using Lyapunov stability theory. The simulation results show that the proposed control method can achieve high-precision trajectory tracking under the action of time-varying composite disturbances, which verifies the effectiveness of the method proposed in this paper.