Continuous Nonsingular Terminal Sliding-Mode Control With Integral-Type Sliding Surface for Disturbed Systems: Application to Attitude Control for Quadrotor UAVs Under External Disturbances

This article proposes a continuous nonsingular terminal sliding-mode control with integral-type sliding surface (CNTSMC-ISS) framework for disturbed systems, in which we consider two types of finite-time controllers: the state feedback CNTSMC-ISS and the disturbance-observer-based CNTSMC-ISS. Compared with the existing sliding-mode controllers, the noteworthy contributions of two finite-time controllers in the proposed CNTSMC-ISS framework are the alleviation of the chattering phenomenon, the fast finite-time stability, and the singularity-free and ease-of-implementation characteristics. In the proposed CNTSMC-ISS framework, we first introduce a nonsingular integral terminal sliding-mode surface (NITSMS) such that the finite-time convergence of the system states to zero in the sliding phase is ensured and the singularity problem is avoided. Besides, a finite-time observer is developed to recover the external disturbance. Then, based on the constructed NITSMS with the supertwisting-like algorithm, the state feedback CNTSMC-ISS and the disturbance-observer-based CNTSMC-ISS are proposed, which generate the continuous control signals and guarantee the fast finite-time convergence of the system states to the designed sliding surface. Rigorous finite-time stability of the closed-loop system under two proposed controllers is provided. Finally, we apply two finite-time controllers in the proposed CNTSMC-ISS framework to the attitude control for quadrotor unmanned aerial vehicles under external disturbances. Extensive simulation and experimental results are illustrated to prove the effectiveness of the proposed attitude controllers.