This paper proposes a disturbance interval estimation approach for nonlinear systems. Distinct from the conventional estimation schemes aiming to estimate the magnitude of the disturbance, the disturbance interval estimation approach is capable of approximating the time-varying upper and lower boundaries for the disturbance. To achieve this, the dynamics of the boundary estimation errors are constructed as positive systems by introducing a time-invariant coordinate transformation. The boundary estimation errors are guaranteed to be nonnegative and bounded. Then, the generated interval is capable of covering all possible values of the current disturbance and the interval width can provide a quantized guidance on the estimation accuracy at any time. Furthermore, a general antidisturbance control scheme is summarized in light of the proposed disturbance interval estimation approach. As an illustrative case, an antidisturbance control method is developed by integrating the proposed estimation approach and the sliding mode control. Finally, the proposed disturbance interval estimation approach and the anti-disturbance control method are demonstrated through both the numerical and the experimental validation.

This article studies a cooperative time-varying formation of underactuated unmanned surface vehicles (USVs) with position-heading measurements, following the philosophies of (i) balance operation between performance constraints and safety requirements including collision avoidance and connectivity maintenance, and (ii) concise finite-time control design based on the integrated finite-time extended state observer (IFTESO) to facilitate the practical implementation. At first, to accomplish the guidance design of networked vehicles in the complex ocean environment and guarantee the performance of cooperative tracking errors, a flexible performance-based control scheme is investigated by feeding the potential effects of safety requirements into the modification signals of the user-specified performance functions. Then, without the application of cumbersome nonlinear tracking differentiators and backstepping techniques, a output-feedback IFTESO-based method provides a concise solution with a convenient design by taking advantage of homogeneous system theories, which further reduces the traditional computation consumption. Finally, the performance of the proposed scheme is validated by numerical simulations.

Addressing external disturbances has been a critical issue for control design to ensure reliable operation of systems. This article investigates the tracking control problem for the uncertain nonlinear systems with the strong external disturbance and the prescribed performance. The flexible performance-based control scheme is developed by introducing an external disturbance criterion into the prescribed performance. It is capable of guaranteeing the prescribed performance if the external disturbance is less than a specified threshold and degrading that in light of the user-appointed rule otherwise. Particularly, the disturbance interval observer is synthesized to generate the boundaries of the external disturbances and realize the judgment of that criterion. With the generated boundaries, the interval-type auxiliary system is designed to provide the modified performance functions (MPFs) that characterize performance requirement and degradation rule simultaneously. Based on the positive system theory and the Lyapunov method, it is theoretically shown that the system output can always track the reference signal and satisfy the constraints of MPFs. Finally, both the numerical simulation and the application of flight control design verify that the results are effective and valid.

In this article, an anti-disturbance control design is presented for nonlinear systems based on a hybrid disturbance estimation scheme. This scheme features the capability of making full use of the incomplete knowledge on disturbance dynamics. By embedding the known information, the disturbance interval observer is developed to generate boundaries to cover individually each element of external disturbances. Through synthesizing a tangent barrier Lyapunov function-based estimation switching mechanism, the modified disturbance observer is proposed to take appropriate values between the boundaries as the estimation. By using this estimation, the anti-disturbance control compensates for external disturbances. It is proved that the system states stay within a specified region and converge to a small neighborhood of the origin. Finally, the numerical simulation is presented to illustrate the effectiveness and benefits of the estimation scheme and the control design.

In this work, the flexible performance-based control scheme is presented for the networked uncertain mechanical system under the quasi-periodic denial-of-service (DoS) attack and the appointed event-triggering (ET) mechanism. This scheme features the capability of releasing and recovering the prescribed performance in light of the activation and sleeping of the DoS attack. These functionalities attribute to the introduction of a self-regulation auxiliary system that is developed based on the theories of the positive system and the finite-time stability. Furthermore, the neural network (NN) is utilized to approximate the system uncertainty, and the noncertainty-equivalent structure is adopted to construct the update law of the NN. Then, the influence of the quasi-periodic DoS attack and the appointed ET mechanism on uncertainty approximation are totally isolated. Based on the Lyapunov function method and the invariant set theory, the boundedness of the closed-loop system is theoretically proved. Finally, both the numerical and experimental illustrations are presented to demonstrate the effectiveness and the benefits of the developed control scheme.