Search

In this article, we introduced a novel definition for a class of extended Nussbaum functions that have looser requirements than the traditional Nussbaum function. The extended Nussbaum function achieves comparable performance to the traditional Nussbaum function while addressing the challenges of unknown control directions and time‐varying actuator faults. We then provide a specific example function based on the extended Nussbaum function definition. Unlike the traditional Nussbaum function, which oscillates with fixed frequency and constantly increasing amplitude, this example function constrains the amplitude and oscillates with decreasing frequency. Consequently, its amplitude and derivative remain bounded. The oscillation of the system caused by the too large amplitude of the traditional Nussbaum function can be avoided. Furthermore, this example function is constructed using portions of elliptic curve. As a result, it is continuous and differentiable, in contrast to the normal decreasing‐frequency Nussbaum function using trigonometric function, which is only continuous. The overall closed‐loop system's global stability and asymptotic convergence of system states are successfully achieved. Simulation results demonstrate the effectiveness of the proposed function. [ABSTRACT FROM AUTHOR]

This article studies the leader‐following attitude coordination problem of a group of rigid spacecraft subject to communication constraint, disturbances and uncertain control coefficient matrices. A fully distributed adaptive anti‐disturbance attitude coordinated control scheme with event‐triggering mechanism is developed. First, the event‐triggered adaptive distributed observer is designed for each follower to estimate the leader's information without continuous communication requirement. Based on the estimated information, the adaptive anti‐disturbance attitude tracking controller is designed such that asymptotic coordinated tracking can be achieved under additive disturbances and actuators' partial loss of efficiency. The proposed control scheme ensures that all the closed‐loop signals are bounded and the positive lower bound of inter‐event times exists in each subsystem. Simulation results illustrate the effectiveness and flexibility of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper concerns about the safe approaching in rendezvous with spherical envelops of spacecraft. Based on the nonnegative characteristic of positive systems, a novel strategy of controlling the relative distance positive and convergent is proposed to guarantee no‐collision approaching. The dynamics of the relative distance is decoupled from that of the relative angles. A nonlinear disturbance observer is designed, and two anti‐disturbance controllers are constructed to reject the effect of disturbances for the subsystems of relative distance and angles. Under the controllers, the closed‐loop subsystem of relative distance is a positive and stable system, while that of relative angles is a general stable system satisfying the given time‐varying constraints. Particularly, a theorem is proposed to present the conditions of controllers to ensure the system positivity under a class of external inputs without nonnegativity default. Finally, simulation results are presented to illustrate the effectiveness of proposed methods. [ABSTRACT FROM AUTHOR]

In this article, we propose a novel event‐triggered control (ETC) method from the control input perspective. Different from existing results in which event conditions are designed based on the variation of system states, this method designs event conditions from the control input perspective, that is, based on the control input variations. Through this method, it is shown that for nonlinear systems, the commonly used input‐to‐state stable assumption can be removed. For linear systems, this method is shown equivalent to conventional results established based on state signals. Moreover, it provides flexibility in designing different event conditions for uncertain nonlinear systems. The effectiveness of the proposed method is demonstrated through two simulation examples. [ABSTRACT FROM AUTHOR]

Robustness of positive systems with respect to disturbances is a challenging issue of both theoretical and practical importance. In this study, the stabilisation control problem of positive systems with disturbances is investigated. More generalised disturbances are considered here, including positive modelled disturbances and general disturbances. A disturbance observer is designed to estimate the disturbances and a sufficient and necessary condition for stabilisation is derived. For positive disturbances, a sufficient condition with the use of the convergence law for the existence of controller is proposed, and this problem can be formulated as a linear programming problem. Furthermore, the corresponding theory is expanded to generally modelled disturbances, which enriches the theories about anti‐disturbance control of positive systems. Meanwhile, the analysis is given in detail to promote the theoretical completeness, including conservations of hypothesis and positivity constraints of disturbance estimation values. Simulation results show that the proposed scheme can guarantee the positivity of systems and improve the system performances for generalised disturbances. [ABSTRACT FROM AUTHOR]

In this paper, an output-feedback adaptive consensus tracking control scheme is proposed for a class of high-order nonlinear multi-agent systems. The agents are allowed to have unknown parameters, unknown nonlinearities, and input quantization simultaneously. The desired trajectory to be tracked is available for only a subset of agents, and only the relative outputs and the quantized inputs need to be measured or transmitted as signal exchange among neighbors regardless of the system order. By introducing a kind of high-gain K-filters and a smooth function, the effect among agents caused by the unknown nonlinearities is successfully counteracted, and all closed-loop signals are proved to be globally uniformly bounded. Moreover, it is shown that the tracking errors converge to a residual set that can be made arbitrarily small. Simulation results on robot manipulators are presented to illustrate the effectiveness of the proposed scheme. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, a new adaptive compensation control scheme is proposed for a class of nonlinear systems with unknown parameters and unknown actuator failures. The normal operation case and different failure cases of actuators are unified through a time-varying model. By introducing a smooth function, an integrable auxiliary signal, and a bound estimation approach, the effect of failures is successfully compensated for, and the total number of failures is not restricted to be finite. It is shown that all closed-loop signals are globally uniformly bounded, and the tracking error converges to zero asymptotically regardless of the possibly infinite number of actuator failures. An application to the longitudinal dynamic model of a twin otter aircraft is presented to illustrate the effectiveness of the proposed scheme. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The design of output constrained control system for unmanned aerial vehicles deployed in confined areas is an important issue in practice and not taken into account in many autopilot systems. In this study, the authors address a neural networks‐based adaptive trajectory tracking control algorithm for multi‐rotors systems in the presence of various uncertainties in their dynamics. Given any sufficient smooth and bounded reference trajectory input, the proposed algorithm achieves that (i) the system output (Euclidean position) tracking error converges to a neighbourhood of zero and furthermore (ii) the system output remains uniformly in a prescribed set. Instead of element‐wise estimation, a norm estimation approach of unknown weight vectors is incorporated into the control system design to relieve the onboard computation burden. The convergence property of the closed‐loop system subject to output constraint is analysed via a symmetric barrier Lyapunov function augmented with several quadratic terms. Simulation results are demonstrated on a quadrotor model to validate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper is devoted to adaptive output tracking for a class of multi-input multi-output nonlinear systems with unknown non-symmetric dead-zone. With the aid of a matrix factorization and a similarity transformation, a robust adaptive dynamic surface control scheme is proposed and the difficulty caused by the control gain matrix and the dead-zone is circumvented. By introducing a surface error modification and an initialization technique, we show that the [ABSTRACT FROM AUTHOR]

SUMMARY This paper is devoted to output-feedback adaptive control for a class of multivariable nonlinear systems with both unknown parameters and unknown nonlinear functions. Under the Hurwitz condition for the high-frequency gain matrix, a robust adaptive backstepping control scheme is proposed, which is able to guarantee the [ABSTRACT FROM AUTHOR]