910 publications from this institution
The generalized Jang equation was introduced in an attempt to prove the Penrose inequality in the setting of general initial data for the Einstein equations. In this paper we give an extensive study of this equation, proving existence, regularity, and blow-up results. In particular, precise asymptotics for the blow-up behavior are given, and it is shown that blow-up solutions are not unique.
This paper is concerned with the robust H∞ control problem for linear uncertain systems with multiple time-varying delays. Based on the linear matrix inequality (LMI) approach, we develop a method for synthesizing a robust H∞ dynamic output feedback control law which guarantees the quadratic stability of the closed-loop system and reduces, to a prescribed level, the effect of the disturbance input on the controlled output. A sufficient condition for the existence of a robust H∞ controller of any order is proposed in terms of three LMIs. One can easily design a robust H∞ controller by solving the three LMIs numerically very efficiently via convex and quasi-convex optimization techniques.
Distributed networked control systems have attracted intense attention from both academia and industry due to the multidisciplinary nature among the areas of communication networks, computer science and control. With ever-increasing research trends in these areas, it is desirable to review recent advances and to identify methodologies for distributed networked control systems. This paper presents a brief overview of such systems regarding system configurations, challenging issues and methodologies. First, networked control systems are introduced and their prevalent configurations including centralized, decentralized and distributed structures are outlined. Second, an emphasis is laid on a number of challenging issues from the analysis and synthesis of distributed networked control systems. More specifically, these challenging issues are identified through three integrated aspects: communication, computation and control. Third, different methodologies in the literature for distributed networked control systems are reviewed and categorized based on three pairs: undirected and directed graphs, fixed and time-varying topologies, and time-triggered and event-triggered mechanisms. Finally, concluding remarks are drawn and some potential research directions are suggested.
This paper is concerned with the networked cooperative path following (CPF) problem for multiple autonomous surface vehicles (ASVs) subject to simultaneous cyber and physical attacks. First, to compensate the adverse effects of the physical-attack-induced bias injections, an extended state observer is designed to provide real-time estimates of the unmeasured velocities and unknown nonlinear terms. Next, to identify and handle various cyber attacks, a novel secure data transmission mechanism, featuring a secure transmitter and a secure receiver, is developed for each ASV. Then, a secure CPF control scheme, consisting of a networked cooperative kinematic control law and a networked kinetic control law, is presented. Furthermore, the observer error dynamics and networked CPF error dynamics are derived to account for the simultaneous network-induced delays, packet dropouts, physical attacks, and cyber attacks. The proposed control scheme is capable to preserve satisfactory secure tracking performance of the resulting CPF control system under a desired reference path even in the presence of external environmental disturbances, delays, packet dropouts, and malicious attacks. Finally, several case studies are provided to substantiate the effectiveness of the secure CPF control scheme.
This paper is concerned with sliding mode H ∞ control for an offshore steel jacket platform subject to nonlinear self-excited wave force and external disturbance. A sliding mode H ∞ controller is designed to reduce the oscillation amplitudes of the offshore platform. In the case that the dynamic model of the offshore platform is subject to parameter perturbations, a robust sliding mode H ∞ control scheme is proposed. It is found through simulation results that (i) compared with an H ∞ controller and a sliding mode controller, the sliding mode H ∞ controller requires much less control force, and (ii) the oscillation amplitudes of the offshore platform under the sliding mode H ∞ controller are less than those under the sliding mode controller.
Industrial cyber-physical systems (CPSs) are large-scale, geographically dispersed, and life-critical systems, in which lots of sensors and actuators are embedded and networked together to facilitate real-time monitoring and closed-loop control. Their intrinsic features in geographic space and resources put forward to urgent requirements of reliability and scalability for designed filtering or control schemes. This paper presents a review of the state-of-the-art of distributed filtering and control of industrial CPSs described by differential dynamics models. Special attention is paid to sensor networks, manipulators, and power systems. For real-time monitoring, some typical Kalman-based distributed algorithms are summarized and their performances on calculation burden and communication burden, as well as scalability, are discussed in depth. Then, the characteristics of non-Kalman cases are further disclosed in light of constructed filter structures. Furthermore, the latest development is surveyed for distributed cooperative control of mobile manipulators and distributed model predictive control in industrial automation systems. By resorting to droop characteristics, representative distributed control strategies classified by controller structures are systematically summarized for power systems with the requirements of power sharing and voltage and frequency regulation. In addition, distributed security control of industrial CPSs is reviewed when cyber-attacks are taken into consideration. Finally, some challenges are raised to guide the future research.
This paper is concerned with the problem of event-triggered H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control for a class of networked control systems with nonlinear perturbations. The nonlinear perturbations appear in both the system dynamic equation and the controlled output signals. An event-triggered transmission scheme is introduced to select `necessary' sampled-data packets to be transmitted through a communication network. Under the event-triggered transmission scheme, the closed-loop system is modeled as a system with an interval time-varying delay. Employing the matrix-based quadratic convex approach recently reported in the literature, a novel sufficient condition on the existence of desired event-triggered H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controllers is derived in terms of solutions to a set of linear matrix inequalities. No parameters need to be tuned when controllers are designed. Finally, a numerical example is given to demonstrate the effectiveness of the proposed method.
This paper addresses an event-based consensus problem for a continuous-time nonlinear multi-agent system subject to communication resource constraints. The agents' states are measured by a multi-sensor network, in which sensor nodes are dispersedly deployed in a sensor field. Each sensor node can gather information from its neighboring nodes, process aggregated information by a prescribed network topology, sample processed information at a synchronous sampling period and then transmit sampled information to a remote controller node via a shared network medium. First, to reduce the frequency of transmitting sensors' sampled-data, an event-based communication strategy is presented to schedule sensors' data transmission. Second, based on transmitted aggregated measurement, a delicate event-based consensus protocol is proposed. Compared with some existing event-based consensus protocols based on transmitted local measurement, the proposed protocol offers some advantages. Third, a criterion for designing desired event-based consensus protocol and event triggering strategy is provided such that the proposed event-based consensus is achieved. It is shown that the consensus protocol gain and the event strategy threshold parameter can be jointly determined by solving a Riccati inequality. Finally, a vertical taking-off and landing aircraft model is employed to show the effectiveness of the proposed result.
This paper is concerned with an event-triggered hybrid control for the energy Internet based on a multi-agent system approach with which renewable energy resources can be fully utilized to meet load demand with high security and well dynamical quality. In the design of control, a multi-agent system framework is first constructed. Then, to describe fully the hybrid behaviors of all distributed energy resources and logical relationships between them, a differential hybrid Petri-net model is established, which is an original work. The most important contributions based on this model propose four types of event-triggered hybrid control strategies whereby the multi-agent system implements the hierarchical hybrid control to achieve multiple control objectives. Finally, the effectiveness of the proposed control is validated by means of simulation results.
In this paper, the cooperative dynamic positioning (CDP) of multiple unmanned surface vehicles (multi-USVs) is studied in network environments. Firstly, networked cooperative dynamic positioning system (CDPS) models are constructed for multi-USVs subject to disturbance induced by wind, waves, and current. Secondly, considering the negative influences of network-induced delays, a CDP control protocol is designed. Then, by employing Lyapunov-Krasovskii approach, a controller design criterion ensuring CDP is derived such that the errors of earth-fixed position and heading between unmanned surface vehicles (USVs) and a reference state vector converge to a bounded region. Finally, the performance analysis verifies the effectiveness of the design approach presented in this paper.
