Search

Summary To enhance the convergent rate and robustness of buck-type DC-DC converter system, a new finite-time voltage regulation control algorithm is proposed in this paper. First, an average state space-based model is analyzed, which considers both the parameters uncertainties and the variations of load and input voltage. By using saturation finite-time control theory, at the first step, in the absence of disturbance, a new fast voltage regulation control algorithm is designed, which can guarantee that the output voltage converges to the reference voltage in a finite time. Because the saturation constraint is considered during the controller design, the duty ratio function of the converter satisfies the constraint between 0 and 1. Second, in the presence of disturbance, a finite-time convergent disturbance observer is designed to estimate the unknown disturbances in a finite time. Finally, a disturbance observer-based finite-time voltage regulation control algorithm is developed. Compared with PI (Proportional-Integral) control algorithm, circuit simulations show that the proposed algorithm has a faster regulation performance and stronger robustness performance on disturbance rejection.

Summary In this paper, robust containment problem is investigated for a class of multi-leader multi-agent linear systems in the presence of time-varying uncertainties. To achieve containment, a new kind of adaptive containment protocols are proposed for the multi-agent systems. Specifically, the designed protocols consist of a continuous linear term and a discontinuous term. The linear term of the designed protocol is employed to achieve containment while the discontinuous term is utilized to eliminate the effect of uncertain dynamics on the achievement of containment. By using tools from non-smooth analysis and algebraic graph theory, some efficient criteria for achieving robust containment in the closed-loop multi-agent systems are obtained and analyzed. One favorable property of the designed protocol is that containment in the closed-loop multi-agent systems can be achieved in a fully distributed fashion over any given connected and detail-balanced communication graph without using any global information about the communication graph. The effectiveness of the analytical results is finally verified by performing numerical simulations. Copyright © 2016 John Wiley & Sons, Ltd.

Summary This paper studies the distributed average computation problem for multiple time-varying signals with bounded inputs. Based only on relative output measurements, a pair of continuous algorithms with, respectively, static and adaptive coupling strengths are designed and utilized. From the concept of boundary layer approach, the proposed continuous algorithm with static coupling strengths can asymptotically obtain the average value of the multiple reference signals without chattering phenomenon. Furthermore, for the case of algorithms with adaptive coupling strengths, the calculation errors are uniformly ultimately bounded and exponentially converge to a small adjustable bounded set. Finally, a simulation example is presented to show the validity of the theoretical results. Copyright © 2015 John Wiley & Sons, Ltd.

Summary This paper studies a distributed coordinated control problem for a class of linear multi-agent systems subject to two types of attacks. The problem boils down to how to achieve secure consensus tracking for multi-agent systems with connected and disconnected (paralyzed) directed switching topologies caused by two types of attacks. The attacks on the edges instead of nodes lead to the loss of security performance. Two cases are studied in this paper. First, under only a class of connectivity-maintained attacks, sufficient conditions are derived to achieve secure consensus tracking in mean-square. Second, when the multi-agent systems are further subject to a class of connectivity-broken attacks, novel sufficient conditions are further obtained to ensure secure consensus tracking with a specified convergence rate by virtue of the idea of average dwell time switching between some stable and unstable subsystems. Three numerical simulations are finally given to illustrate the theoretical analysis. Copyright © 2015 John Wiley & Sons, Ltd.

Summary This paper is concerned with the mean square node-to-node consensus tracking problem for multi-agent systems with nonidentical nonlinear dynamics and directed topologies. The randomly occurred uncertainties in the sampling devices may result in stochastically varied sampling periods, which lead to the investigation of node-to-node consensus problem under stochastic sampling. By employing the input-delay method and discontinuous Lyapunov functional approach, it arrives at some sufficient conditions under which the state of each follower can track that of the corresponding leader asymptotically in the mean square sense. Finally, some numerical simulations are provided to verify the effectiveness of the theoretical results. Copyright © 2015 John Wiley & Sons, Ltd.

Summary Distributed coordinated tracking problems are investigated in this paper for a class of multi-agent dynamical systems with general linear node dynamics under a directed fixing interaction topology. First, a kind of class of distributed information communication protocols based on only the relative output measurements of neighboring agents is proposed and employed to realize containment tracking in multi-leader multi-agent linear systems. With the assumptions that the intrinsic linear dynamics of each agent are stabilizable and detectable, and each follower can be directly or indirectly affected by at least one leader, it is proven that containment tracking in the closed-loop multi-leader multi-agent systems will be guaranteed if the coupling strength between neighboring agents and the gain matrices of the information communication protocols are suitably chosen. The decay rate for containment tracking errors of the considered multi-leader multi-agent system is also discussed. Then, consensus tracking and formation control problems of single-leader multi-agent systems with general linear node dynamics are respectively addressed. At last, node-to-node consensus tracking for multi-agent systems with multiple coupling leaders is discussed. Simulation examples and experiment results are performed to validate the obtained results. Copyright © 2017 John Wiley & Sons, Ltd.

This paper investigates the consensus tracking problem for both continuous- and discrete-time multi-agent systems with general linear dynamics and stochastic disturbances under a global detectability condition. It is assumed that there exists a dynamic leader and the subgraph describing the communication topology among the followers is undirected and connected. The proposed global detectability condition extends the traditional local detectability condition to the networked case. By using the relative states of neighboring followers and the relative measurement information of the leader, distributed observer-type consensus protocols are constructed for both continuous- and discrete-time cases to guarantee all the followers to track the leader. A distinct feature of this paper is that the relative states of the leader are estimated by a group of followers rather than any individual follower. It is found that the mean square tracking errors are bounded even if the leader is not detectable by any follower, where the only requirement is that the leader is globally detectable by followers. Simulation results are finally presented to verify the effectiveness of theoretical results.

Summary In this paper, the distributed H ∞ robust control problem synthesized with transient performance is investigated for a group of autonomous agents governed by uncertain general linear node dynamics. Based on the relative information between neighboring agents and some information of other agents, distributed state-feedback and observer-type output-feedback control protocols are designed and analyzed, respectively. By using tools from robust control theory, conditions for the existence of controllers for solving such a problem are established. It is shown that the problem of distributed H ∞ robust control synthesized with transient performance can be converted to the H ∞ control problem synthesized with transient performance for decoupled linear systems of the same low dimensions. Finally, simulation examples are provided to illustrate the effectiveness of the design. Copyright © 2014 John Wiley & Sons, Ltd.

Summary This paper investigates the distributed finite-time tracking problem of networked agents with multiple Euler–Lagrange dynamics. To achieve finite-time tracking, a distributed finite-time protocol is first proposed on the basis of both relative position and relative velocity measurements. By using tools from homogeneous theory, it is theoretically shown that the proposed protocol can guarantee finite-time tracking in the presence of control input constraints. On the basis of the state feedback analysis and with the aid of second-order sliding-mode observer approach, a new class of finite-time tracking protocols based only on the relative position measurements is developed and employed. It is proved that the multiple agents equipped with the designed protocols can track the target location in finite time. Furthermore, a decentralized finite-time protocol based on a distributed estimator is proposed to solve the finite-time tracking problems with a dynamic leader. The effectiveness of the theoretical results is finally illustrated by numerical simulations. Copyright © 2014 John Wiley & Sons, Ltd.

In this paper, an anti-windup bumpless transfer (AWBT) control structure combined with linear interpolation method is proposed for smooth switching control. By choosing an appropriate scheduling signal, different controllers can be switched smoothly under a unified framework. Meanwhile, some robust specifications including H2/H∞ performance, pole placement constraint, and passivity of the closed-loop system can be preserved through controller switching. Furthermore, for the linear system subject to input saturation, the stability and L2 gain of the closed-loop system can be guaranteed. Finally, a cart-spring pendulum system is simulated to demonstrate the effectiveness of the proposed scheme.

SUMMARY Without assuming that the mobile agents can communicate with their neighbors all the time, the consensus problem of multi-agent systems with general linear node dynamics and a fixed directed topology is investigated. To achieve consensus, a new class of distributed protocols designed based only on the intermittent relative information are presented. By using tools from matrix analysis and switching systems theory, it is theoretically shown that the consensus in multi-agent systems with a periodic intermittent communication and directed topology containing a spanning tree can be cast into the stability of a set of low-dimensional switching systems. It is proved that there exists a protocol guaranteeing consensus if each agent is stabilizable and the communication rate is larger than a threshold value. Furthermore, a multi-step intermittent consensus protocol design procedure is provided. The consensus algorithm is then extended to solve the formation control problem of linear multi-agent systems with intermittent communication constraints as well as the consensus tracking problem with switching directed topologies. Finally, some numerical simulations are provided to verify the effectiveness of the theoretical results. Copyright © 2013 John Wiley & Sons, Ltd.

The consensus problem is investigated in this paper for a class of multi-agent systems with general linear node dynamics and directed communication topologies. A new distributed observer-type consensus protocol is designed based only on the relative output measurements of neighboring agents. Compared with existing observer-type protocols, the one presented here does not require information about the relative states of the observers. Tools from small gain theory and matrix analysis, some sufficient conditions are obtained for achieving consensus in such multi-agent systems where the underlying network topology contains a directed spanning tree. Finally, some numerical examples including an application in low-Earth-orbit satellite formation flying are provided to illustrate the theoretical results.

SUMMARY This paper is concerned with the problem of consensus in directed networks of multiple agents with intrinsic nonlinear dynamics and sampled-data information. A new protocol is induced from a class of continuous-time linear consensus protocols by implementing data-sampling technique and a zero-order hold circuit. On the basis of a delayed-input approach, the sampled-data multi-agent system is converted to an equivalent nonlinear system with a time-varying delay. Theoretical analysis on this time-delayed system shows that consensus with asymptotic time-varying velocities in a strongly connected network can be achieved over some suitable sampled-data intervals. A multi-step procedure is further presented to estimate the upper bound of the maximal allowable sampling intervals. The results are then extended to a network topology with a directed spanning tree. For the case of the topology without a directed spanning tree, it is shown that the new protocol can still guarantee the system to achieve consensus by appropriately informing a fraction of agents. Finally, some numerical simulations are presented to demonstrate the effectiveness of the theoretical results and the dependence of the upper bound of maximal allowable sampling interval on the coupling strength. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY In this paper, the problem of flocking control in networks of multiple dynamical agents with intermittent nonlinear velocity measurements is studied. A new flocking algorithm is proposed to guarantee the states of the velocity variables of all the dynamical agents to converge to consensus while ensuring collision avoidance of the whole group, where each agent is assumed to obtain some nonlinear measurements of the relative velocity between itself and its neighbors only on a sequence of non-overlapping time intervals. The results are then extended to the scenario of flocking with a nonlinearly dynamical virtual leader, where only a small fraction of agents are informed and each informed agent can obtain intermittent nonlinear measurements of the relative velocity between itself and the virtual leader. Theoretical analysis shows that the achieved flocking in systems with or without a virtual leader is robust against the time spans of the agent speed-sensors. Finally, some numerical simulations are provided to illustrate the effectiveness of the new design. Copyright © 2011 John Wiley & Sons, Ltd.

The problem of second-order consensus is investigated in this paper for a class of multi-agent systems with a fixed directed topology and communication constraints where each agent is assumed to share information only with its neighbors on some disconnected time intervals. A novel consensus protocol designed based on synchronous intermittent local information feedback is proposed to coordinate the states of agents to converge to second-order consensus under a fixed strongly connected topology, which is then extended to the case where the communication topology contains a directed spanning tree. By using tools from algebraic graph theory and Lyapunov control approach, it is proved that second-order consensus can be reached if the general algebraic connectivity of the communication topology is larger than a threshold value and the mobile agents communicate with their neighbors frequently enough as the network evolves. Finally, a numerical example is simulated to verify the theoretical analysis. Copyright © 2011 John Wiley & Sons, Ltd.