Lu Liu

Lu Liu
University of Macau

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248
Publications
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Publications

Publications (248)
Article
This paper addresses the safe cooperative path following for multiple autonomous surface vehicles (ASVs) in the presence of static and dynamic obstacles. The positions and velocities of the obstacles are unknown, and only the relative angle is measured. The ASVs are subject to uncertain kinetics and unknown disturbances induced by wind, waves and c...
Article
This paper presents a cooperative vector field approach for synchronized path following of multiple autonomous surface vehicles (USVs) with limited communication resources. First, a cooperative vector field is proposed by introducing a path coordination design into a three-dimensional vector field. Based on the cooperative vector field, concise gui...
Article
This article studies the tracking problem of a class of heterogeneous linear minimum-phase discrete-time multiagent systems (MASs) with unknown agent parameters in the presence of bounded disturbances. By introducing a distributed adaptive observer and a reference model, a novel framework is proposed to convert the complicated cooperative tracking...
Article
This article deals with the leader-following consensus problem of multiple uncertain Euler-Lagrange systems with unknown nonlinear dynamics. By introducing a dynamic compensator for each agent, a fully distributed control strategy is developed based on the fuzzy approximation approach, which is independent of any priori global information associate...
Article
This paper is concerned with the resilient speed control of an autonomous surface vehicle (ASV) in the presence of actuator anomalies. A data-driven model-free resilient speed control method is presented based on available input and output data only with pulse-width-modulation inputs. Specifically, a data-driven neural predictor is designed to lear...
Article
This paper addresses the formation reconfiguration problem of multiple unmanned surface vehicles subject to static and dynamic obstacles. Specifically, a desired heading is prescribed based on a guiding vector field for pointing the target while avoiding static obstacles. Fixed-time control Lyapunov and barrier function are employed to steer each U...
Article
This paper is concerned with the parameter identification of an unmanned surface vehicle (USV) with fully unknown coefficients. An online adaptive parameter identification method is proposed for the USV to identify its model parameters without the condition of persistence of excitation. Specifically, a composite adaptive update law is developed bas...
Article
Full-text available
This paper considers the leader–follower synchronization control of under-actuated marine vessels for underway replenishment. An integrated guidance and control method is presented to achieve the underway replenishment operations despite of unknown model uncertainties, external disturbances, and unknown velocities of the leader vessel. Specifically...
Article
This paper is concerned with problems of stability of discrete-time systems with infinite delays. Several new theorems for stability analysis of the concerned delayed systems are developed. Specifically, uniform stability, uniform asymptotic stability, global uniform asymptotic stability, exponential stability and global exponential stability are i...
Article
This paper presents a distributed optimization method for coordinated dynamic positioning (CDP) of multiple unmanned surface vessels (USVs) subject to uncertainties and disturbances. The control objective is to achieve a relative dynamic positioning of multiple USVs with the optimal position encoded in a sum of local functions. Two types of distrib...
Article
This article investigates the distributed optimal output consensus problem of second‐order uncertain nonlinear multiagent systems over weight‐unbalanced directed networks. Under the standard assumption that local cost functions are strongly convex with globally Lipschitz gradients, a novel distributed dynamic state feedback controller is developed...
Article
This paper proposes a novel general framework with new Lyapunov stability theorems for control problems of systems with unbounded delays. Under this framework, the delayed input can be captured in the stability estimate by augmenting it as a state with initial conditions. Then by applying the novel framework, we consider the stabilization problems...
Article
This paper addresses motion planning problem of multiple autonomous surface vehicles (ASVs) for formation reconfiguration subject to static obstacles. The motion planning problem include two objectives. The first objective is to generate feasible control signals toward a goal region considering the vehicle kinematics. The second objective is to avo...
Article
Distributed coordination of multi-agent systems (MASs) has received considerable attention and advanced rapidly in the past years. This paper reviews the recent results on cooperative control of MASs, and in particular cooperative control under various agent dynamics, under communication transmission delays, and under event-triggered strategies. In...
Article
This paper is concerned with a self-triggered three-dimensional coordinated path following problem for a fleet of under-actuated disk-type autonomous underwater gliders (AUGs) subject to input constraints as well as internal model uncertainties and external ocean disturbances. A modular backstepping design approach is employed to devise three-dimen...
Article
This paper investigates the global cooperative output regulation problem of continuous-time linear multi-agent systems (MASs), under the communication constraint of limited bandwidth. With a novel scaling function strategy, a distributed protocol based on the sampled and quantized data is designed to solve this problem. Compared with the existing w...
Preprint
Full-text available
This paper investigates the distributed optimal output consensus problem of heterogeneous linear multi-agent systems over weight-unbalanced directed networks. A novel distributed continuous-time state feedback controller is proposed to steer the outputs of all the agents to converge to the optimal solution of the global cost function. Under the sta...
Preprint
Full-text available
In this note, a novel observer-based output feedback control approach is proposed to address the distributed optimal output consensus problem of uncertain nonlinear multi-agent systems in the normal form over unbalanced directed graphs. The main challenges of the concerned problem lie in unbalanced directed graphs and nonlinearities of multi-agent...
Article
This article investigates the leader-following consensus problem of heterogeneous linear multiagent systems under switching and directed topologies. It is assumed that the communication between agents suffers from time-varying delays and only the neighboring agents of the leader are able to get access to the information of the leader agent, includi...
Article
In this paper, distributed formation tracking control with collision avoidance is addressed for a group of under-actuated unmanned surface vehicles subject to physical constraints and dynamical uncertainties. An extended-state-observer-based distributed model predictive control method is proposed for achieving a safe formation. Specifically, the ve...
Article
This paper is concerned with the disturbance estimation and velocity recovery of autonomous surface vehicles subject to unknown input gains, in addition to lumped uncertainties composed of unknown internal dynamics and external disturbances. Existing extended state observer design methods are not applicable due to the fact that some prior knowledge...
Article
In this paper, we address the distributed average tracking (DAT) problem for linear multi-agent systems with heterogeneous dynamics and external disturbances. The objective is that each agent can accurately track the desired tracking signal by designing controllers without initialization. The desired tracking signal means the average of individual...
Article
This article considers the control problem of linear strict‐feedback systems with an infinite‐delayed integrator. The integrator backstepping design approach is used to construct a predictor feedback controller. By applying the stability theorem developed in our previous work for systems with unbounded delays, exponential stability of the resulting...
Article
In this paper, we consider a finite-time output regulation problem for a class of nonlinear multi-agent systems with unity relative degree. First, the robust estimation for the system matrix of the exosystem is achieved via a distributed observer, provided that the estimation error converges to zero within a finite time. Second, another observer is...
Article
This article is concerned with the memory fault detection filtering design in finite frequency domain for discrete‐time systems with polytopic uncertainties. Under the assumption that both disturbances and faults are restricted to finite frequency ranges, that is, the low, middle, or high frequency range, an admissible memory fault detection filter...
Article
This paper studies the moving-target enclosing control problem for a group of mobile agents, under the assumption that the amplitude of the target's velocity is unknown a priori. The target's velocity is time-varying and can be viewed as a signal generated by an exogenous linear system. The neighbor topology of the agents is determined by their pos...
Article
This paper studies the robust cooperative output regulation problem of heterogeneous uncertain linear multi-agent systems under unbounded distributed transmission delays. A novel distributed observer is first proposed to estimate the state of an exosystem in the presence of unbounded distributed transmission delays. Then two novel distributed contr...
Article
In this article, the output containment control problem of heterogeneous linear multiagent systems (MASs) with unbounded distributed transmission delays is considered. A key technical lemma is first established to show that the distributed observers under unbounded distributed transmission delays can be utilized to estimate the convex combination o...
Article
This article investigates the event-triggered output consensus problem for a class of unknown heterogeneous discrete-time linear multiagent systems in the presence of unmodeled dynamics. The agents have individual nominal dynamics with unknown parameters, and the unmodeled dynamics are in the form of multiplicative perturbations. A novel design fra...
Article
In this article, we address the synchronization problem of networked uncertain Euler-Lagrange systems subject to disturbances, network delays, and uniformly connected switching networks. Compared with existing works, the current problem setting is more practical and technically more challenging. First, to tackle the disturbances under switching net...
Article
This article investigates the leader-following output consensus problem of heterogeneous linear multiagent systems, where the nonidentical followers are subject to norm bounded parameter uncertainties. Two novel distributed event-triggered consensus strategies based on state feedback and output feedback, respectively, are proposed to solve the lead...
Article
In this article, an output regulation problem is considered for nonlinear multiagent systems with unity relative degree, in which nodes are coupled by dynamic edges. The inputs of the edge dynamic systems are determined by the error outputs of the node dynamic systems. Similarly, the neighboring inputs of the node dynamic systems are formed by the...
Article
Cooperative output regulation (COR) of multiagent systems having heterogeneous uncertain nonlinear dynamics is often challenging because of the complex system dynamics and the coupling among agents. This article develops an adaptive internal model-based distributed regulator such that the outputs of a network of nonlinear agents are all regulated t...
Article
The consensus problem of heterogeneous linear multi-agent systems (MASs) with communication, input and output time-delays is studied in this paper. An observer-predictor is designed to estimate the future states of each agent, and then a distributed dynamic controller based on this observer-predictor is proposed to solve the concerned problem. Swit...
Article
The coverage control problem for a network of heterogeneous mobile sensors with bound position measurement errors on a circle is addressed in this paper. A practical measurement error model is considered in which only the upper bounds of the measurement errors are known by the sensors a priori. The coverage cost function is defined as the largest a...
Article
This article investigates the robust output regulation problem of a class of minimum‐phase linear uncertain systems subject to limited measurement information. A novel dynamic quantized output feedback control law together with a hybrid quantized feedback control policy is developed. By means of Lyapunov analysis, it is shown that the tracking erro...
Article
The consensus problem of heterogeneous second-order nonlinear uncertain multi-agent systems under switching networks is addressed by a distributed control approach. The network communication of all systems is subject to arbitrarily bounded and nonuniform time-varying delays. Based on the internal model principle, a nonlinear distributed dynamic con...
Article
The problem of localization and enclosing control of an unknown moving target by networked mobile agents in a plane is considered in this paper. Each agent is supposed to be able to only measure the bearing angle to the target. Based on the bearing measurements of each agent and its neighbors, an estimator is proposed for each agent to localize the...
Article
This paper addresses Lipschitz conditions of infinite dimensional systems. Three types of Lipschitz conditions are discussed, namely, the compact set Lipschitz condition, the local Lipschitz condition and the bounded set Lipschitz condition. These three conditions are equivalent in finite dimensional systems but not necessarily equivalent in infini...
Article
This paper investigates the cooperative output regulation problem for heterogeneous linear multi-agent systems by event-triggered control, where the system matrix of the exosystem is not available to all agents. First, an event-triggered adaptive distributed observer is designed for each agent to estimate both the state and the system matrix of the...
Article
This article addresses the event-triggered adaptive fuzzy output-feedback control problem for a class of nonstrict-feedback nonlinear systems with asymmetric and time-varying output constraints, as well as unknown nonlinear functions. By designing a linear observer to estimate the unmeasurable states, a novel event-triggered adaptive fuzzy output-f...
Article
This work addresses the finite‐time optimal control problem for a class of interconnected nonlinear systems with powers of positive odd rational numbers. A series of homogeneous controllers, which are capable of guaranteeing the local finite‐time stability of the closed‐loop systems, are first developed using the adding one power integrator method...
Article
This article addresses the cooperative output tracking problem of a class of linear minimum-phase multiagent systems, where the agent dynamics are unknown and heterogeneous. A distributed event-triggered model reference adaptive control strategy is developed. It is shown that under the proposed event-triggered control strategy, the outputs of all t...
Article
This paper devotes to investigating the issue of fuzzy adaptive control for a class of strict-feedback nonlinear systems with non-affine nonlinear faults. The computational complexity is reduced by adopting the dynamic surface control technique. Under the framework of finite-time stability, a novel faulttolerant control strategy is designed so that...
Article
This paper investigates the leader-following synchronization problem of uncertain Euler-Lagrange multi-agent systems subject to communication delays, disturbances and uniformly connected switching networks. The current settings cause great challenges to the solvability of the problem. To tackle these technical challenges, we make an extension to Ba...
Article
This paper addresses the stability and stabilization of infinite delay systems, which are more general but also more challenging to deal with than bounded delay systems. Based on a general model of infinite delay systems and a newly approved key technical lemma, several new Lyapunov theorems for uniform asymptotical stability and exponential stabil...
Article
In this paper, we study the distributed containment control problem with multiple leaders for nonlinear multi-agent systems (MASs) with unstabilizable linearizations under the directed topology. A novel distributed control design approach is developed to simultaneously deal with the unstabilizable linearizations and nonlinear interactions among age...
Article
In this article, the event-triggered and self-triggered leader-following output-feedback control problems are investigated for a class of high-order stochastic nonlinear multiagent systems (MASs) under an undirected graph. First, using the high-gain method, the observer is designed to estimate the unmeasured state variables of the given nonlinear s...
Article
This paper addresses the semi-global stabilization problem of linear systems with simultaneous presence of distributed infinite input delays and actuator saturations. Two low gain controllers are proposed, respectively, for two classes of linear systems with both infinite input delays and actuator saturations. It is shown that under our first contr...
Article
This article studies the robust output regulation problem (RORP) for a class of uncertain linear systems with unknown exosystems via event-triggered control (ETC). Compared with existing related works, the system matrix of the exosystem under consideration is allowed to contain unknown parameters. Based on an adaptive internal model, an ETC strateg...
Article
This paper addresses the finite-time adaptive fuzzy control problem for a class of nonstrict-feedback uncertain nonlinear systems via an event-triggered strategy. A novel design scheme, consisting of finite-time adaptive fuzzy controller and event-triggering mechanism (ETM), is proposed to decrease the number of data transmission and the number of...
Article
This paper addresses the adaptive trajectory tracking problem of uncertain Euler–Lagrange systems subject to external disturbances. In comparison with existing literature, our work has its distinctive characteristics. First, a large class of persistent external disturbances with unbounded energy can be accommodated, which can be a combination of fi...
Article
The leader-following attitude consensus problem of networked rigid spacecraft systems is addressed by a distributed control law. Compared with existing results, the salient characteristics of this work is that the communication network is allowed to be directed and switching. In particular, the switching network only needs to be jointly connected,...
Article
This paper considers the consensus problem of linear multi-agent systems with distributed infinite transmission delays. A novel low gain controller is proposed and it is shown that the proposed controller can solve the consensus problem if the open loop agent dynamics have no exponentially unstable eigenvalues and the communication topology is fixe...
Article
This paper investigates the cooperative output regulation problem for heterogeneous linear multiagent systems under fixed communication graphs via event-triggered control. A fully distributed event-triggered dynamic output feedback control law is proposed based on the feedforward design approach. At the same time, a fully distributed dynamic event-...
Article
In this paper, we consider the leader-following consensus problem of uncertain Euler-Lagrange multi-agent systems. In comparison with existing results, the leader system is used to formulate both the reference trajectory and external disturbances, and the dynamics of the leader system contains unknown parameters. The current setting makes our probl...
Article
In this study, we investigate the leader-following consensus problem of a class of heterogeneous secondorder nonlinear multi-agent systems subject to disturbances. In particular, the nonlinear systems contain uncertainties that can be linearly parameterized. We propose a class of novel distributed control laws, which depends on the relative state o...
Article
This paper considers a robust adaptive fuzzy control problem for a class of uncertain nonlinear systems via an eventtriggered control strategy. Fuzzy logic systems (FLSs) are used to approximate the unknown nonlinear functions in the nonlinear system. A novel robust adaptive control scheme together with a novel event-triggering mechanism (ETM) is p...
Article
This paper investigates the consensus problem of linear multi-agent systems subject to external disturbances via distributed event-triggered adaptive control. First, a distributed event-triggered adaptive output feedback control strategy is proposed for each agent. It is shown that under this control strategy, the consensus problem can be solved fo...
Article
This paper investigates the consensus problem of single integrator multi-agent systems with unbounded time-varying transmission delays and fixed directed topology. A distributed controller is proposed taking into consideration the unbounded transmission delays. It is shown that the consensus problem can be solved via the proposed controller under t...
Article
In this paper, we investigate the distributed output-feedback tracking problem of nonlinear multiagent systems (MASs) where nonlinear functions of agent dynamics depend on unmeasurable states. Most existing results on output-feedback control of nonlinear MASs are concerned with nonlinear agent dynamics in output canonical form in which the nonlinea...
Article
This paper investigates the adaptive output regulation problem for heterogeneous linear multiagent systems under randomly switching communication topologies. The switching mechanism is governed by a time-homogeneous Markov process, whose states correspond to all possible communication topologies among agents. A novel distributed adaptive cooperativ...
Article
This paper studies the cooperative control problem of multiple nonlinear benchmark systems perturbed by second-order moment processes. The nonlinear benchmark system consists of a moving car and a rolling ball in oscillating surroundings. When the leader is only accessible to a small part of the followers in a directed graph, a new vectorial backst...
Article
This paper investigates the output consensus problem for heterogeneous linear multi-agent systems via event-triggered control. By introducing a dynamic compensator for each agent, a fully distributed event-triggered control strategy with an adaptive event-triggering mechanism is proposed. It is shown that under the proposed control strategy, all ag...
Article
The circle formation problem for a group of mobile agents with limited interaction range is addressed in this paper. Distributed switching control laws are developed for multi-agent systems to form prescribed formations from any initial configurations on a circle. It is shown that the desired circle formation can be achieved if a parameter dependin...
Article
This note presents a static distributed formation control law for nonholonomic vehicles subject to velocity constraints, such that the controlled vehicles travel along a common circle with the given center and radius, while maintaining a desired spaced formation. The center is assumed to be known to only some vehicles. The proposed controller does...
Article
In this paper, we study the output consensus problem of networked heterogeneous nonlinear systems. In contrast to existing results on similar problems, output consensus of all systems is achieved with some robustness not only to heterogeneous dynamics with uncertainties but also to unreliable network communication in terms of network connectivity a...
Article
This paper investigates the stabilization problem of linear systems with distributed infinite input delays. By introducing a stability result on systems with infinite delays, it is shown that a stabilizable linear system with distributed infinite input delays can be globally asymptotically stabilized with low gain controllers as long as the open-lo...
Article
Full-text available
This paper addresses the cooperative output regulation problem of linear multi-agent systems under switching communication topologies. A distributed event-triggered control scheme is proposed so that the cooperative output regulation problem is solved with only intermittent communication. The communication topology is not required to be connected a...
Article
A new adaptive distributed controller is developed for the leader‐following consensus problem of multiple uncertain Euler‐Lagrange systems. A distinct feature of our proposed approach as opposed to the existing ones is that it does not need the exchange of controller's state among the communication network. As a consequence, it not only makes the i...