Zhiyong Chen

• University of Newcastle Australia

With advances in network control systems, new applications such as the analysis of opinion dynamics have emerged. Using mathematical tools, various dynamic models have been developed to study how people change opinions in social settings. One such model is the DeGroot-Friedkin model, a two-stage approach for sequential discussion of multiple issues...

Constraints on system states are essential performance requirements in various control systems. This paper delves into the problem of cooperative fault-tolerant control under state constraints for a specific class of nonlinear multiple-agent systems. To achieve asymptotic estimation of states and faults, we propose a distributed state-fault observe...

Autonomous synchronization presents a novel paradigm that circumvents the need for prior knowledge of target agent dynamics in the conventional synchronization of heterogeneous multi-agent systems (MASs). It employs a dynamics update law and a state synchronizing control law, collectively termed a two-level controller, to facilitate synchronization...

p>Actor-critic (AC) algorithms are model-free deep reinforcement learning techniques that have consistently demon- strated their effectiveness across various domains, especially in addressing continuous control challenges. Enhancing exploration (action entropy) and exploitation (expected return) through more efficient sample utilization is pivotal...

p>Actor-critic (AC) algorithms are model-free deep reinforcement learning techniques that have consistently demon- strated their effectiveness across various domains, especially in addressing continuous control challenges. Enhancing exploration (action entropy) and exploitation (expected return) through more efficient sample utilization is pivotal...

Empirical studies suggest a deep intertwining between opinion formation and decision-making processes, but these have been treated as separate problems in the study of dynamical models for social networks. In this paper, we bridge the gap in the literature by proposing a novel coevolutionary model, in which each individual selects an action from a...

Actor-critic(AC) algorithms are known for their efficacy and high performance in solving reinforcement learning problems, but they also suffer from low sampling efficiency. An AC based policy optimization process is iterative and needs to access the agent-environment to evaluate and update the policy by rolling out the policy, collecting rewards an...

The existing cryptosystem based approaches for privacy-preserving consensus of networked systems are usually limited to those with undirected topologies. This paper proposes a new privacy-preserving algorithm for networked systems with directed topologies to reach confidential consensus. As a prerequisite for applying the algorithm, a structural co...

An emerging actuation technique in piezo driven nanopositioners is differential actuation, where each axis has two opposing actuators that operate differentially and provide bilateral motion. It has simultaneous benefits of improving linearity and range of displacement. However, few methods for displacement sensing employing in-situ transducers hav...

Actor-critic (AC) algorithms are a class of model-free deep reinforcement learning algorithms, which have proven their efficacy in diverse domains, especially in solving continuous control problems. Improvement of exploration (action entropy) and exploitation (expected return) using more efficient samples is a critical issue in AC algorithms. A bas...

This paper aims to create a secure environment for state estimation and control design of a networked system composed of multiple dynamic entities and remote computational units, in the presence of disclosure attacks. In particular, both dynamic entities and computational units may be vulnerable to attacks and become malicious. The objective is to...

In this article, we investigate a moving-target-fencing problem for multiple vehicles using nearest neighbor rules where the target moves with an unknown constant velocity. Without a predefined stand-off distance or formation, two local cooperative controllers are proposed using only the relative position information from the target and its neighbo...

Soft actor-critic (SAC) is an off-policy actor-critic (AC) reinforcement learning (RL) algorithm, essentially based on entropy regularization. SAC trains a policy by maximizing the trade-off between expected return and entropy (randomness in the policy). It has achieved the state-of-the-art performance on a range of continuous control benchmark tas...

This paper addresses the resilient consensus problem in the presence of faulty nodes whose state updating is randomly unreliable. Unlike the existing approaches using elimination of extreme neighbor nodes with state updating or trustworthiness evaluation of neighbor nodes by historical information, this paper presents a novel multi-armed bandit bas...

The existing cryptosystem based approaches for privacy-preserving consensus of networked systems are usually limited to those with undirected topologies. This paper proposes a new privacy-preserving algorithm for networked systems with directed topologies to reach confidential consensus. As a prerequisite for applying the algorithm, a structural co...

This paper investigates the nonuniform and nonconvex input constrained flocking control problem of continuous-time multi-agent systems. A distributed flocking control algorithm is proposed for each agent using the local information from its neighbor agents subject to nonuniform and nonconvex control constraints. Based on a constraint scaling factor...

This paper revisits a well studied leader-following consensus problem of linear multi-agent systems, while aiming at follower nodes' transient performance. Conventionally, when not all follower nodes have access to the leader's state information, distributed observers are designed to estimate the leader's state, and the observers are coupled via co...

Soft Actor-Critic (SAC) is an off-policy actor-critic reinforcement learning algorithm, essentially based on entropy regularization. SAC trains a policy by maximizing the trade-off between expected return and entropy (randomness in the policy). It has achieved state-of-the-art performance on a range of continuous-control benchmark tasks, outperform...

Actor-critic (AC) algorithms are known for their efficacy and high performance in solving reinforcement learning problems, but they also suffer from low sampling efficiency. An AC based policy optimization process is iterative and needs to frequently access the agent-environment system to evaluate and update the policy by rolling out the policy, co...

The paper proposes a novel event-triggered control scheme for nonlinear systems. Specifically, the closed-loop system is associated with a pair of auxiliary input and output. The auxiliary output is defined as the derivative of the continuous-time input function, while the auxiliary input is defined as the input disturbance caused by the sampling o...

We study a novel piezo-driven nanopositioning mechanism in the horizontal plane. For each horizontal axis, we employ two externally leverage mechanisms with flexure hinges to provide bilateral displacement of the output stage as well as amplified displacement with respect to strokes of two piezo stack actuator. The bilateral amplified motion is ach...

This article studies the moving‐target‐fencing problem of multiple second‐order vehicles, where the target moves with an unknown constant velocity. Without a predefined stand‐off distance or formation, two classes of local cooperative controllers are proposed with and without velocity measurements. Specifically, the first controller uses the relati...

Economic dispatch is a critical problem in operation of power grids. A consensus-based algorithm was recently proposed to solve the economic dispatch problem in a distributed manner. In this paper, we propose a novel secure scheme for the consensus-based economic dispatch algorithm using the Paillier cryptosystem. This secure scheme ensures that no...

This paper revisits a well studied leader-following consensus problem of linear multi-agent systems, while aiming at follower nodes’ transient performance. Conventionally, when not all follower nodes have access to the leader’s state information, distributed observers are designed to estimate the leader’s state, and the observers are coupled via co...

This paper aims at secure and privacy-preserving consensus algorithms of networked systems. Due to the technical challenges behind decentralized design of such algorithms, the existing results are mainly restricted to a network of systems with simplest first-order dynamics. Like many other control problems, breakthrough of the gap between first-ord...

This paper formulates a new type of synchronization problem for heterogeneous multi-agent systems (MASs), called autonomous synchronization. In this problem, neither the synchronized agent dynamics nor the synchronized states are specified a priori, instead, they are autonomously determined by the inherent properties and the initial states of agent...

In traditional adaptive control, the certainty equivalence principle suggests a two‐step design scheme. A controller is first designed for the ideal situation assuming the uncertain parameter was known, and it renders a Lyapunov function. Then, the uncertain parameter in the controller is replaced by its estimation that is updated by an adaptive la...

For a linear time varying (LTV) system containing stable and unstable modes, the paper gives the necessary and sufficient conditions for asymptotic decoupling of stable modes. Establishment of the conditions relies on newly developed techniques for analyzing matrix exponential and state transition matrix. The research exploits fundamental propertie...

Guided policy search algorithms have been proven to work with incredible accuracy for not only controlling a complicated dynamical system, but also learning optimal policies from various unseen instances. One assumes true nature of the states in almost all of the well known policy search and learning algorithms. This paper deals with a trajectory o...

Trajectory optimization is a fundamental stochastic optimal control problem. This paper deals with a trajectory optimization approach for unknown complicated systems subjected to stochastic sensor noise. The proposed methodology assimilates the benefits of conventional optimal control procedure with the advantages of maximum likelihood approaches t...

This paper proposes an encrypted observer-based control paradigm for enhancement of cybersecurity in networked control systems. The proposed paradigm exploits a semi-homomorphic encryption technique which enables the required computation to be done over encrypted data without any need for decryption at controller and observer levels. This improves...

We address design, implementation, and characterization of semiconductor strain gauges as stage displacement sensors with small footprint for piezo-driven nanopositioners in differential actuation mode. The strain gauges are not collocated with the stage of the nanopositioner. They are attached to piezo stack actuators in both longitudinal and tran...

This paper studies robust output synchronization of heterogeneous linear MIMO multi-agent systems (MAS) via output communication/feedback. The problem can be technically converted into two coupled problems, namely a well solved perturbed consensus problem and perturbed regulation of each individual agent. The latter motivates the so-called γ-stabil...

Management of resources is a constant topic in industrial systems. How to use minimum communication resources is of particular interest for control and estimation of networked systems. It raises the question for researchers in the field: how often should one update control and estimation? One of the most intelligent approaches is to trigger updates...

This paper proposes an active levitation control system composed of an active magnetic bearing (AMB) rotor and an interval type-2 (IT2) model-based fuzzy logic controller (FLC). The controller aims to achieve fast and stable levitation by compensating for system uncertainties via proper design of IT2 membership functions. In particular, the complex...

This paper addresses the distributed consensus problem in the presence of faulty nodes. A novel weight learning algorithm is introduced such that neither network connectivity nor a sequence of history records is required to achieve resilient consensus. The critical idea is to dynamically update the interaction weights among neighbors learnt from th...

This paper aims to create a secure environment for networked control systems composed of multiple dynamic entities and computational control units via networking, in the presence of disclosure attacks. In particular, we consider the situation where some dynamic entities or control units are vulnerable to attacks and can become malicious. Our object...

In this paper, we make a bridge between two theories in social psychology, namely social judgment theory and balance theory, exploiting nonlinear models. In particular, we propose a model of opinion dynamics which takes into account the notions of latitude of acceptance, latitude of noncommitment, and latitude of rejection from social judgment theo...

The existence of hysteresis phenomenon in piezoelectric actuators of nanopositioners adversely affects their performance, e.g. image distortion in Atomic Force Microscopy. A usual approach to circumnavigate hysteresis nonlinearity is feedforward compensation where the performance depends extensively on the accuracy of the hysteresis model. To achie...

A systematic stabilization approach is provided for systems whose regulation error dynamics is subject to rational nonlinearities given prior knowledge of the system zero-error steady-state condition and a proper internal model. The error dynamics is cast in a differential-algebraic form so as to address the synthesis of controller parameters by a...

The existing economic dispatch (ED) control structures in power systems are based on solving a quadratic optimisation problem, which can only guarantee the optimal steady‐state performance. In this study, the authors formulate the real‐time ED problem for the transient operation of power systems as a dynamic model predictive control (MPC) optimisat...

A class of event-triggered stabilization technique works with a small gain theorem when the controlled system has a certain input-to-state stability (ISS) property from the measurement (sensor) disturbance to state. However, such an ISS property is not always achievable for nonlinear systems. In particular, early research suggests that global inter...

This paper addresses the output synchronization problem for heterogeneous nonlinear multi-agent systems with distributed event-based controllers. Employing the two-step synchronization process, we first outline the distributed event-triggered consensus controllers for linear reference models under a directed communication topology. It is further sh...

A multi-unmanned surface vessel (USV) formation control system is established on a novel platform composed of three 1.2-m-long hydraulic jet propulsion surface vessels, a differential GPS reference station, and inter-vessel Zigbee communication modules. The system is also equipped with an upper level collective multi-USV protocol and a lower level...

In this letter, we propose a novel model of opinion dynamics which takes into account the notions of latitude of acceptance, latitude of noncommitment, and latitude of rejection from social judgment theory. We examine the asymptotic behavior of the proposed model. Moreover, introduction of latitude of rejection and as a result negative interactions...

This paper deals with the characterization of piezoelectric ceramic type sensors integrated in a compact high-speed 2-DOF nano-positioner to measure large signal stage displacement. Such transducers are very attractive because they provide measurements in a wide frequency bandwidth with low noise, they do not require bulky electronic modules and ar...

Output synchronization of nonlinear heterogeneous networked systems has been well investigated within a two-step framework. A reference model is designed for each agent and they achieve consensus through a proper collaborative control strategy. Then, a local regulation controller is constructed to drive each agent’s output to the desired trajectory...

A multi-unmanned surface vessel (USV) formation control system is established on a novel platform composed of three 1.2 meter-long hydraulic jet propulsion surface vessels, a differential GPS reference station, and inter-vessel Zigbee communication modules. The system is also equipped with an upper level collective multi-USV protocol and a lower le...

Directed acyclic graphs (DAGs) widely exist in natural biological, industrial, and social networked systems. This brief explores the effects of adding a reverse edge, across a so-called stem, in a DAG on consensus performance. In particular, it quantitatively reveals the effects in terms of the in-degrees of the surpassed stem nodes. The study furt...

This paper explores regulation theory for the design of robust precision attitude tracking of an uncertain rigid spacecraft with external disturbances. Focusing on the attitude system in terms of unit quaternions with an unknown inertia matrix and unmodeled input disturbances, we first introduce specific nonlinear logic such that the resultant erro...

A class of cooperative controllers is designed for a group of autonomous vehicles, using the relative positions between geographical neighbors and a specified target. The controller is equipped with three components: attractive component that drives each vehicle towards the target, repulsive component between adjacent vehicles, and rotation compone...

In traditional adaptive control, the certainty equivalence principle suggests a two-step design scheme. A controller is first designed for the ideal situation assuming the uncertain parameter was known and it renders a Lyapunov function. Then, the uncertain parameter in the controller is replaced by its estimation that is updated by an adaptive law...

This paper studies the distributed adaptive consensus problem for multi-agent systems (MASs) subject to nonlinearly parameterized uncertainties. In the existing research, an adaptive consensus scheme was developed for the same scenario but under the assumption that the uncertainties must be linearly parameterized in their unknown parameters. In thi...

Nussbaum functions have been successfully used in adaptive controller design for dealing with unknown control direction since the original work in 1983. However, for time-varying control coefficients of an unknown sign (positive or negative), only a special Nussbaum function can be proved to be effective based on the explicit calculation on the par...

In this paper, the output synchronization problem for nonlinear heterogeneous multi-agent systems is studied in a switching network of time-varying directed graphs. The scenario under consideration is complicated in the sense that none of the graphs is assumed to be connected (containing a spanning tree). Within a two-step framework for output sync...

Input-to-state stability (ISS) for a switched system is a stronger property than stability in characterizing the external influence on system performance. In this paper, we study ISS for a linear switched system with marginally stable subsystems and hence with polynomially unstable subsystems. Moreover, we aim to calculate an explicit ISS gain whic...

In this paper, we study the cooperative output regulation problem for heterogeneous linear discrete-time time-delay multi-agent systems by adaptive distributed observers. An adaptive distributed observer-based approach was recently proposed for estimating both a leader's state and its system dynamics, to each follower. This approach is applied to d...

Hysteresis modeling is interesting yet challenging for piezoelectric actuated systems, which are often used in micro/nano scale measurement and manufacturing equipments. However, due to its complexity, few efforts have been devoted to characterizing cross-coupling hysteresis effect of multi-axis piezoelectric micropositioning stages. To this end, a...

The two volume set LNAI 10984 and LNAI 10985 constitutes the refereed proceedings of the 11th International Conference on Intelligent Robotics and Applications, ICIRA 2018, held in Newcastle, NSW, Australia, in August 2018. The 81 papers presented in the two volumes were carefully reviewed and selected from 129 submissions. The papers in the first...

The two volume set LNAI 10984 and LNAI 10985 constitutes the refereed proceedings of the 11th International Conference on Intelligent Robotics and Applications, ICIRA 2018, held in Newcastle, NSW, Australia, in August 2018. The 81 papers presented in the two volumes were carefully reviewed and selected from 129 submissions. The papers in the first...

Milling chatters caused by the regenerative effect is one of the major limitations in increasing the machining efficiency and accuracy of milling operations. This paper studies robust active chatter control for milling processes with variable pitch cutters whose dynamics are governed by multidelay nonlinear differential equations. We propose a stat...

This paper explores a cooperative practical output regulation problem for a class of heterogeneous multiagent nonlinear systems by event-based output feedback. Specifically, we shall restrict our attention to the situation of sampled-data-based local measurements. As usual, due to agents heterogeneity, we first convert the problem into a stabilizat...

This paper focuses on constructing genotypic predictors for antiretroviral drug susceptibility of HIV. To this end, a method to recover the largest elements of an unknown vector in a least squares problem is developed. The proposed method introduces two novel ideas. The first idea is a novel forward stepwise selection procedure based on the magnitu...

This paper studies a stabilization problem for linear MIMO systems subject to external perturbation that further requires the closed-loop system render a specified gain from the external perturbation to the output. The problem arises from control of networked systems, in particular, robust output synchronization of heterogeneous linear MIMO multi-a...

The paper proposes a novel event-triggered control scheme for nonlinear systems based on the input-delay method. Specifically, the closed-loop system is associated with a pair of auxiliary input and output. The auxiliary output is defined as the derivative of the continuous-time input function, while the auxiliary input is defined as the input dist...

Secure and privacy preserving consensus algorithms have shown their great importance in many areas. Due to the technical challenges behind decentralized design of such algorithms, the existing results are mainly restricted to a network of nodes with simplest first-order dynamics. In this paper, we explore a Paillier encryption based average consens...

This paper examines the structural controllability for a group of agents, called followers , connected to each other based on the consensus law under commands of multiple leaders , which are agents with superior capabilities, over a fixed communication topology. It is proved that the graph-theoretic sufficient and necessary condition for the se...

This paper examines the structural controllability for a group of agents, called followers, connected to each other based on the consensus law under commands of multiple leaders, which are agents with superior capabilities, over a fixed communication topology. It is proved that the graph-theoretic sufficient and necessary condition for the set of f...

Solvability of a consensus problem for multi-agent systems in switching networks heavily relies on stabilization techniques for switched systems. The consensus problem becomes challenging when the agent dynamics are complicated that require stability of a switched system composed of unstable subsystems. Moreover, complicated dynamics bring other co...

This note develops a discrete-time predictor feedback control scheme for continuous-time multi-agent systems with input and communication time-delays. With measurement of locally available relative state signals among neighbored agents, the controller is able to achieve consensus for a large variety of linear open-loop agent dynamics, including exp...

Robust output regulation is a controller design theory for achieving reference tracking and disturbance rejection as well as system stability. The main feature of the theory is that the reference and/or disturbance signals have explicit structural description, especially by an exosystem. By decoding this structural information, the desired steady s...

Robust stabilization of nonlinear systems has been extensively studied subject to both static and dynamic uncertainties. In particular, a class of nonlinear controllers can be explicitly constructed based on recursively applying the small gain theorem. In this paper, we further investigate the so-called robust input-to-output stabilization problem...

This technical note considers global robust output regulation (GROR) for nonlinear lower triangular systems with uncertain exosystems. Under standard minimum phase and solvability of regulator equations like assumptions, the problem has not been completely solved to some extend in the past literature. It has attracted many researchers to contribute...

This paper investigates a group of multiagents moving on a 2-D plane with a constant speed but maneuverable headings. It is called a minimal control multiagent model (MCMA) when each agent employs a static decentralized control law that relies on its neighbors’ relative positions with respect to its local reference frame. In other words, the contro...

The output synchronization of heterogeneous multi-agent systems becomes more challenging when only output information is exchanged over the network rather than state information. We showed that the problem can be solved in two mutually coupled steps, namely perturbed consensus which is closely related to the well solved synchronization of homogeneo...

The authors consider a global robust asymptotic stabilization problem (GRS) for cascaded systems having dynamic uncertainties that are not necessarily input-to-state stable (ISS). Specifically, a recursive Lyapunov design approach is developed by induction on the system relative degree, providing a smoothly globally stabilizing controller. It is ap...

Consensus of a network with a directed acyclic graph, a directed graph with no directed cycles, is always guaranteed if it contains a spanning tree. The note studies the effect of adding edges to a directed acyclic graph that may result in a directed cycle. It is shown that the effect on consensus performance of the whole network is only determined...

Precise control of a pneumatic muscle actuator is a challenging problem, due to its nonlinear and time-varying characteristics. Specifically, it can be modeled as parallel connection of a nonlinear friction force, a nonlinear spring, and a nonlinear contractile element. It is difficult to identify the coefficients associated with these elements wit...

Fueled by applications in sensor networks, these years have witnessed a surge of interest in distributed estimation and filtering. A new approach is hereby proposed for the Distributed Kalman Filter (DKF) by integrating a local covariance computation scheme. Compared to existing well-established DKF methods, the virtue of the present approach lies...

Due to its superb flexibility, efficiency, and tractility, flexible electronic production is widely used in the manufacturing of thin-film solar cells, microscale sensors, high-resolution dis-players, illumination equipments, and integrated artificial tissues. Electrospinning is an essential procedure in flexible electronic production, where a micr...