Chao Zhai

China University of Geosciences · School of Automation

A novel individual-based alignment/repulsion algorithm is proposed in this note for a flock of multiple agents. With this algorithm, each individual repels its sufficiently close neighbors and aligns to the average velocity of its neighbors with moderate distances. In both mathematical analysis and numerical simulation, we prove that the algorithm...

This paper proposes a sweep coverage formulation for a multi-agent system to cover a region with uncertain workload density, and provides a decentralized coverage algorithm based on the formulation. To achieve the coverage, the covered region is divided into a finite number of stripes, and an algorithm is proposed by incorporating two operations on...

The mirror game has been recently proposed as a simple, yet powerful paradigm for studying interpersonal interactions. It has been suggested that a virtual partner able to play the game with human subjects can be an effective tool to affect the underlying neural processes needed to establish the necessary connections between the players, and also t...

The significant penetration of renewable energy resources into power systems introduces intermittent disturbances that drive the system away from its stable operating point (i.e., equilibrium). Nevertheless, as long as the system states are still contained inside a region of attraction (ROA), the system will finally return to the normal operating e...

It has long been a challenging task for multi-agent systems (MASs) to inexpensively service probable events in non-convex environments. Coverage control provides an efficient framework to address MAS deployment problem for optimizing the cost of tackling unknown events. By means of the divide-and-conquer methodology, this paper proposes a sectorial...

To address significant disturbances and unavoidable measurement noises during aeroengine transient tests in the Intake Environmental Pressure Simulation System (IEPSS), a sliding mode active disturbance rejection controller (SMADRC) is designed. Meanwhile, a particle swarm optimization (PSO) algorithm is adopted for optimizing and tuning the parame...

Large-scale blackouts normally go through several sequential phases according to the propagation speed of branch outages and the disruption level of power grids. It is crucial to eliminate the propagation of cascading outages in its infancy. In this chapter, a model predictive approach is proposed to protect power grids against cascading blackouts....

The responsive and effective protective actions are vital to the resilience of electric power systems. This chapter addresses the online protection problem of power systems subject to disruptive disturbances caused by contingencies. A novel distributed optimization algorithm for flexible alternate current transmission systems devices is proposed to...

This paper presents a distributed multi-layer ring barrier coverage algorithm. In order to achieve single-layer ring barrier coverage, a distributed single-layer ring barrier coverage algorithm that maximises the probability of monitoring is proposed. Considering the security risks of single-layer barrier coverage, a distributed adjustment mechanis...

The responsive and effective pre-protective actions are vital to the resilience of electrical power systems. This paper addresses the online pre-protection problem of power systems subject to disruptive disturbances caused by contingencies. A novel distributed optimization algorithm for flexible alternate current transmission systems (FACTS) device...

It is always a challenging task to service sudden events in non-convex and uncertain environments, and multi-agent coverage control provides a powerful theoretical framework to investigate the deployment problem of mobile robotic networks for minimizing the cost of handling random events. Inspired by the divide-and-conquer methodology, this paper p...

This paper addresses the coverage control problem of multi-agent systems in the uncertain environment. With the aid of Voronoi partition, a distributed coverage control formulation of multi-agent system is proposed to complete the workload in uncertain environments. Driven by the gradient of thermal field, each agent is able to move around for clea...

The online small-signal stability assessment of electrical power grids is typically a challenging problem due to uncertainties and parameter variations of power system dynamics as well as the incurred high computational complexity. This paper proposes a novel theoretical framework for dynamic small-signal stability assessment of power grids by esti...

Complex systems consist of various interconnected components, and they normally display peculiar behaviors. Since individual components interact with each other, the causality is quite complicated. Therefore, it is crucial to reveal the underlying principle of collective behaviors. As one of key research fields, multi-agent systems have attracted s...

In this chapter, we consider workload partition problems in order to dynamically sweep an uncertain region by multiple mobile agents. A distributed algorithm for mobile agents is designed to yield equal workload in each subregion by partitioning the entire region in real time. Due to the uncertainty in the region, the agents do not have the global...

This chapter discusses decentralized sweep coverage of a given region with parametric uncertainties by multiple agents. With parametric uncertainty in the environment, we present an adaptive sweep coverage algorithm to guarantee the region coverage by simultaneously sweeping the region and partitioning the workload. The adaptive technique with pers...

This chapter addresses a sweep coverage problem of multi-agent systems with general network topologies. To deal with environmental uncertainties, we present discrete-time sweep coverage algorithms to guarantee the complete coverage of the given region by sweeping in parallel with workload partition. Moreover, the error between actual coverage time...

In this chapter, we present a simple yet effective routing strategy inspired by coverage control, which delays the onset of congestion on traffic networks by introducing a control parameter. The routing algorithm allows a trade-off between the congestion level and the distance to the destination. Numerical verification of the coverage control strat...

This chapter proposes a coverage-based formulation for the interception problem against supersonic fight vehicles with multiple decoys. A cooperative guidance algorithm is designed to deploy a team of interceptors for maximizing the interception probability. In addition, an optimal control approach is developed to drive the interceptors for arrivin...

This chapter addresses the sweep coverage problem of MAS in the uncertain environment. A novel formulation of distributed sweep coverage is proposed for multiple agents to cooperatively complete the workload in the coverage region. To save the sweep time, each agent takes part in partitioning the whole region using its partition bar while sweeping...

This chapter summarizes main results on cooperative coverage control of MAS by reviewing theoretical formulation of multi-agent coverage control and its practical applications and then discusses possible research directions in the future, which include wide-area cooperative coverage control via UAV-Satellite coordination, coverage control design fo...

This chapter addresses the coverage problem of multiple mobile agents in the uncertain environment. A new formulation is proposed for monitoring random events (e.g., forest fire, geohazard, avalanche) in the coverage region, the random events can be described by a probability density function. Meanwhile, a distributed control method is developed fo...

This chapter proposes a novel sweep coverage formulation for a multi-agent system to cover a region with uncertain workload density, and it provides a decentralized coverage algorithm based on the formulation. To achieve the coverage, the concerned region is divided into a finite number of stripes, and the algorithm incorporates two operations on s...

Cooperative sweep coverage of multiagent systems (MASs) has found broad applications in various fields. This article proposes a scheme to address the sweep coverage problem of MASs within uncertain environments. In the proposed formulation, the coverage region is divided into multiple stripes, of which each has the workload completed by MASs in seq...

In this work, an adaptive event-triggered control approach is developed for a virtual player (VP) to generate the human-like trajectories in the mirror game, a simple yet effective paradigm for studying interpersonal coordination. By taking into account individual motor signature, an online control algorithm is designed to produce joint improvised...

Limited phasor measurement unit (PMU) and varying signal strength levels make fast real-time transmission-line outage detection challenging. Existing approaches focus on monitoring nodal algebraic variables, i.e., voltage phase angle and magnitude. Their effectiveness is predicated on both strong outage signals in voltage and PMUs in the outage loc...

Due to the significant effect of time delays on social motor coordination, this work aims to inquire into the coordination mechanism of human joint actions from a control perspective by designing a feedback controller with individual motor signature. Therein the time-varying delay is taken into account to reflect the delay of human motor system in...

Cascading blackouts of power systems are normally activated by the initial disruptive contingencies under certain conditions. Effective identification of such disruptive contingencies is significant to ensure the reliability and resilience of power systems. This note focuses on the identification of the disruptive contingencies on branches that can...

Online transmission line outage detection over the entire network enables timely corrective action to be taken, which prevents a local event from cascading into a large scale blackout. Line outage detection aims to detect an outage as soon as possible after it happened. Traditional methods either do not consider the transient dynamics following an...

The closed-form fhan and Fast algorithms proposed in Chap. 3 were both derived for a discrete-time, double-integral system using the method of isochronic regions; they demonstrate that the solution for DTOC problem is not necessarily a bang-bang control. Also, instead of chattering, the DTOC can produce a smooth control signal that results in the p...

This book highlights cooperative coverage control approaches of multi-agent systems in uncertain environments and their applications in various fields. A novel theoretical formulation of multi-agent coverage is proposed to fulfill the coverage task via divide-and-conquer scheme. By taking workload partition and sweeping operations simultaneously, a...

Due to uncertainties and the complicated intrinsic dynamics of power systems, it is difficult to predict the cascading failure paths once the cascades occur. This makes it challenging to achieve the effective power system protection against cascading blackouts. By incorporating uncertainties and stochastic factors of the cascades, a Markov chain mo...

Time optimal control based tracking differentiator (TOC-TD) sets a weaker condition on the stability of the systems to be constructed (Han in IEEE Trans Ind Electron 56(3):900–906, 2009, [1], (Guo and Zhao in Active disturbance rejection control for nonlinear systems: an introduction. Wiley, 2016, [2]). Also, it has advantageous smoothness and nois...

Time optimal control (TOC) originated from servo control design problems in the 1950s (Hopkin in Trans Am Inst Electr Eng 70(1):631–639, 1951, [1]), (LaSalle in Proc Natl Acad Sci USA 45(4):573, 1959, [2]), and has drawn significant interests in the field of applied mathematics (LaSalle in Contributions to the theory of nonlinear oscillations, vol...

Real-time differentiation estimation of signals is commonly used in the feedback controller design, the fault detection and isolation and many other control related fields (Han in IEEE Trans Ind Electron 56(3):900–906, 2009, [1]), (Ríos et al. in Int J Control 90(2):218–230, 2017, [2]), (Vázquez et al. in IEEE Trans Control Syst Technol 24(5):1740–...

Real-time tracking filtering and differentiation estimation of signals are commonly used in the feedback control, the fault detection and isolation and many other fields. In previous work, we have introduced the discrete time optimal control based tracking differentiator in detail.

Phasor Measurement Unit (PMU) technology is increasingly used for real-time monitoring applications, especially line outage detection and identification (D&I) in the power system. Current outage D&I schemes either assume a full PMU deployment or a partial deployment with fixed PMU placement. However, the placement of the PMUs has a fundamental impa...

IEEE Transactions on Power Systems: Online transmission line outage detection over the entire network enables timely corrective action to be taken, which prevents a local event from cascading into a large scale blackout. Line outage detection aims to detect an outage as soon as possible after it happened. Traditional methods either do not consider...

Cascading failures in power systems normally occur as a result of initial disturbances or faults on electrical elements, closely followed by situational awareness errors of human operators. It remains a great challenge to systematically trace the source of cascading failures in power systems. In this paper, we develop a mathematical model to descri...

In this paper, the problem of distributed output consensus is investigated for heterogeneous multi-agent systems subject to a class of uncertainties in communication channels. The studied uncertainties, leading to a time-varying communication topology modeled as a Markovian switching communication topology and delayed transit information, may happe...

Due to the evolving nature and the complicated coupling relationship of power system components , it has been a great challenge to identify the disruptive contingencies that can trigger cascading blackouts. This paper aims to develop a generic approach for identifying the initial disruptive contingencies that can result in the catastrophic cascadin...

Due to the evolving nature of power grids and model uncertainty, the online stability assessment of electrical power systems is always a challenging problem. This paper aims to provide a theoretical framework for estimating the region of attraction for power systems in real time. By analyzing and learning the measurement data in a given time durati...

Accepted by PMAPS 2020: Phasor Measurement Unit (PMU) technology is increasingly used for real-time monitoring applications, especially line outage detection and identification (D&I) in the power system. Current outage D&I schemes either assume a full PMU deployment or a partial deployment with fixed PMU placement. However, the placement of the PM...

In this paper, controllability of Markovian jump Boolean control networks (MJBCNs) is studied via semi-tensor product of matrices. First, based on the algebraic expression of the considered Boolean control networks, a necessary and sufficient condition for controllability is presented by iteration equations, which however may lead to high-dimension...

Due to uncertainties and the complicated intrinsic dynamics of power systems, it is difficult to predict the cascading failure paths once the cascades occur. This makes it challenging to achieve the effective power system protection against cascading blackouts. By incorporating uncertainties and stochastic factors of the cascades, a Markov chain mo...

Differential signals play significant roles in control practices, but they are prone to noise corruption. A noise-tolerant time-optimal system-based tracking differentiator (TD) was first proposed by Jingqing Han, which is constructed in the form of state feedback control for a discrete-time, double-integral system. However, its performances of sig...

This paper introduces a novel framework to construct the region of attraction (ROA) of a power system centered around a stable equilibrium by using stable state trajectories of system dynamics. Most existing works on estimating ROA rely on analytical Lyapunov functions, which are subject to two limitations: the analytic Lyapunov functions may not b...

Potential critical risks of cascading failures in power systems can be identified by exposing those critical electrical elements on which certain initial disturbances may cause maximum disruption to power transmission networks. In this work, we investigate cascading failures in power systems described by the direct current (DC) power flow equations...

Power system blackouts are usually triggered by the initial contingency and then deteriorate as the branch outage spreads quickly. Thus, it is crucial to eliminate the propagation of cascading outages in its infancy. In this paper, a model predictive approach is proposed to protect power grids against cascading blackout by timely shedding load on b...

An enhanced discrete-time tracking differentiator (TD)with high precision based on discrete-time optimal control (DTOC)law is proposed. This law takes the form of state feedback for a double-integral system that adopts the Isochronic Region approach. There, the control signal sequence is determined by a linearized criterion based on the position of...

Due to the evolving nature of power systems and the complicated coupling relationship of power devices, it has been a great challenge to identify the contingencies that could trigger cascading blackouts of power systems. This paper aims to develop a universal approach for identifying the initial disruptive contingencies that can result in the worst...

This paper addresses the sweep coverage problem of multi-agent systems in the uncertain environment. A novel formulation of distributed sweep coverage is proposed for multiple agents to cooperatively complete the workload in the coverage region. To save the sweep time, each agent takes part in partitioning the whole region using its partition bar w...

Due to the evolving nature of power systems and the complicated coupling relationship of power devices, it has been a great challenge to identify the contingencies that could trigger cascading blackouts of power systems. This paper provides an effective approach to identifying the initial contingency in power transmission networks, which are equipp...

This paper aims to investigate the risk identification problem of power transmission system that is integrated with renewable energy sources. In practice, the fluctuation of power generation from renewable energy sources can lead to severe consequences to power transmission network. By treating the fluctuation of power generation as the control inp...

In this work, an interactive control architecture based on velocity segments is developed to generate the human-like trajectories in the mirror game, a simple yet effective paradigm for studying interpersonal coordination, and the existence of velocity segments possessing a prescribed signature is theoretically guaranteed. Then an online control al...

This paper addresses the cooperative control problem of Thyristor-Controlled Series Compensation (TCSC) for eliminating the stress of cyber-physical power system. Specifically, the cyber-physical power system is composed of power transmission network, flexible alternate current transmission systems (FACTS) devices, phasor measurement unit (PMU), an...

In this brief, a novel tracking differentiator based on discrete time optimal control (DTOC) is presented. In particular, using the state back-stepping method, a DTOC law for a discrete-time, double-integral system is determined by linearized criterion, which equips the tracking differentiator with a simple structure. The analysis of the proposed t...

As an emerging research direction in the field of systems and control, distributed control or decentralized control has attracted great interests of researchers in the past decade. In this paper, a bibliometric analysis of the relevant publications is presented based on the data collected from the Science Citation Index Expanded Web of Science. In...

A discrete-time tracking differentiator (TD) based on a time criterion is presented. Its control law is derived by comparing the time that the initial state is driven to the switching curve or the origin with the sampling period. The advantages of this TD include faster signal-tracking, better noise filtering and derivative extraction. Simulation r...

This paper centers on the comparison of three different models that describe cascading failures of power systems. Specifically, these models are different in characterizing the physical properties of power networks and computing the branch power flow. Optimal control approach is applied on these models to identify the critical disturbances that res...

The convergence of a new closed-form solution for the discrete time optimal control is presented. First, a new time optimal control law with simple structure is constructed in the form of the state feedback for a discrete-time double-integral system by using the state backstepping approach. The control signal sequence in this approach is determined...

Rapid progress in the area of humanoid robots offers tremendous possibilities for investigating and improving social competences in people with social deficits, but remains yet unexplored in schizophrenia. In this study, we examined the influence of social feedbacks elicited by a humanoid robot on motor coordination during a human-robot interaction...

Cascading failures in power systems normally occur as a result of initial disturbance or faults on electrical elements, closely followed by errors of human operators. It remains a great challenge to systematically trace the source of cascading failures in power systems. In this paper, we develop a mathematical model to describe the cascading dynami...

Poster for Mid-term Review

Mirror game test could detect schizophrenia A new test of movement and social interaction could detect markers of schizophrenia, and help to diagnose and manage the condition. In an effort to establish reliable indicators of schizophrenia, Piotr Slowinski at the University of Exeter, UK and colleagues developed a test that could detect deficits in...

Extensive experiments in Human Movement Science suggest that solo motions are characterized by unique features that define the individuality or motor signature of people. While interacting with others, humans tend to spontaneously coordinate their movement and unconsciously give rise to joint improvisation. However, it has yet to be shed light on t...

Modeling the human movement of an upper limb has been a challenge in the past decades. Due to the complexity of the central nervous system (CNS) and the muscle structure, it is difficult to develop an accurate model that is able to repli-cate the dynamics of a human upper limb. Biomechanics provides a powerful framework to explore kinematic propert...

In this work we attempt to create a human-like virtual player able to play the mirror game with a human player in real time. A control architecture is developed in order to drive such virtual player to lead or track a human player during the game while maintaining a certain degree of similarity to its individual signature. The virtual player is abl...

This paper addresses the cooperative interception control problem of multiple interceptors to capture the mobile targets. Due to the measurement noise and decoys, the location of the real target is described by a probability density function (PDF). A coverage-based guidance algorithm and optimal control law are developed to maximize the probability...

Recent experiments demonstrate that rhythmic movements of human hand exhibit individual, idiosyncratic motion characteristics in the solo condition. It is undoubtedly promising to computationally produce the individualized hand movement for its great potential in motor rehabilitation. In this paper, we develop a computational approach that is able...

Joint improvisation is often observed among humans performing joint action tasks. Exploring the underlying cognitive and neural mechanisms behind the emergence of joint improvisation is an open research challenge. This paper investigates jointly improvised movements between two participants in the mirror game, a paradigmatic joint task example. Fir...