Leader-following formation control of multi-agent networks based on distributed observers

To investigate the leader-following formation control, in this paper we present the design problem of control protocols and distributed observers under which the agents can achieve and maintain the desired formation from any initial states, while the velocity converges to that of the virtual leader whose velocity cannot be measured by agents in real time. The two cases of switching topologies without communication delay and fixed topology with time-varying communication delay are both considered for multi-agent networks. By using the Lyapunov stability theory, the issue of stability is analysed for multi-agent systems with switching topologies. Then, by considering the time-varying communication delay, the sufficient condition is proposed for the multi-agent systems with fixed topology. Finally, two numerical examples are given to illustrate the effectiveness of the proposed leader-following formation control protocols.

Distributed Multicircular Circumnavigation Control for UAVs with Desired Angular Spacing

This paper addresses a multicircular circumnavigation control for UAVs with desired angular spacing around a nonstationary target.By defining a coordinated error relative to neighboring angular spacing,under the premise that target information is perfectly accessible by all nodes,a centralized circular enclosing control strategy is derived for multiple UAVs connected by an undirected graph to allow for formation behaviors concerning the moving target.Besides,to avoid the requirement of target’s states being accessible for each UAV,fixed-time distributed observers are introduced to acquire the state estimates in a fixed-time sense,and the upper boundary of settling time can be determined offline irrespective of initial properties,greatly releasing the burdensome communication traffic.Then,with the aid of fixed-time distributed observers,a distributed circular circumnavigation controller is derived to force all UAVs to collaboratively evolve along the preset circles while keeping a desired angular spacing.It is inferred from Lyapunov stability that all errors are demonstrated to be convergent.Simulations are offered to verify the utility of proposed protocol.

An overview on the designs of distributed observers in LTI multi-agent systems

With the rapid development of information technologies and cloud computing, sensor networks play an increasingly important role in our society. Over the past few decades, distributed observer theory has attracted unprecedented attention due to its wide potential applications in different areas. Meanwhile, various approaches and algorithms have been proposed and investigated. The design of distributed observers is one of the frontier topics of system and control research, which has the significant theoretical values and broad application prospects. This paper attempts to review the representative models and the corresponding approaches for distributed observer design in linear time-invariant(LTI) systems. Firstly, the research backgrounds and main advances of distributed observer designs are briefly reviewed. Then, recent results of distributed observer designs for discrete-time and continuous-time LTI multi-agent systems(MASs) are introduced in detail, respectively. Finally, the prospects and the future work directions of the design of distributed observers are put forward. The main purpose of this paper is to promote the emerging topic on the designs of distributed observers, with focuses on the interdisciplinary interest from technological sciences.

Distributed cooperative task planning algorithm for multiple satellites in delayed communication environment

Multiple earth observing satellites need to communicate with each other to observe plenty of targets on the Earth together. The factors, such as external interference, result in satellite information interaction delays, which is unable to ensure the integrity and timeliness of the information on decision making for satellites. And the optimization of the planning result is affected. Therefore, the effect of communication delay is considered during the multi-satel ite coordinating process. For this problem, firstly, a distributed cooperative optimization problem for multiple satellites in the delayed communication environment is formulized. Secondly, based on both the analysis of the temporal sequence of tasks in a single satellite and the dynamically decoupled characteristics of the multi-satellite system, the environment information of multi-satellite distributed cooperative optimization is constructed on the basis of the directed acyclic graph（DAG）. Then, both a cooperative optimization decision making framework and a model are built according to the decentralized partial observable Markov decision process（DEC-POMDP）. After that, a satellite coordinating strategy aimed at different conditions of communication delay is mainly analyzed, and a unified processing strategy on communication delay is designed. An approximate cooperative optimization algorithm based on simulated annealing is proposed. Finally, the effectiveness and robustness of the method presented in this paper are verified via the simulation.

Cooperative Target Tracking of Multiple Autonomous Surface Vehicles Under Switching Interaction Topologies

This paper is concerned with the cooperative target tracking of multiple autonomous surface vehicles(ASVs)under switching interaction topologies.For the target to be tracked,only its position can be measured/received by some of the ASVs,and its velocity is unavailable to all the ASVs.A distributed extended state observer taking into consideration switching topologies is designed to integrally estimate unknown target dynamics and neighboring ASVs'dynamics.Accordingly,a novel kinematic controller is designed,which takes full advantage of known information and avoids the approximation of some virtual control vectors.Moreover,a disturbance observer is presented to estimate unknown time-varying environmental disturbance.Furthermore,a distributed dynamic controller is designed to regulate the involved ASVs to cooperatively track the target.It enables each ASV to adjust its forces and moments according to the received information from its neighbors.The effectiveness of the derived results is demonstrated through cooperative target tracking performance analysis for a tracking system composed of five interacting ASVs.

Airborne Observations of Cloud Condensation Nuclei Spectra and Aerosols over East Inner Mongolia

A set of vertical profiles of aerosol number concentrations, size distributions and cloud condensation nuclei（CCN）spectra was observed using a passive cloud and aerosol spectrometer（PCASP） and cloud condensation nuclei counter, over the Tongliao area, East Inner Mongolia, China. The results showed that the average aerosol number concentration in this region was much lower than that in heavily polluted areas. Monthly average aerosol number concentrations within the boundary layer reached a maximum in May and a minimum in September, and the variations in CCN number concentrations at different supersaturations showed the same trend. The parameters c and k of the empirical function N = c S^kwere 539 and1.477 under clean conditions, and their counterparts under polluted conditions were 1615 and 1.42. Measurements from the airborne probe mounted on a Yun-12（Y12） aircraft, together with Hybrid Single-Particle Lagrangian Integrated Trajectory model backward trajectories indicated that the air mass from the south of Tongliao contained a high concentration of aerosol particles（1000–2500 cm^（-3）） in the middle and lower parts of the troposphere. Moreover, detailed intercomparison of data obtained on two days in 2010 indicated that the activation efficiency in terms of the ratio of NCCNto N_a（aerosols measured from PCASP） was 0.74（0.4 supersaturations） when the air mass mainly came from south of Tongliao, and this value increased to 0.83 on the relatively cleaner day. Thus, long-range transport of anthropogenic pollutants from heavily polluted mega cities,such as Beijing and Tianjin, may result in slightly decreasing activation efficiencies.

Attack-resilient Distributed Control for Islanded Single-/three-phase Microgrids Based on Distributed Adaptive Observers

This paper investigates the power sharing and voltage regulation issues of islanded single-/three-phase microgrids(S/T-MGs)where both sources and loads are unbalanced and the presence of adversarial cyber-attacks against sensors of distributed generator(DG)units is considered.Firstly,each DG unit is modeled as a heterogeneous linear dynamic agent with disturbances caused by sources and loads,then the problem is formulated as a distributed containment control problem.After that,to guarantee satisfactory power sharing and voltage control performance asymptotically achieved for the S/T-MGs,an attack-resilient distributed secondary control approach is developed by designing a distributed adaptive observer.With this approach,the effect of the cyber-attacks can be neutralized to ensure system stability and preserve bounded voltage synchronization.Simulation results are presented to demonstrate the effectiveness of the proposed control approach.

Multiple Unmanned Underwater Vehicles Consensus Control with Unmeasurable Velocity Information and Environmental Disturbances Under Switching Directed Topologies

A consensus algorithm proposed in the paper is applied to tackle remarkable problems of unmeasurable velocities,the environmental disturbances, and the limited communication environment for the multiple unmanned underwater vehicles(multi-UUVs). Firstly, for a complex nonlinear and coupled model of the unmanned underwater vehicle(UUV), a technique of feedback linearization is developed to transform the nonlinear UUV model into a secondorder integral UUV model. Secondly, to address the problem of the unavailable velocity information and environmental disturbances for the multi-UUVs system, we design a distributed extended state observer(DESO) to estimate the unmeasurable velocities and environmental disturbances using the relative position information. Finally,we propose a protocol based on the estimation information from the DESO and demonstrate that the multi-UUVs system with the switching directed topologies under the protocol can reach consensus asymptotically. The theoretical result proposed in the literature is verified by one numerical example.

Output-based adaptive distributed observer for general linear leader systems over periodic switching digraphs

In this paper,we present a sufficient condition for the exponential stability of a class of linear switched systems.As an application of this stability result,we establish an output-based adaptive distributed observer for a general linear leader system over a periodic jointly connected switching communication network,which extends the applicability of the output-based adaptive distributed observer from a marginally stable linear leader system to any linear leader system and from an undirected switching graph to a directed switching graph.This output-based adaptive distributed observer will be applied to solve the leader-following consensus problem for multiple double-integrator systems.

Adaptive distributed observer design for containment control of heterogeneous discrete-time swarm systems

This paper develops both adaptive distributed dynamic state feedback control law and adaptive distributed measurement output feedback control law for heterogeneous discrete-time swarm systems with multiple leaders.The convex hull formed by the leaders and the system matrix of leaders is estimated via an adaptive distributed containment observer.Such estimations will feed the followers so that every follower can update the system matrix of the corresponding adaptive distributed containment observer and the system state of their neighbors.The followers cooperate with each other to achieve leader-follower consensus and thus solve the containment control problem over the network.Numerical results demonstrate the effectiveness and computational feasibility of the proposed control laws.

Adaptive distributed observer and the cooperative control of multi-agent systems

The distributed observer approach has been an effective way to synthesise a distributed control law for a multi-agent system.However,this approach assumes that all the followers know the system matrix of the leader system,and this assumption may not be desirable in some applications.In this note,we will further introduce an adaptive distributed observer,which is able to estimate both the state and the system matrix of the leader and thus does not require that all the followers know the system matrix of the leader system.We will also point out some applications of the adaptive distributed observer to several cooperative control problems of multiagent systems such as the leader-following consensus problem,the cooperative output regulation problem and rendezvous and/or flocking.

Climate change and Aedes albopictus risks in China:current impact and future projection

Background Future distribution of dengue risk is usually predicted based on predicted climate changes using general circulation models(GCMs).However,it is difficult to validate the GCM results and assess the uncertainty of the predictions.The observed changes in climate may be very different from the GCM results.We aim to utilize trends in observed climate dynamics to predict future risks of Aedes albopictus in China.Methods We collected Ae.albopictus surveillance data and observed climate records from 80 meteorological stations from 1970 to 2021.We analyzed the trends in climate change in China and made predictions on future climate for the years 2050 and 2080 based on trend analyses.We analyzed the relationship between climatic variables and the prevalence of Ae.albopictus in different months/seasons.We built a classification tree model(based on the average of 999 runs of classification and regression tree analyses)to predict the monthly/seasonal Ae.albopictus distribution based on the average climate from 1970 to 2000 and assessed the contributions of different climatic variables to the Ae.albopictus distribution.Using these models,we projected the future distributions of Ae.albopictus for 2050 and 2080.Results The study included Ae.albopictus surveillance from 259 sites in China found that winter to early spring(November–February)temperatures were strongly correlated with Ae.albopictus prevalence(prediction accuracy ranges 93.0–98.8%)—the higher the temperature the higher the prevalence,while precipitation in summer(June–September)was important predictor for Ae.albopictus prevalence.The machine learning tree models predicted the current prevalence of Ae.albopictus with high levels of agreement(accuracy>90%and Kappa agreement>80%for all 12 months).Overall,winter temperature contributed the most to Ae.albopictus distribution,followed by summer precipitation.An increase in temperature was observed from 1970 to 2021 in most places in China,and annual change rates varied substantially from-0.22℃/year to 0.58℃/year among sites,with the largest increase in temperature occurring from February to April(an annual increase of 1.4–4.7℃ in monthly mean,0.6–4.0℃ in monthly minimum,and 1.3–4.3℃ in monthly maximum temperature)and the smallest in November and December.Temperature increases were lower in the tropics/subtropics(1.5–2.3℃ from February–April)compared to the high-latitude areas(2.6–4.6℃ from February–April).The projected temperatures in 2050 and 2080 by this study were approximately 1–1.5℃ higher than those projected by GCMs.The estimated current Ae.albopictus risk distribution had a northern boundary of north-central China and the southern edge of northeastern China,with a risk period of June–September.The projected future Ae.albopictus risks in 2050 and 2080 cover nearly all of China,with an expanded risk period of April–October.The current at-risk population was estimated to be 960 million and the future at-risk population was projected to be 1.2 billion.Conclusions The magnitude of climate change in China is likely to surpass GCM predictions.Future dengue risks will expand to cover nearly all of China if current climate trends continue.

Continuous leaderless synchronization control of multiple spacecraft on SO(3)

This paper presents a solution to the leaderless consensus of multiple spacecraft on SO(3)under a connected undirected graph.An algorithm is proposed to generate an undirected tree graph from a connected undirected communication topology.A distributed observer is designed to estimate the desired attitude and angular velocity for each spacecraft under the generated tree graph.An adaptive controller with a general connected undirected graph is developed to complete the synchronization task.Cases with zero and nonzero final angular velocities are considered.Theoretical proofs and numerical simulations are presented to demonstrate the effectiveness of the proposed controllers.