38,237 research outputs found
Distributed Optimal Control and Application to Consensus of Multi-Agent Systems
This paper develops a novel approach to the consensus problem of multi-agent
systems by minimizing a weighted state error with neighbor agents via linear
quadratic (LQ) optimal control theory. Existing consensus control algorithms
only utilize the current state of each agent, and the design of distributed
controller depends on nonzero eigenvalues of the communication topology. The
presented optimal consensus controller is obtained by solving Riccati equations
and designing appropriate observers to account for agents' historical state
information. It is shown that the corresponding cost function under the
proposed controllers is asymptotically optimal. Simulation examples demonstrate
the effectiveness of the proposed scheme, and a much faster convergence speed
than the conventional consensus methods. Moreover, the new method avoids
computing nonzero eigenvalues of the communication topology as in the
traditional consensus methods
Supportive consensus
[EN] The paper is concerned with the consensus problem in a multi-agent system such that each agent has boundary constraints. Classical Olfati-Saber's consensus algorithm converges to the same value of the consensus variable, and all the agents reach the same value. These algorithms find an equality solution. However, what happens when this equality solution is out of the range of some of the agents? In this case, this solution is not adequate for the proposed problem. In this paper, we propose a new kind of algorithms called supportive consensus where some agents of the network can compensate for the lack of capacity of other agents to reach the average value, and so obtain an acceptable solution for the proposed problem. Supportive consensus finds an equity solution. In the rest of the paper, we define the supportive consensus, analyze and demonstrate the network's capacity to compensate out of boundaries agents, propose different supportive consensus algorithms, and finally, provide some simulations to show the performance of the proposed algorithms.The author(s) received specific funding for this work from the Valencian Research Institute for Artificial Intelligence (VRAIN) where the authors are currently working. This work is partially supported by the Spanish Government project RTI2018-095390-B-C31, GVA-CEICE project PROMETEO/2018/002, and TAILOR, a project funded by EU Horizon 2020 research and innovation programme under GA No 952215. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Palomares Chust, A.; Rebollo Pedruelo, M.; Carrascosa Casamayor, C. (2020). Supportive consensus. PLoS ONE. 15(12):1-30. https://doi.org/10.1371/journal.pone.0243215S1301512Olfati-Saber, R., Fax, J. A., & Murray, R. M. (2007). Consensus and Cooperation in Networked Multi-Agent Systems. Proceedings of the IEEE, 95(1), 215-233. doi:10.1109/jproc.2006.887293Pérez, I. J., Cabrerizo, F. J., Alonso, S., Dong, Y. C., Chiclana, F., & Herrera-Viedma, E. (2018). On dynamic consensus processes in group decision making problems. Information Sciences, 459, 20-35. doi:10.1016/j.ins.2018.05.017Fischbacher, U., & Gächter, S. (2010). Social Preferences, Beliefs, and the Dynamics of Free Riding in Public Goods Experiments. American Economic Review, 100(1), 541-556. doi:10.1257/aer.100.1.541Du, S., Hu, L., & Song, M. (2016). Production optimization considering environmental performance and preference in the cap-and-trade system. Journal of Cleaner Production, 112, 1600-1607. doi:10.1016/j.jclepro.2014.08.086Alfonso, B., Botti, V., Garrido, A., & Giret, A. (2013). A MAS-based infrastructure for negotiation and its application to a water-right market. Information Systems Frontiers, 16(2), 183-199. doi:10.1007/s10796-013-9443-8Rebollo M, Carrascosa C, Palomares A. Consensus in Smart Grids for Decentralized Energy Management. In: Highlights of Practical Applications of Heterogeneous Multi-Agent Systems. The PAAMS Collection. Springer; 2014. p. 250–261.Zhao, T., & Ding, Z. (2018). Distributed Agent Consensus-Based Optimal Resource Management for Microgrids. IEEE Transactions on Sustainable Energy, 9(1), 443-452. doi:10.1109/tste.2017.2740833Qiu, Z., Liu, S., & Xie, L. (2018). Necessary and sufficient conditions for distributed constrained optimal consensus under bounded input. International Journal of Robust and Nonlinear Control, 28(6), 2619-2635. doi:10.1002/rnc.4040Wei Ren, & Beard, R. W. (2005). Consensus seeking in multiagent systems under dynamically changing interaction topologies. IEEE Transactions on Automatic Control, 50(5), 655-661. doi:10.1109/tac.2005.846556Ren, W., & Beard, R. W. (2008). Distributed Consensus in Multi-vehicle Cooperative Control. Communications and Control Engineering. doi:10.1007/978-1-84800-015-5Knorn F, Corless MJ, Shorten RN. A result on implicit consensus with application to emissions control. In: 2011 50th IEEE Conference on Decision and Control and European Control Conference; 2011. p. 1299–1304.Roy, S. (2015). Scaled consensus. Automatica, 51, 259-262. doi:10.1016/j.automatica.2014.10.073Mo, L., & Lin, P. (2018). Distributed consensus of second-order multiagent systems with nonconvex input constraints. International Journal of Robust and Nonlinear Control, 28(11), 3657-3664. doi:10.1002/rnc.4076Wang, Q., Gao, H., Alsaadi, F., & Hayat, T. (2014). An overview of consensus problems in constrained multi-agent coordination. Systems Science & Control Engineering, 2(1), 275-284. doi:10.1080/21642583.2014.897658Xi, J., Yang, J., Liu, H., & Zheng, T. (2018). Adaptive guaranteed-performance consensus design for high-order multiagent systems. Information Sciences, 467, 1-14. doi:10.1016/j.ins.2018.07.069Fontan A, Shi G, Hu X, Altafini C. Interval consensus: A novel class of constrained consensus problems for multiagent networks. In: 2017 IEEE 56th Annual Conference on Decision and Control (CDC); 2017. p. 4155–4160.Hou, W., Wu, Z., Fu, M., & Zhang, H. (2018). Constrained consensus of discrete-time multi-agent systems with time delay. International Journal of Systems Science, 49(5), 947-953. doi:10.1080/00207721.2018.1433899Elhage N, Beal J. Laplacian-based consensus on spatial computers. In: AAMAS; 2010. p. 907–914.Cavalcante R, Rogers A, Jennings N. Consensus acceleration in multiagent systems with the Chebyshev semi-iterative method. In: Proc. of AAMAS’11; 2011. p. 165–172.Hu, H., Yu, L., Zhang, W.-A., & Song, H. (2013). Group consensus in multi-agent systems with hybrid protocol. Journal of the Franklin Institute, 350(3), 575-597. doi:10.1016/j.jfranklin.2012.12.020Ji, Z., Lin, H., & Yu, H. (2012). Leaders in multi-agent controllability under consensus algorithm and tree topology. Systems & Control Letters, 61(9), 918-925. doi:10.1016/j.sysconle.2012.06.003Li, Y., & Tan, C. (2019). A survey of the consensus for multi-agent systems. Systems Science & Control Engineering, 7(1), 468-482. doi:10.1080/21642583.2019.1695689Salazar, N., Rodriguez-Aguilar, J. A., & Arcos, J. L. (2010). Robust coordination in large convention spaces. AI Communications, 23(4), 357-372. doi:10.3233/aic-2010-0479Pedroche F, Rebollo M, Carrascosa C, Palomares A. On the convergence of weighted-average consensus. CoRR. 2013;abs/1307.7562
Sampling-Based Optimization for Multi-Agent Model Predictive Control
We systematically review the Variational Optimization, Variational Inference
and Stochastic Search perspectives on sampling-based dynamic optimization and
discuss their connections to state-of-the-art optimizers and Stochastic Optimal
Control (SOC) theory. A general convergence and sample complexity analysis on
the three perspectives is provided through the unifying Stochastic Search
perspective. We then extend these frameworks to their distributed versions for
multi-agent control by combining them with consensus Alternating Direction
Method of Multipliers (ADMM) to decouple the full problem into local
neighborhood-level ones that can be solved in parallel. Model Predictive
Control (MPC) algorithms are then developed based on these frameworks, leading
to fully decentralized sampling-based dynamic optimizers. The capabilities of
the proposed algorithms framework are demonstrated on multiple complex
multi-agent tasks for vehicle and quadcopter systems in simulation. The results
compare different distributed sampling-based optimizers and their centralized
counterparts using unimodal Gaussian, mixture of Gaussians, and stein
variational policies. The scalability of the proposed distributed algorithms is
demonstrated on a 196-vehicle scenario where a direct application of
centralized sampling-based methods is shown to be prohibitive
Tailoring Gradient Methods for Differentially-Private Distributed Optimization
Decentralized optimization is gaining increased traction due to its
widespread applications in large-scale machine learning and multi-agent
systems. The same mechanism that enables its success, i.e., information sharing
among participating agents, however, also leads to the disclosure of individual
agents' private information, which is unacceptable when sensitive data are
involved. As differential privacy is becoming a de facto standard for privacy
preservation, recently results have emerged integrating differential privacy
with distributed optimization. Although such differential-privacy based privacy
approaches for distributed optimization are efficient in both computation and
communication, directly incorporating differential privacy design in existing
distributed optimization approaches significantly compromises optimization
accuracy. In this paper, we propose to redesign and tailor gradient methods for
differentially-private distributed optimization, and propose two
differential-privacy oriented gradient methods that can ensure both privacy and
optimality. We prove that the proposed distributed algorithms can ensure almost
sure convergence to an optimal solution under any persistent and
variance-bounded differential-privacy noise, which, to the best of our
knowledge, has not been reported before. The first algorithm is based on
static-consensus based gradient methods and only shares one variable in each
iteration. The second algorithm is based on dynamic-consensus
(gradient-tracking) based distributed optimization methods and, hence, it is
applicable to general directed interaction graph topologies. Numerical
comparisons with existing counterparts confirm the effectiveness of the
proposed approaches
Defending distributed systems against adversarial attacks: consensus, consensus-based learning, and statistical learning
A distributed system consists of networked components that interact with each other in order to achieve a common goal. Given the ubiquity of distributed systems and their vulnerability to adversarial attacks, it is crucial to design systems that are provably secured. In this dissertation, we propose and explore the problems of performing consensus, consensus-based learning, and statistical learning in the presence of malicious components.
(1) Consensus: In this dissertation, we explore the influence of communication range on the computability of reaching iterative approximate consensus. Particularly, we characterize the tight topological condition on the networks for consensus to be achievable in the presence of Byzantine components. Our results bridge the gap of previous work.
(2) Consensus-Based Learning: We propose, to the best of our knowledge, consensus-based Byzantine-tolerant learning problems: Consensus-Based Multi-Agent Optimization and Consensus-Based Distributed Hypothesis Testing. For the former, we characterize the performance degradation, and design efficient algorithms that can achieve the optimal fault-tolerance performance. For the latter, we propose, as far as we know, the first learning algorithm under which the good agents can collaboratively identify the underlying truth.
(3) Statistical Learning: Finally, we explore distributed statistical learning, where the distributed system is captured by the server-client model. We develop a distributed machine learning algorithm that is able to (1) tolerate Byzantine failures, (2) accurately learn a highly complex model with low local data volume, and (3) converge exponentially fast using logarithmic communication rounds
COOPERATIVE AND CONSENSUS-BASED CONTROL FOR A TEAM OF MULTI-AGENT SYSTEMS
Cooperative control has attracted a noticeable interest in control systems
community due to its numerous applications in areas such as formation flying
of unmanned aerial vehicles, cooperative attitude control of spacecraft, rendezvous
of mobile robots, unmanned underwater vehicles, traffic control, data
network congestion control and routing. Generally, in any cooperative control
of multi-agent systems one can find a set of locally sensed information, a
communication network with limited bandwidth, a decision making algorithm,
and a distributed computational capability. The ultimate goal of cooperative
systems is to achieve consensus or synchronization throughout the team members
while meeting all communication and computational constraints. The
consensus problem involves convergence of outputs or states of all agents to
a common value and it is more challenging when the agents are subjected to
disturbances, measurement noise, model uncertainties or they are faulty.
This dissertation deals with the above mentioned challenges and has developed
methods to design distributed cooperative control and fault recovery
strategies in multi-agent systems. Towards this end, we first proposed a
transformation for Linear Time Invariant (LTI) multi-agent systems that facilitates
a systematic control design procedure and make it possible to use
powerful Lyapunov stability analysis tool to guarantee its consensus achievement.
Moreover, Lyapunov stability analysis techniques for switched systems
are investigated and a novel method is introduced which is well suited for designing
consensus algorithms for switching topology multi-agent systems. This
method also makes it possible to deal with disturbances with limited root mean
square (RMS) intensities. In order to decrease controller design complexity, a
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method is presented which uses algebraic connectivity of the communication
network to decouple augmented dynamics of the team into lower dimensional
parts, which allows one to design the consensus algorithm based on the solution
to an algebraic Riccati equation with the same order as that of agent.
Although our proposed decoupling method is a powerful approach to reduce
the complexity of the controller design, it is possible to apply classical pole
placement methods to the transformed dynamics of the team to develop and
obtain controller gains.
The effects of actuator faults in consensus achievement of multi-agent systems
is investigated. We proposed a framework to quantitatively study actuator
loss-of-effectiveness effects in multi-agent systems. A fault index is defined
based on information on fault severities of agents and communication network
topology, and sufficient conditions for consensus achievement of the team are
derived. It is shown that the stability of the cooperative controller is linked to
the fault index. An optimization problem is formulated to minimize the team
fault index that leads to improvements in the performance of the team. A numerical
optimization algorithm is used to obtain the solutions to the optimal
problem and based on the solutions a fault recovery strategy is proposed for
both actuator saturation and loss-of-effectiveness fault types.
Finally, to make our proposed methodology more suitable for real life scenarios,
the consensus achievement of a multi-agent team in presence of measurement
noise and model uncertainties is investigated. Towards this end, first
a team of LTI agents with measurement noise is considered and an observer
based consensus algorithm is proposed and shown that the team can achieve
H∞ output consensus in presence of both bounded RMS disturbance input and
measurement noise. In the next step a multi-agent team with both linear and
Lipschitz nonlinearity uncertainties is studied and a cooperative control algorithm
is developed. An observer based approach is also developed to tackle
consensus achievement problem in presence of both measurement noise and
model uncertainties
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