603 research outputs found
Distributed adaptive fault-tolerant leader-following formation control of nonlinear uncertain second-order multi-agent systems
This paper presents a distributed integrated fault diagnosis and accommodation scheme for leaderâfollowing formation control of a class of nonlinear uncertain secondâorder multiâagent systems. The fault model under consideration includes both process and actuator faults, which may evolve abruptly or incipiently. The timeâvarying leader communicates with a small subset of follower agents, and each follower agent communicates to its directly connected neighbors through a bidirectional network with possibly asymmetric weights. A local fault diagnosis and accommodation component are designed for each agent in the distributed system, which consists of a fault detection and isolation module and a reconfigurable controller module comprised of a baseline controller and two adaptive faultâtolerant controllers, activated after fault detection and after fault isolation, respectively. By using appropriately the designed Lyapunov functions, the closedâloop stability and asymptotic convergence properties of the leaderâfollower formation are rigorously established under different modes of the faultâtolerant control system
Defense and Tolerance Technique Against Attacks and Faults on Leader-Following Multi-USVs
This study explores the leader-following consensus tracking control issue of multiple unmanned surface vehicles (multi-USVs) in the presence of malicious connectivity-mixed attacks in the cyber layer, and concurrent output channel noises, sensor/actuator faults, and wave-induced disturbances in the physical layer. Sensor/actuator faults are initially modeled with unified incipient and abrupt features. Additionally, connectivity-mixed attacks are depicted using connectivity-paralyzed and connectivity-maintained topologies through nonoverlapping and switching iterations. The standardization and observer design in multi-USVs are incorporated to decouple the augmented dynamics and estimate unknown state, fault, and noise observations, and then a defense and fault-tolerant consensus tracking control approach is designed to accomplish the robustness to disturbances/noises, resilience to attacks, and tolerance to faults, simultaneously. The criteria for achieving leader-following exponential consensus tracking of multi-USVs with cyber-physical threats can be determined based on activation rate and attack frequency indicators. Comparative simulations outline the effectiveness and economy of the proposed defense and tolerance technique against sensor/actuator faults and cyber-attacks on multi-USVs
Cooperative Control Reconfiguration in Networked Multi-Agent Systems
Development of a network of autonomous cooperating vehicles has attracted significant
attention during the past few years due to its broad range of applications in areas
such as autonomous underwater vehicles for exploring deep sea oceans, satellite formations
for space missions, and mobile robots in industrial sites where human involvement
is impossible or restricted, to name a few. Motivated by the stringent specifications
and requirements for depth, speed, position or attitude of the team and the possibility
of having unexpected actuators and sensors faults in missions for these vehicles have
led to the proposed research in this thesis on cooperative fault-tolerant control design of
autonomous networked vehicles.
First, a multi-agent system under a fixed and undirected network topology and subject
to actuator faults is studied. A reconfigurable control law is proposed and the so-called
distributed Hamilton-Jacobi-Bellman equations for the faulty agents are derived. Then,
the reconfigured controller gains are designed by solving these equations subject to the
faulty agent dynamics as well as the network structural constraints to ensure that the
agents can reach a consensus even in presence of a fault while simultaneously the team
performance index is minimized.
Next, a multi-agent network subject to simultaneous as well as subsequent actuator
faults and under directed fixed topology and subject to bounded energy disturbances is considered. An Hâ performance fault recovery control strategy is proposed that guarantees:
the state consensus errors remain bounded, the output of the faulty system behaves
exactly the same as that of the healthy system, and the specified Hâ performance bound
is guaranteed to be minimized. Towards this end, the reconfigured control law gains
are selected first by employing a geometric control approach where a set of controllers
guarantees that the output of the faulty agent imitates that of the healthy agent and the
consensus achievement objectives are satisfied. Then, the remaining degrees of freedom
in the selection of the control law gains are used to minimize the bound on a specified
Hâ performance index.
Then, control reconfiguration problem in a team subject to directed switching topology
networks as well as actuator faults and their severity estimation uncertainties is considered.
The consensus achievement of the faulty network is transformed into two stability
problems, in which one can be solved offline while the other should be solved online
and by utilizing information that each agent has received from the fault detection and
identification module. Using quadratic and convex hull Lyapunov functions the control
gains are designed and selected such that the team consensus achievement is guaranteed
while the upper bound of the team cost performance index is minimized.
Finally, a team of non-identical agents subject to actuator faults is considered. A
distributed output feedback control strategy is proposed which guarantees that agents
outputsâ follow the outputs of the exo-system and the agents states remains stable even
when agents are subject to different actuator faults
Consensus of multi-agent systems with faults and mismatches under switched topologies using a delta operator method
© 2018 Elsevier B.V. This paper studies the consensus of multi-agent systems with faults and mismatches under switched topologies using a delta operator method. Since faults and mismatches can result in failure of the consensus even for a fixed topology with a spanning tree, how to reach a consensus is a complicated and challenging problem under such circumstances especially when part topologies have no spanning tree. Although some works studied the influence of faults and mismatches on the consensus, there is little work on reaching a consensus for the multi-agent systems with faults and mismatches. In this paper, we introduce the delta operator to unify the consensus analysis for continuous, discrete, or sampled systems under one framework. We develop the theories on the delta operator systems first and then apply theories of the delta operator systems to the consensus problems. By converting the consensus problems into stability problems, we investigate and prove consensus and the associated conditions for systems 1) without any fault, 2) with a known fault, and 3) with unknown faults, under switching topologies with matching or mismatching coefficients. Numerical examples are provided and validate the effectiveness of the theoretical results
Distributed Fault-Tolerant Control for Networked Robots in the Presence of Recoverable/Unrecoverable Faults and Reactive Behaviors
The paper presents an architecture for distributed control of multi-robot systems with
an integrated fault detection, isolation, and recovery strategy. The proposed solution is
based on a distributed observer-controller schema where each robot, by communicating
only with its direct neighbors, is able to estimate the overall state of the system; such
an estimate is then used by the controllers of each robot to achieve global missions
as, for example, centroid and formation tracking. The information exchanged among
the observers is also used to compute residual vectors that allow each robot to detect
failures on anyone of the teammates, even if not in direct communication. The proposed
strategy considers both recoverable and unrecoverable actuator faults as well as it
properly manages the possible activation of reactive local control behaviors of the
robots (e.g., the activation of obstacle avoidance strategy), which generate control inputs
different from those required by the global mission control. In particular, when the robots
are subject to recoverable faults, those are managed at a local level by computing a
proper compensating control action. On the other side, when the robots are subject to
unrecoverable faults, the faults are isolated from anyone of the teammates by means of a
distributed fault detection and isolation strategy; then, the faulty robots are removed from
the team and the mission is rearranged. The proposed strategy is validated via numerical
simulations where the system properly identifies and manages the different cases of
recoverable and unrecoverable actuator faults, as well as it manages the activation of
local reactive control in an integrated case study
Fault-tolerant Synchronization of Autonomous Underwater Vehicles
The main objective of this thesis is to develop a fault-tolerant and reconfigurable synchronization scheme based on model-based control protocols for stern and sail hydroplanes that are employed as actuators in the attitude control subsystem (ACS) of an autonomous underwater vehicle (AUV). In this thesis two control approaches are considered for synchronization, namely i) state feedback synchronization, and ii) output feedback synchronization. Both problems are tackled by proposing a passive control approach as well as an active reconfiguration (re-designing the control gains).
For the âstate feedbackâ synchronization scheme, to achieve consensus the relative/absolute measurements of the AUVâs states (position and attitude) are available. The states of a longitudinal model of an AUV are mainly heave, pitch, and their associated rates. For the state feedback problem we employ a static protocol, and it is shown that the multi-agent system will synchronize in the stochastic mean square sense in the presence of measurement noise. However, the resulting performance index defined as the accumulated sum of variations of control inputs and synchronization errors is high. To deal with this problem, Kalman filtering is used for states estimation that are used in synchronization protocol. Moreover, the eïżœffects of parameter uncertainty of the agentâs dynamics are also investigated through simulation results. By employing the static protocol it is
demonstrated that when a loss of eïżœffectiveness (LOE) or float fault occurs the synchronization can still be achieved under some conditions. Finally, one of the main problems that is tackled in the
state feedback scenario is our proposed proportional-integral (PI) control methodology to deal with the lock in place (LIP) fault. It is shown that if the LIP fault occurs, by employing a PI protocol
the synchronization could still be achieved. Finally, our proposed dynamic synchronization protocol methodology is applied given that the fault (LOE/float) severity is known. Since after a fault
occurrence the agents become heterogeneous, employing the dynamic scheme makes the task of reconfiguration (redesigning the gains) more eïżœffective.
For the âoutput feedbackâ synchronization approach, to achieve consensus relative/absolute measurements of the AUVâs states except the pitch rate are available. For the output feedback
problem a dynamic protocol through a Luenberger observer is first employed for state estimation and the synchronization achievement is demonstrated. Then, a system under state and measurement noise is considered, and it is shown that by employing a Kalman filter for the state estimation; the multi-agent system will synchronize in the stochastic mean square sense. Furthermore, by employing the static protocol, it is shown that when a LOE/float fault occurs the synchronization is still achieved under certain conditions. Finally, one of the main problems that is tackled in the output feedback scenario is our proposed dynamic controller methodology. The results of this scheme are compared with another approach that exploits both dynamic controller and dynamic observer. The former approach has less computational eïżœort and results in more a robust control with respect to the actuator fault. The reason is that the later method employs an observer that uses the control input matrix information. When fault occurs, this information will not be correct any more. However, if there is a need to redesign the synchronization gains under faulty scenario, the later methodology is preferred. The reason is that the former approach becomes complicated when there is a fault even though its severity is known.
In this thesis, fault-tolerant synchronization of autonomous underwater vehicles is considered. In the first chapter a brief introduction on the motivation, problem definition, objectives and the methodologies that are used in the dissertation are discussed. A literature review on research dedicated to synchronization, fault diagnosis, and fault-tolerant control is provided. In Chapter 2, a through literature review on unmanned underwater vehicles is covered. It also comprises a comprehensive background information and definitions including algebraic graph theory, matrix
theory, and fault modeling. In the problem statement, the two main problems in this thesis, namely state feedback synchronization and output feedback synchronization are discussed. Chapters 3 and 4 will cover these two problems, their solutions, and the corresponding simulation results that are provided. Finally, Chapter 5 includes a discussion of conclusions and future work
Adaptation Strategy for a Distributed Autonomous UAV Formation in Case of Aircraft Loss
Controlling a distributed autonomous unmanned aerial vehicle (UAV) formation
is usually considered in the context of recovering the connectivity graph
should a single UAV agent be lost. At the same time, little focus is made on
how such loss affects the dynamics of the formation as a system. To compensate
for the negative effects, we propose an adaptation algorithm that reduces the
increasing interaction between the UAV agents that remain in the formation.
This algorithm enables the autonomous system to adjust to the new equilibrium
state. The algorithm has been tested by computer simulation on full nonlinear
UAV models. Simulation results prove the negative effect (the increased final
cruising speed of the formation) to be completely eliminated
Formation Control and Fault Accommodation for a Team of Autonomous Underwater Vehicles
The purpose of this thesis is the development of efficient formation control and fault accommodation algorithms for a team of autonomous underwater vehicles (AUVs). The team of AUVs are capable of performing a wide range of deep water marine applications such as seabed mapping and surveying, oil and gas exploration and extraction, and oil and gas pipeline inspection. However, communication limitations and the presence of undesirable events such as component faults in any of the team members can prevent the whole team to achieve safe, reliable, and efficient performance while executing underwater mission tasks.
In this regard, the semi-decentralized control scheme is developed to achieve trajectory tracking and formation keeping while requiring information exchange only among neighboring agents. To this end, model predictive control (MPC) technique
and dynamic game theory are utilized to formulate and solve the formation control problem. Moreover, centralized and decentralized control schemes are developed to assess the performance of the proposed semi-decentralized control scheme in the simulation studies. The simulation results verify that the performance of the proposed semi-decentralized scheme is very close to the centralized scheme with lower control effort cost while it does not impose stringent communication requirements as in the centralized scheme.
Moreover, the semi-decentralized active fault recovery scheme is developed to maintain a graceful degraded performance and to ensure that the team of autonomous underwater vehicles can satisfy mission objectives when an actuator fault occurs in
any of the team members. In this regard, online fault information provided by fault detection and isolation (FDI) modules of each agent and its neighbors are incorporated to redesign the nominal controllers based on the MPC technique and dynamic game theory. Additionally, FDI imperfections such as fault estimation error and time delay are taken into account, and a performance index is derived to show the impact of FDI imperfections on the performance of team members. Moreover, centralized and decentralized active fault recovery schemes are developed to evaluate the performance of the proposed semi-decentralized recovery scheme through comparative simulation studies with various fault scenarios. The comparative simulation studies justify that the proposed semi-decentralized fault recovery scheme meets the design specifications even if the performance of the FDI module is not ideal
- âŠ