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 H∞ 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 H∞ 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 H∞ 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 outputs’ follow the outputs of the exo-system and the agents states remains stable even when agents are subject to different actuator faults

The effect of herbal supplement and exercise training on plasma lipid profile in diabetic male rats

The present study was conducted to investigate the effect of six weeks of intermittent exercise and curcumin consumption on the lipid profile of diabetic male rats. In an experimental trial, 30 male Wistar rats were randomly divided into six groups (5 rats in each group): control, diabetic, healthy intermittent exercise, intermittent exercise +diabetes, curcumin +diabetes and curcumin+ exercise +diabetes. Diabetes was induced by intraperitoneal injection of streptozotocin poison (50 mg/kg). Intermittent training consisted of 5-12 bouts of intense work (75 to 100% of maximum speed) of 60 seconds with active rest intervals of 75 seconds, six days a week for six weeks. Curcumin was fed to animals by gavage at a dose of 50 mg per kilogram of body weight. After six weeks, unconscious animals and blood samples were collected from their hearts. The data were analyzed using ANOVA statistical test and Bonferroni post hoc test. Induction of diabetes caused an increase in cholesterol, TG and LDL levels (P=0.01). Intermittent training and curcumin, each alone, caused them to decrease (P=0.01). In addition, diabetes decreased HDL while intermittent exercise increased it, but curcumin supplementation did not have a significant effect. The effect of combining interval training with curcumin supplement was significant only for TG and did not have a significant effect on other data. Exercise training and curcumin can have an anti-inflammatory effect with reducing lipid profile and increasing HDL in diabetic animal

Effect of six weeks of interval training and curcumin consumption on apolipoprotein A and B in diabetic male rats

The present study was conducted to investigate the effect of six weeks of intermittent exercise and curcumin consumption on plasma Apo A and Apo B concentrations in male Wistar rats. 30 male Wistar rats were randomly divided into six groups (5 rats in each group): control, diabetic, healthy intermittent exercise, intermittent exercise diabetes, curcumin diabetes and curcumin exercise diabetes. Diabetes was induced by intraperitoneal injection of streptozotocin poison (50 mg/kg). Intermittent training consisted of 5-12 bouts of intense work (75 to 100% of maximum speed) of 60 seconds with active rest intervals of 75 seconds, six days a week for six weeks. Curcumin was fed to animals by gavage at a dose of 50 mg per kilogram of body weight. The results demonstrated that diabetes induction significantly decreased plasma Apo A concentration (p≤0.01) and increased plasma Apo B concentration (p≤0.01). Intermittent training caused a significant increase in Apo A and a significant decrease in Apo B plasma in diabetic rats. Also, it was found that six weeks of curcumin consumption significantly increased the concentration of Apo A in plasma and decreased the concentration of Apo B and the ratio of Apo B to Apo A (p≤0.01). At end, the results of the present study showed that intermittent exercise, curcumin and the combination of two interventions improve the disorders caused by diabetes in apolipoproteins

Online State Space Model Parameter Estimation in Synchronous Machines

The purpose of this paper is to present a new approach based on the Least Squares Error method for estimating the unknown parameters of the nonlinear 3rd order synchronous generator model. The proposed method uses the mathematical relationships between the machine parameters and on-line input/output measurements to estimate the parameters of the nonlinear state space model. The field voltage is considered as the input and the rotor angle and the active power are considered as the generator outputs. In fact, the third order nonlinear state space model is converted to only two linear regression equations. Then, easy-implemented regression equations are used to estimate the unknown parameters of the nonlinear model. The suggested approach is evaluated for a sample synchronous machine model. Estimated parameters are tested for different inputs at different operating conditions. The effect of noise is also considered in this study. Simulation results show that the proposed approach provides good accuracy for parameter estimation

Suboptimal control reconfiguration in switched multi-agent networked systems

In this work, the control recovery problem in a directed network of switched multi-agent systems is studied. A distributed cooperative control strategy is proposed which ensures that the agents reach a consensus while the upper bound of the team performance index is minimized even when the agents are subject to actuator faults where fault severity estimation uncertainties are presented. Using quadratic Lyapunov functions, a reconfiguration strategy is provided to design the gains of the proposed distributed reconfigurable control laws such that the team objectives are guaranteed. Our proposed reconfigurable control laws are applied to a team of seven autonomous underwater vehicles under directed switching topology and subject to simultaneous actuator faults. Simulation results demonstrate the effectiveness of the proposed reconfiguration control laws in compensating for the effects of sudden actuator faults and uncertainties. 2016 American Automatic Control Council (AACC).Scopu

Cost performance based control reconfiguration in multi-agent systems

In this paper, a reconfigurable control protocol for a linear multi-agent system seeking consensus in presence of actuator faults and saturations is investigated. The control protocol consists of two parts: healthy system controller and faulty system controller. The main objective of the healthy controller that is designed off-line is to determine the protocol which guarantees team consensus and minimizes the team performance index. On the other hand, the faulty system controller is designed on-line and aims at stabilizing the consensus error signals and optimizing the faulty team performance index subject to constrained input signals. Both centralized and semi-distributed architectures for control reconfiguration are developed. In the centralized scheme, the team is considered as a single unit and the central module reconfigures the entire system controllers, while in the semi-distributed approach faulty agent uses its immediate neighbours information (i.e. measurements and control gains) to reconfigure its controller. 2014 American Automatic Control Council.Qatar National Research FundScopu

A Distributed Control Reconfiguration and Accommodation for Consensus Achievement of Multiagent Systems Subject to Actuator Faults

This paper tackles the development of distributed control reconfiguration and fault accommodation strategies for consensus achievement in multiagent systems in the presence of faulty agents whose actuators are unable to produce their nominal control efforts. A faulty agent can adversely affect and prevent the team from reaching agreement and lead to catastrophic mission performance degradations. To ensure that the faulty team pursues its consensus objectives, in this paper, on-line distributed control reconfiguration strategies are developed that employ only nearest neighbor information to guarantee the team consensus while minimizing a local cost performance index. Toward the above end, the distributed Hamilton-Jacobi-Bellman equations for the faulty agent are derived and novel reconfigured controllers are designed by solving the above equations subject to the faulty agent dynamics and network structure constraints to ensure fault accommodation of the entire team. Our proposed reconfigurable controllers are applied to a network of autonomous underwater vehicles subject to actuator faults to demonstrate and illustrate the effectiveness and capabilities of our proposed fault recovery control strategies.This work was supported by the Qatar National Research Fund (a member of Qatar Foundation) through the National Priorities Research Program under Grant 5-045-2-017.Scopu

Distributed reconfigurable control strategies for switching topology networked multi-agent systems

In this paper, distributed control reconfiguration strategies for directed switching topology networked multi-agent systems are developed and investigated. The proposed control strategies are invoked when the agents are subject to actuator faults and while the available fault detection and isolation (FDI) modules provide inaccurate and unreliable information on the estimation of faults severities. Our proposed strategies will ensure that the agents reach a consensus while an upper bound on the team performance index is ensured and satisfied. Three types of actuator faults are considered, namely: the loss of effectiveness fault, the outage fault, and the stuck fault. By utilizing quadratic and convex hull (composite) Lyapunov functions, two cooperative and distributed recovery strategies are designed and provided to select the gains of the proposed control laws such that the team objectives are guaranteed. Our proposed reconfigurable control laws are applied to a team of autonomous underwater vehicles (AUVs) under directed switching topologies and subject to simultaneous actuator faults. Simulation results demonstrate the effectiveness of our proposed distributed reconfiguration control laws in compensating for the effects of sudden actuator faults and subject to fault diagnosis module uncertainties and unreliabilities. 1 2017 ISAScopu

An H∞ cooperative fault recovery control of multi-agent systems

In this work, an H∞ performance fault recovery control problem for a team of multi-agent systems that is subject to actuator faults is studied. Our main objective is to design a distributed control reconfiguration strategy such that in presence of actuator faults, (a) the state consensus errors remain bounded, (b) the outputs of the faulty team behave exactly the same as that of the healthy team, and (c) the specified H∞ performance bound is guaranteed to be minimized in presence of bounded energy disturbances. The reconfigured control law gains are selected first by employing a geometric approach where a set of controllers guarantees that the output of the faulty agent imitates that of the healthy agent and that the consensus achievement objectives are satisfied. Next, the remaining degrees of freedom in selection of the control law gains are utilized to minimize the bound on a specified H∞ performance index. Finally, the effects of uncertainties and imperfections in the FDI module decision in estimating the fault severity are investigated and a bound on the maximum tolerable estimation uncertainties is obtained. Keywords: Multi-agent systems; Actuator faults; Cooperative fault recovery; Consensus achievement; Disturbance attenuationScopu

Control reconfiguration for multiple autonomous vehicles subject to actuator faults and disturbances

In this paper, control reconfiguration problem in a team of multi-agent systems subject to actuator faults and environmental disturbances is studied. The proposed distributed control strategy has the capability of being reconfigured by using local information when a fault is detected and identified. It ensures that in absence of disturbances the faulty agent errors remain bounded while its output behaves exactly the same as that of the healthy system. Moreover, the specified H? performance bound is guaranteed to be minimized in presence of bounded energy disturbances. Towards this end, first by employing a geometric approach a set of control gains are obtained that enforce the output of the faulty agent imitates that of the healthy agent while the consensus achievement objectives are satisfied. Next, the remaining degrees of freedom in the selection of the control law gains are used to minimize the bound on a specified H? performance index. Our proposed distributed and cooperative control recovery approach is applied to a team of autonomous underwater vehicles to demonstrate its effectiveness in accomplishing the overall team requirements. 2016 American Automatic Control Council (AACC).Scopu