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 iii 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

QFT Controller Design for Uncertain Multivariable Linear Systems With Constraint on Bandwidth, With the Aid of an Internal Feedback

Based on the explained and proved theorems, this paper presents a new robust QFT controller design for uncertain multivariable linear systems with hard time-domain constraints on their output signals, as well as constraints on their bandwidth. In this method, the multivariable process is converted to a new process using an internal feedback and diagonal controller. With the aid of basically non-interacting(BNI) method in QFT, the resulting process is devided into several SISO systems and proper controllers is then designed by QFT. Controller transfer function matrix is diagonal, therefore, desired bandwidth can be acquired. Finally a comparison of the proposed method and the conventional QFT method, as well as its application, is shown in an example

Zagros Team Research Proposal

Zagros team is consisted of a group of interested students in Robocup soccer simulation. Team started work in October 2006 by designing and developing a new 3D soccer simulation agent structure from the scratch. During a 6 month period of hard work and research many goals were achieved. By announcing new Robocup rules for simulation league, team immediately started work on humanoids and so far has completed the research and development outline for the upcoming competitions. Apart from the members' interest in the field, and their previous experiences, an adaptive learning approach for optimizing biped robot walk model has been chosen as the title of some of the members' B.S. thesis. In this paper a rough draft of team's planned research approach and previous achievements is described. Previous Works Team started working on soccer simulation as newcomers under the name of Zagros since October 2006, but members were involved in Robocup community individually far before the above date. To ease the primary task of development and debugging and also better observing and analyzing agents' behavior, a Linux-based trainer and a complete windows online debugger, capable of sending and receiving commands to and from agents and simulation server, were written. Problems with synchronizing agents with spades information were solved by means of an event based structure for updating the agents' world model. A modified version of Kalman filter was implemented in order to get an accurate estimation of position and vision noise reduction. Average agent localization noise of about 4 centimeters was achieved in a complete match which is the most accurate result among competitors as far as published papers demonstrate. By announcing the new simulation league rules, members changed their research and development focus to humanoid model, bringing all the experience and achievements to the new domain