Sharif Digital Repository

An Ad-Hoc wireless network consists of a collection of geographically distributed nodes that communicate with each other over a wireless medium. These networks don’t use any infrastructure or base station to channel allocation. The important difference between wireless networks and wired networks is the broadcast nature of wireless communications. In these networks, each node transmits data to all of the nodes in the transmission range which may cause an increase in interference and data loss. On the other hand, due to mobility of users, fading the channel between them and change of routing, the probability of data loss increases. The extensive and successful employment of TCP variants in... 

dFlocking in multi-agent systems as one of the most interested phenomena has gained scientists and researchers attention in recent years. In a multi-agent system, agents by using a consensus algorithm, which designed based on collective, collision avoidance, and velocity adaption rules, try to catch a common goal together. The aims which may define for flocking of a multi-agent system include the getting a certain point, chasing an alien agent, moving in a given route, and so on. Without considering flock’s purposes, all agents must be aware about the goal to catch it. But it is not possible always to inform all agents about the goal. Because sending the goal information to all agents due to... 

Cooperative system is a system in which agents jointly try to reach a common goal. In order to achieve the desirable goal, a cooperative system needs some conditions such as agents moving as a flock and avoiding to conflict with each other and obstacles. Collision avoidance is one of the most important and notable factor in cooperative systems. This issue has been addressed by many researchers and different solutions have been proposed so far. In this thesis, existing methods and algorithms are studied. Among these algorithms two well-known ones have been investigated having considered their advantages and disadvantages in more detail. Some improvements on these two algorithms are proposed... 

In recent years, increasing attention has been paid to the fractional calculus as a powerful tool for more precise modeling of real world phenomena. Also, it has been shown that using this tool in designing control systems results in controllers that are more efficient in comparison with their traditional integer order counterparts. In spite of the advantages of fractional order models, the difficulties in the implementation of this type of models are still the main concern of the control system community. Clearly, as a model becomes simpler, its implementation becomes more convenient. Therefore, one way to rectify the implementation problems is to model the intended system as simple as... 

The constrained nonlinear systems with large operating regions have attracted great attention due to their correspondence with the most practical systems. There are several tools such as gain scheduling and Nonlinear Model Predictive Control (NMPC) to control them. Gain scheduling, with ability to provide stability guarantees between the estimated stability regions overlapping each other and to cover a large space of the allowable operating range of the system, is an attractive practical approach to control the systems with large operating regions. But this strategy do not account for constraints explicitly by online optimization. On the contrary, NMPC handles constraints on the manipulated... 

A group of vehicles are contributed to follow static or dynamic targets in a cooperative target tracking problem. The vehicles estimate the future location of dynamic targets based on the information they receive from other vehicles and targets. Noting to these estimations, the vehicles are able to decide the best movement toward the targets. Various control methods have been presented to solve different problems of target tracking which the majority of them proposed optimal control solutions. A new approach to the problem of tracking dynamic targets via cooperative multi-vehicle systems under the receding horizon control of the vehicles is proposed in this dissertation. A receding horizon... 

One of usual criterion which detrimines how much two polynomials are close to each other is smallness of the norm of vector that is formed from subtraction of their corresponding coefficients. Using this criterion, in this dissertation we become involved in investigation of two similar problems. First one is determination of the closest non-Hurwitz polynomial to a Hurwitz one. During this activity, the robustness margin of Hurwitz polynomial whose coefficients are subject to uncertainty is determined. The second problem is determination of the closest Hurwitz polynomial to another polynomial which is not Hurwitz. Unlike to the first problem, this problem is extremely hard. The solution of... 

Cooperative control of autonomous multi-agent systems is one of the challenging problems in control theory. According to existing enhancements in communication networks and broad application of multi-agent systems in various engineering fields, coordinated motion control in multi-agent systems has been attracted the attention of researchers in control science. In this thesis, flocking algorithms in multi-agent systems with undirected interactions (bidirectional information flow) is considered and new convergence results and final characteristics are obtained. Also, geometric optimization methods are used to propose a new optimization problem to reduce the number of informed agents of the... 

An algebraic method is presented for assessing the bounded input bounded output (BIBO) stability of a class of fractional delay systems with commensurate orders and multiple commensurate delays of retarded type. In the proposed method, first, by mapping the principal sheet of the Riemann surface and a pseudo-delay transformation, an auxiliary polynomial is generated. Then, this auxiliary polynomial is employed to find roots of the characteristic equation on the imaginary axis. The properties of the root path close to these roots are used to identify intervals of delay values, in which the system is stable. Moreover, a delay-independent BIBO-stability criterion is provided. Based on the... 

In this thesis, a new general state space form for uncertain LTI-fractional order system subjected to interval and polytopic uncertainties is introduced. Robust stability analysis and robust stabilization of presented system are investigated. Fractional derivative order assumed to be a known constant. Sufficient conditions in terms linear matrix inequalities (LMIs) are concluded to check the robust stability of the presented system. Then, these results are extended to derive some sufficient LMI conditions to design a state feedback controller in order to stabilize the mentioned uncertain system robustly. Effectiveness and correctness of presented sufficient conditions and application of... 

This thesis deals with identification of Errors-In-Variable(EIV) models with Compensated Prediction Error Method (CPEM). In EIV model structure, noise affects both on input and output data. We introduce a method to identify linear and discrete EIV models where the conventional PEM in classical identification, has been used in. Using PEM on EIV models leads to a biased estimation. Therefore, the reason of incorrect estimationobtained from PEM in the presence of input noise is investigated and the importance of consideringthe input noise is explained. Then by introducing two modifications, we try to compensate the deficiencies caused due to the presence of input noise. First, some changes are... 

Fault occurrence is an inevitable problem in industrial plants. These faults have numerous types. Some common kinds of faults are faults in actuators, faults in system dynamics, and faults in sensors. In many cases it is not possible to change or repair the broken part immediately. On the other hand, it is not reasonable to shut-down the whole system due to a minor failure. Therefore we should take a measure to have the best output possible in a faulty plant. In this thesis we have proposed a new static compensator by which we distribute the contribution of the faulty actuator among the other ones. At the end we evaluate the method by means of simulations  

First, stabilization problem of an integer order-nonlinear differential inclusion (IO-NDI) in the form of tracking problem is investigated and discussed while control inputs are subjected to the sector and dead-zone nonlinearities. Based on two the well-known theorems, the mentioned differential inclusion is modeled by a nonlinear system possessing polytopic uncertainties. For tackling the mentioned problem, sliding mode control (SMC) approach is applied and developed. Second, two issues including stability analysis and stabilization problem of a fractional order-linear differential inclusion (FO-LDI) are studied for both fractional order derivatives and separately. For solving these... 

Time delay generates exponential transcendental terms in characteristic equations. Subsequently, the applied methods are narrow to assess the stability map of delayed fractional-order systems with vanishing fractions. In this case, it is convenient to approximate these equations with its integer-order counterparts to design controllers or investigating features of the systems. But, delay can cause enormous differences between characteristic of these two equations. This study offers a method to survey analytically the stability of fractional-order time delayed linear time invariant systems with infinitesimal fractions. In this method, equations are transferred to an explicit expression which... 

In this thesis, two essential issues are investigated. The first issue is, when a general incommensurate fractional-order controller would be a stabilizing controller for an incommensurate fractional-order system in the standard feedback structure, and how one can possibly construct such closed-loop stabilizing controller. The second issue is to synthesize internal model principle based fractional-order controllers. These controllers consist of two main parts: the internal model corresponding to exogenous signals and an arbitrary fractional order controller. The main objective in the internal model principle based controllers, is to synthesize the second part of the controller such that the... 

Gas Metal Arc Welding (GMAW) process is one of the most applicable component in the industry due to its high speed and capability of employing for wide ranges of materials. The quality of products in a welding process is relevant to the quality of welding which is determined by characteristics like shape and size of droplet during detachment. In order to improve the quality of welding, a precise model of the process is required. There are many various model presented for GMAW process based on its dynamic equations. Almost all of these models assume the process as a continuous state system. However the process includes sudden variants in droplet detachment that is known as hybrid behavior.... 

Delay is an important factor in modeling and describing many chemical processes, mechanical systems, teleoperation and networked control systems. On the other hand, model predictive control is a very useful and powerful tool for handling different types of systems including time delayed systems. The main disadvantage of model predictive control is massive computational load and which may lead to wasting system resources. One of the best options for dealing with this issue is to employ event-triggered strategy in model predictive control. Using this approach can relax computational efforts and save system resources. This thesis is focused on introducing a robust model predictive control using... 

Consensus is the equality of desired states of agents. These states could be position, movement direction or other variables of agents. So far, different control algorithms are introduced which provide agents with consensus. In fact, one of the most significant topics in cooperative systems is the problem of determining the control algorithm so that agents reach consensus. These algorithms are called consensus algorithms. Properties of system matrices play an important role in consensus algorithms and analysis of their convergence. In this thesis, two consensus algorithms are presented for networks with fixed and switching topology respectively. In these algorithms an input signal is... 

In this thesis, partitioning of multi inputs nonlinear dynamical systems into distinct subsystems with the goal of designing decentralized, distributed, and cooperative predictive controllers for reducing the computational load and time in practical implementations has been studied. At first, the concept of dynamical systems graph is introduced and the problem of decomposing nonlinear dynamical systems into distinct subsystems has been converted to the problem of decomposing dynamical systems graph into separate subgraphs. The proposed method for decomposition of the dynamical system graph is represented as a linear integer optimization programing where the separated subgraphs is obtained by... 

In this thesis, the general form of descriptor linear systems with time-delay is studied. First, an approach is presented to analyze the stability of descriptor linear systems with commensurate time-delay. Through this approach, not only stable and unstable regions of the system can be determined, but also the number of unstable roots in each unstable region can be calculated. Additionally, a decomposition approach is proposed, which transforms the descriptor systems with time-delay to normal time-delay systems with a lower order. As a result, a large number of methods which are only available for normal systems with time-delay can be utilized for descriptor systems with time-delay. Also,...