Sharif Digital Repository

Arc welding is one of the key processes in the industry. Its vocational status in manufacturing industry comes to third place. From applicable standpoint gas metal arc welding (GMAW) has especial place between various electrode arcs. Base on the mode of transferring welding drop from electrode into welding pool the GMAW process could be categorized. The physics of metal transfer is not yet well understood, due to the facts that the arcs area is too small, the temperatures is too high and the metal transferring is at too high rate. However, physical behavior of process of each model is different from another. So equations that express each of them, need to reform toward others. The conditions... 

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... 

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... 

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... 

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... 

In this project a complete simulator for a two-winding, 25cm air gap Maglev system by considering the pratical constaritns, position and velocity observer and the current sensor dynamics was derived. In order to control the ball in any desired position a twisting sliding mode controller was designed as the basic controller in the rest of project. The designed controller can not transfer the ball in far trajectory. In first step we modify that to reach a better performance by changing the value of current, passing through the coils in steady state. In the second step, the far trajectories are divided to a finite number of sub-trajectory such that the ball can pass these sub-trajectory by... 

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... 

Inthis thesis, we provide a reduced multiple linear approximationfornonlinear systems. This approximationis a weighted summation of reduced order models thatapproximates the states or output(s) of the nonlinear system. It can be used inreal-time control instead of high-ordernonlinear models in order toreduce thecomputational cost. The reduction of computation cost is claimed qualitatively, based on the linearity of the approximation and its less order compared to the original model. To form amultiple modelapproximation eachlinearmodelis obtained from linearization atanoperating point. Then,each model is reduced byalinearreduction method. We used truncation and balanced residualization... 

The focus of this thesis is on robust control of hybrid systems using tube-based model predictive control. Hybrid systems are systems that contain both continuous and discrete components. The hybrid nature of these systems can stem from inherent switching behavior that occurs in many dynamical or digitally controlled systems, or from approximation of nonlinear systems. The ability of these systems to model a vast amount of physical phenomena has been attracted a lot of attention from control society. Although much effort have been made on the control of “nominal” hybrid systems, robust stabilization of these systems still seems to be immature. One of the most successful approaches toward... 

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... 

In today's world we are dealing with many devices and processes with the goal of efficiency and performance improvement. In many processes particularly chemical ones, the goal is to control the output according to its constraints in the way that the performance is economically efficient, such as reducing energy consumption and energy loss and increasing efficiency. In order to control a process with economical goals, an economical cost function is used and after determination of optimal values a controller is used to guide the process so can achieve them. Model predictive control (MPC) is very common in this economic control Due to advantages such as considering the problem constraints. In... 

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... 

A control system capable of tolerating system malfunctions while maintaining an acceptable level of performance is referred as fault tolerant control system. The constraints on the amplitude of input control signals limit the domain of attraction even for linear models. Ignoring this fact may lead to an unsatisfactory performance and even closed loop instability. Designing the controller such that the domain of attraction is maximized has been an attractive topic for researchers. On the other hand, persistent disturbances always play an essential role in the real word systems. Designing the controller in a way such that the effect of such disturbances is attenuated is another challenging... 

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,... 

In this paper, an approach is proposed to estimate the location of the leaks in oil pipelines. The pipeline possesses a system of Partial Differential Equations (PDE). First, a closed-form solution is applied to the pipeline equations and the leakage location is found solving the steady-state equations. To tackle the case where the pressure and flowrate do not reach constant values, the initial estimations are provided by the closed-form solution. Then, the pressures, flow rates, and leakage coefficient are estimated by solving the system of differential equations. This system is then discretized with respect to the location variable to yield the system state equations which, in turn, are... 

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... 

Many processes and real world systems indicate nonlinear behavior and operate either naturally in multiple regions or in a wide range of operation space. Modelling and control of these systems by nonlinear methods needs to have a deep insight. Furthermore, the nonlinear methods leads to complexity issues. To overcome these problems, multi-model methods are introduced which consist of two steps, decomposition and combination. In decomposition step, the complex system is divided into a set of simple models; in the combination step, the behavior of local models are combined. How to decompose to local models and how to combine them are two main questions in this area which not answered... 

In recent decays, multiple model controllers have been attracted much attention due to their essential ability to control of non-linear systems with wide operating ranges. Number and location of models are two important factors. In this research an algorithm for determining number of models and their locations has been proposed which can be counted as an extension to existing algorithms. Utilizing the proposed algorithm, the minimum number of models which achieve closed-loop stability can be determined. If transient response of non-linear system with these models be not satisfactory, the number of models are increased by one using Binary Search method, and consequently the location of models... 

This thesis is concerned with the robust control of multiple integrator systems, subjected to input saturation and external disturbance. Since nested saturation method has been demonstrated to be an effective tool for control of a chain of integrators, a feedback law using nested saturation is proposed. In order to deal with disturbance, an extended state observer is applied to nested saturation controller and a comprehensive analysis of stability is also presented. The existence of constant parameters in the proposed controller makes the design conservative which results in performance degradation in some cases at the presence of disturbance. To overcome this issue, an adaptive approach...