Sharif Digital Repository

Fuel cells are considered as one of the most promising for production of efficient and low-polluting electrical power. Hence, they can be a suitable alternative for fossil fuel sources. The solid oxide fuel cell (SOFC) is a direct conversion process, which works at high operating temperature (about 1000 °C). This high operating temperature makes them suitable for combining with gas turbines to achieve high overall fuel and power efficiency. A hybrid comportment consisting of an SOFC and a turbine (GT) is a multivariable nonlinear and strongly coupled system. On the other hand, total power generation in these systems which is a principal parameter should not be so sensitive to operating... 

Integrated SOFC plants, because of the high efficiency and optimum energy consumption, are important processes that have many applications. According to the importance of these plants, their optimum operability and favorable operations are also very important. One of the ways to optimize the process performance is the suitable selection of the control structures. The objective of this project is to analyze the operability or inherent controllability of integrated SOFC plants in the absence of any controller. In this work, the controllability of the process have been investigated with using the output controllability index and the other indexes such as relative gain array, singular value and... 

Molten carbonate fuel cell (MCFC) is a kind of high operating temperature fuel cells (600-800℃), tupically used for stationary power plant. These fuel cells have high efficiency (about 50%), but expensive to produce electricity. Hence, fuel cells are integrated into gas turbine cycle to decrease cost and increase efficiency of system. In this work, an integrated pressurized molten carbonate fuel cell is selected. Then, structure of selected process is changed and two new systems have proposed. Then, steady-state and dynamic behaviors of three systems were simulated separately, and their performances were compared. Efficiency increased about 5% in two new structures. Total power of system,... 

Selecting an appropriate control structure is an important subject in the design of control systems. Distillation column is one of the most popular and widely used unit operations in industry which complete understanding of its operability and controllability is one of the most important issues in the process control engineering. The present work studies the method of Output Controllability Index for nonlinear systems and compares it with Relative Gain Array and Condition Number. By using this index, the extent of intrinsic controllability of a process can be identified quantitatively in the absence of any controller. Also, the controllability of the process can be stated numerically or... 

Selection of the most appropriate control configuration for two point control strategy in a distillation column is a challenging problem. In the present work, three control configurations namely , and , have been employed to control a high purity distillation column separating the binary mixture of Benzene-Toluene. A simple linear model for the process has been derived via a system identification technique. The uncertainty and performance weights have been defined and have been utilized to design a robust controller based on the μ-synthesis approach. The genetic algorithm is employed and the peak value of μ is minimized in order to obtain appropriate PI controller parameters for each... 

In this thesis, a new method is proposed to find the class of stabilizing control structures for interconnected systems from a graphtheoretic
perspective. The objective is to classify all possible control structures (static or dynamic), capable of stabilizing the closedloop system. The method can be formulated by using the characteristics of fixed modes of the system for arbitrary control structures.To this end, first, a method is proposed based on solving a set of discrete linear programming to determine whether a system is stabilizable via a decentralized controller. Subsequently, by solving a set of discrete linear feasibility problems, all possible stabilizing controller structures... 

In this thesis, the optimal control structure selection and design of sparse multi-variable control systems is addressed. A fundamental challenge which frequently emerges in engineering, social, and economic sciences, is the optimal selection of a subset of elements, in order to maximally fulfil a design objective. In practice, it is required to solve this underlying selection problem in conjunction with a non-linear or non-convex optimization which is designed to ensure desired performance. The requirement to solve these two problems simultaneously is what makes it inherently difficult; one which has thus far eluded efforts to develop a systematic means of determining its solution. In spite... 

this work devoted to the optimal control problem for an ecosystem composed of one predator and two competing preys, and our goal is to maximize the total density of the three populations. we first investigate the existence and uniqueness of the positive strong solution for the controlled system, and find an optimal solution under given initial conditions. then we establish the first order necessary optimality condition, and point out that the optimal control has a bang-bang form. moreover, the second order necessary and sufficient optimality conditions are established  

In optimal control,local quadratic growth estimation in case of continuous control functions, and for bang–bang optimal controls when the state system is linear, has been obtained. The paper provides a generalization of the latter result to bang–bang optimal control problems for systems which are affine-linear w.r.t. the control but depend nonlinearly on the state.Local quadratic growth in terms of L1 norms of the control variation are obtained under appropriate structural and second-order sufficient optimality conditions