116 research outputs found
Structural analysis of pole assignment and stabilization in dynamic systems
Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent Univ. , 1989.Thesis (Ph.D.) -- Bilkent University, 1989.Includes bibliographical references leaves 127-132.Motivated by the need for qualitative investigation of general system
properties such as controllability, obser\^bility, existence of fixed modes,
etc. as the complement of the quantitative approach in analysis, especially
of large-scale systems, the problems of pole assignability and stabilizability
are considered from the structural point of view. The study is based on
the definition of a generic property as a property that holds for almost all
values of the nonzero system parameters. Structured matrices and digraphs
are used for system description. Both problems are first formulated in an
algebraic setting and then translated to a structural framework by means of
several graph-theoretic results which give sufficient conditions for solvability,
in terms of the existence of particular cycle families in the digraph. Following
a similar approach, a graphical investigation of structural observability is
presented. Lastly, genericity of several results are reconsidered in the light of
these graphical characterizations.Şefik, AylaPh.D
Functional target controllability of networks: structural properties and efficient algorithms
In this paper we consider the problem of controlling a limited number of
target nodes of a network. Equivalently, we can see this problem as controlling
the target variables of a structured system, where the state variables of the
system are associated to the nodes of the network. We deal with this problem
from a different point of view as compared to most recent literature. Indeed,
instead of considering controllability in the Kalman sense, that is, as the
ability to drive the target states to a desired value, we consider the stronger
requirement of driving the target variables as time functions. The latter
notion is called functional target controllability. We think that restricting
the controllability requirement to a limited set of important variables
justifies using a more accurate notion of controllability for these variables.
Remarkably, the notion of functional controllability allows formulating very
simple graphical conditions for target controllability in the spirit of the
structural approach to controllability. The functional approach enables us,
moreover, to determine the smallest set of steering nodes that need to be
actuated to ensure target controllability, where these steering nodes are
constrained to belong to a given set. We show that such a smallest set can be
found in polynomial time. We are also able to classify the possible actuated
variables in terms of their importance with respect to the functional target
controllability problem.Comment: 10 pages, 4 diagrams; to appear in the IEEE Transactions on Network
Science and Engineerin
Miniaturized Microwave Devices and Antennas for Wearable, Implantable and Wireless Applications
This thesis presents a number of microwave devices and antennas that maintain
high operational efficiency and are compact in size at the same time. One goal
of this thesis is to address several miniaturization challenges of antennas and
microwave components by using the theoretical principles of metamaterials,
Metasurface coupling resonators and stacked radiators, in combination with the
elementary antenna and transmission line theory. While innovating novel
solutions, standards and specifications of next generation wireless and
bio-medical applications were considered to ensure advancement in the
respective scientific fields. Compact reconfigurable phase-shifter and a
microwave cross-over based on negative-refractive-index transmission-line
(NRI-TL) materialist unit cells is presented. A Metasurface based wearable
sensor architecture is proposed, containing an electromagnetic band-gap (EBG)
structure backed monopole antenna for off-body communication and a fork shaped
antenna for efficient radiation towards the human body. A fully parametrized
solution for an implantable antenna is proposed using metallic coated stacked
substrate layers. Challenges and possible solutions for off-body, on-body,
through-body and across-body communication have been investigated with an aid
of computationally extensive simulations and experimental verification. Next,
miniaturization and implementation of a UWB antenna along with an analytical
model to predict the resonance is presented. Lastly, several miniaturized
rectifiers designed specifically for efficient wireless power transfer are
proposed, experimentally verified, and discussed. The study answered several
research questions of applied electromagnetic in the field of bio-medicine and
wireless communication.Comment: A thesis submitted for the degree of Ph
Graph Theoretic Analysis of Multi-Agent system Structural Properties
Ph.DDOCTOR OF PHILOSOPH
Recent progress in bio-inspired macrostructure array materials with special wettability—from surface engineering to functional applications
Bio-inspired macrostructure array (MAA, size: submillimeter to millimeter scale) materials with special wettability (MAAMs-SW) have attracted significant research attention due to their outstanding performance in many applications, including oil repellency, liquid/droplet manipulation, anti-icing, heat transfer, water collection, and oil–water separation. In this review, we focus on recent developments in the theory, design, fabrication, and application of bio-inspired MAAMs-SW. We first review the history of the basic theory of special wettability and discuss representative structures and corresponding functions of some biological surfaces, thus setting the stage for the design and fabrication of bio-inspired MAAMs-SW. We then summarize the fabrication methods of special wetting MAAs in terms of three categories: additive manufacturing, subtractive manufacturing, and formative manufacturing, as well as their diverse functional applications, providing insights into the development of these MAAMs-SW. Finally, the challenges and directions of future research on bio-inspired MAAMs-SW are briefly addressed. Worldwide efforts, progress, and breakthroughs from surface engineering to functional applications elaborated herein will promote the practical application of bio-inspired MAAMs-SW
Decentralized Power Management in Microgrids
A large number of power sources, operational in a microgrid, optimum power sharing and accordingly controlling the power sources along with scheduling loads are the biggest challenges in modern power system. In the era of smart grid, the solution is certainly not simple paralleling. Hence it is required to develop a control scheme that delivers the overall power requirements while also adhering to the power limitations of each source. As the penetration of distributed generators increase and are diversifi ed, the choice of decentralized control becomes preferable. In this work, a decentralized control framework is conceived. The primary approach is taken where a small hybrid system is investigated and decentralized control schemes were developed and subsequently tested in a hardware in the loop in conjunction with the hybrid power system setup developed at the laboratory. The control design approach is based on the energy conservation principle. However, considering the vastness of the real power network and its complexity of operation along with the growing demand of smarter grid operations, called for a revamp in the control framework design. Hence, in the later phase of this work, a novel framework is developed based on the coupled dynamical system theory, where each control node corresponds to one distributed generator connected to the microgrid. The coupling topology and coupling strengths of individual nodes are designed to be adjustable. The layer is modeled as a set of coupled differential equations of pre-assigned order. The control scheme adjusts the coupling weights so that steady state constraints are met at the system level, while allowing flexibility to explore the solution space. Additionally, the approach guarantees stable equilibria during power redistribution. The theoretical development is verified using simulations in matlab simulink environment
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