Elektrik- Elektronik Mühendisliği

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Browsing Elektrik- Elektronik Mühendisliği by Subject "Algorithms."

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    Convergence rate analysis and optimization of distributed consensus algorithms
    (Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2014., 2014.) Cihan, Onur.; Akar, Mehmet.
    The problem of achieving a common value in a distributed information sharing context, referred to as distributed consensus or agreement, is an important topic that has drawn significant research attention of late. Consensus algorithms find applications in many areas including network clock synchronization, sensor fusion and load balancing where achieving consensus as fast as possible is important. In this dissertation, we study the analysis and optimization of convergence rate of averaging based distributed consensus algorithms evolving on graphs. By relating the convergence speed of the algorithm to the mixing rate of a Markov chain, we propose two semi–definite programming (SDP) methods of assigning transition probabilities to a Markov chain in order to optimize its mixing rate. In the first SDP formulation, there is a single transition probability parameter to be optimized (the holding probability of vertices) which leads to easier and faster computation as opposed to the more general reversible Markov chain formulation corresponding to a stationary distribution that is proportional to the degree of vertices. By deriving exact analytical results, it is shown that both the single parameter and the degree proportional reversible fastest mixing Markov chain formulations yield better results than the symmetric SDP formulation for a path and some well–known edge–transitive and orbit graphs. The convergence rate of the averaging based distributed consensus algorithm is also analyzed for networks where delay exists in data receptions, which is unavoidable in practice. After introducing the delayed version of the consensus algorithm, it is analytically shown that bounded non–uniform delay does not adversely affect its convergence rate for directed acyclic graphs.
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    Low power Advanced Encryption Standard (AES) implementation robust against side channel attacks
    (Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022., 2022) Unal, Serdar.; Başkaya, Faik.
    As the people around the globe become increasingly connected to each other, the amount of information that flows becomes huge. Unfortunately, this vast information network is vulnerable to harmful attacks. Encryption is a strong tool that has been used for ages to act as a shield against these attacks. Among many algorithms utilized for encryption, one of the most popular is AES. AES is an approximately 20-year old algorithm that has been adopted by many organizations around the world to protect classified and unclassified data. In line with the trend of low power and secure implementations, the main intent of this thesis is to show a low-power AES implementation that is secure against power side-channel attacks. In the RTL, currently unused registers are kept constant to lower the power consumption. Choosing the LP ASIC process, using clock-gating, and preferring standard cells with higher threshold voltages enable more power saving. For the side-channel attack resistance, obfuscating and pipelining are employed. The obfuscating disguises the relation between the processed bits and the power consumption by modifying the processed information. On the other hand, the pipelining mixes power consumption related to different inputs with each other. The different versions of AES implementations are processed through FPGA and TSMC 65 nm ASIC flow to compare with each other. After the power traces are collected and analyzed by ChipWhisperer the side-channel attack resistance is evaluated. The effects of the obfuscating and pipelining in increasing attack resistance are proven after predicting key bytes from power traces stemming from thousands of random inputs. The area, power overheads in return for increased attack resistance are detected.
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    Model algorithmic control: |an application to DC motor speed control
    (Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1985., 1985.) Özperk, Tuna.; Kaynak, Okyay,
    The growth of digital technology in the last few years has represented a challenge to automatic control research workers. The increasing use of digital minicomputers has considerably helped the industrial implementation of algorithmic types of control. For this type of control to be practical and efficient,it is imperative for the controller to have access to fast digital computing facilities with fast memory access and substential information storage capacity. In this thesis a new method of digital process control which is applied 'to a number of industrial processes ranging from power plants to glass furnaces,is described.This new control method is called Model Algorithmic Control or equivalently Model Predictive Heuristic Control.A mathematical framework for the analysis of Model Algorithmic Control is developed and the operations of the main components of the control structure are described. The Model. Algorithmic Control strategy relies on three principles: i. the plant is represented by its impuls response which will be used on-line by the computer for prediction, ii.the behavior of the closed-loop system is prescribed by means of reference trajectory initiated on the actual output, iii. the control variables are computed in a heuristic way. Future inputs are computed in such a way that when applied to the internal predictive model,it induces outputs as close as possible to the desired reference trajectory. In this thesis,the Model Algorithmic Control is applied to dc motor speed control. Control algorithm is evaluated by a Z-80 based microcomputer, and the output of microcomputer is applied to a fully controlled thyristor converter unit as a speed reference input through a digital to analog converter. The actual speed of the motor is inputed to the microcomputer by means of a tachogenerator through an analog to digital converter. The application of Model Algorithmic Control to dc motor speed control is devided in two parts.In the first part of the application, the set speed is constant, the algorithm causes the speed of the motor to reach that constant speed with a time constant similar to the reference trajectory. The time responses of motor output speed are observed for different time constants.In the second part, the set speed is time varying. In this part the set speed is changed as a linear ramp,the tracking behavior of the dc motor output speed is observed. In chapter one, the methods for the speed control of a separately excited direct current motor are described and compared with each others. Consequently,the equations determining the dynamical behavior of the motor and the transfer function of the motor are derived. In chapter two, solid state dc motor drives are described and the operation of a three phase full converter is explained in general terms.The features of the thyristor unit used in the realization of the control is then presented. In chapter three, a mathematical framework for the analysis of Model Algorithmic Control is developed and. the operations of the main components of the control structure are described. The equations to calculate the optimum inputs are derived. In chapter four, the model which will be used in the algorithm is introduced. The discrete impuls response of the system is found and the overall set up for closed-loop control is given.Additionally the software developed is presented and explained. In chapter five, the stability analysis of the Model Algorithmic Controlis developed. The robustness of the system to the parameter changes is discussed.Finally the effects of the constraints on input sequence to system stability are discussed, and the experimental results are presented.
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    Model-based and model-free control algorithms for textile processes
    (Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022., 2022) Çom, Mustafa.; Akar, Mehmet.
    Textile processes consist of several control loops that require accurate reference tracking. One of the most crucial control loops is the temperature control where the temperature of the corresponding medium must track the reference value with sufficient accuracy to obtain a high-quality textile product. Even though several studies can be found on designing control algorithms for industrial processes in the literature, none of them focus particularly on the aforementioned textile processes. In this study, in order to achieve successful control, several adaptive control algorithms are developed. In addition, corresponding processes are modelled, and a simulation environment is built to increase the speed and safety of development works. Modelling is realized by dividing the corresponding process into several regions of operation, preparing sub-models for each region and building a composite model by combining these sub-models. A simulation environment is created by examining currently used control algorithms and process dynamics. The simulations of designed models result in significant accuracies. A model-based control algorithm, based on the Model Predictive Control (MPC) approach that utilises previously designed pro cess models, is developed and verified in the simulation environment. Two model-free control algorithms, referred to as Adaptive PI Control and Error Predictive Control (EPC), are developed and verified not only in the simulation environment but also in the field.