FBE- Elektrik Mühendisliği Lisansüstü Programı - Yüksek Lisans
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Sustainable Development Goal "none" ile FBE- Elektrik Mühendisliği Lisansüstü Programı - Yüksek Lisans'a göz atma
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ÖgeElektrikli araçlar için asenkron makinelerde rotor oluk geometrilerinin uzay harmonik ve işletme başarımı üzerine etkilerinin tespitine katkılar(Fen Bilimleri Enstitüsü, 2019-06-14) Lordoğlu, Abdulsamed ; Kocabaş, Derya Ahmet ; 504161051 ; Elektrik MühendisliğiKüresel ısınma, çevre kirliliği, fosil yakıtların tükenmesi gibi problemler çevreye olan bilinci ve nihayetinde onu korumaya ve zarar vermemeye yönelik çalışmaları arttırmıştır. Elektrikli araçların gelişiminde rol oynayan bu etkenler ile birlikte günümüzde yapılan çalışmalar da elektrikli araç teknolojisini gittikçe geliştirmektedir. Elektrikli araç teknolojisine olan eğilime paralel olarak elektrik tahrik sistemlerinin gelişimine yönelik çalışmalar da artmaktadır. Elektrikli araçlarda tahrik motoru olarak çeşitli motorlar kullanılmaktadır. Bunlar genelde asenkron motor, sürekli mıknatıslı senkron motor, anahtarlamalı relüktans motor, geleneksel doğru akım motoru ve senkron relüktans motordur. Bu motorların birbirlerine göre çeşitli avantaj ve dezavantajları bulunmaktadır. Asenkron motorlar düşük maliyetleri, basit ve sağlam yapıları, yüksek verimleri, düşük titreşime/gürültüye sahip olmaları gibi özelliklerinden dolayı elektrikli araç uygulamalarında tercih edilmektedirler. Geçmişten günümüze kadar çeşitli elektrikli araç uygulamaları yapılmıştır. Bu araçlardan Tesla Model S, BMW X5, Ford Focus EV ve Tesla Roadster gibi öne çıkan marka ve araçlar tahrik motoru olarak asenkron motor kullanmayı tercih etmişlerdir. Elektrikli araç uygulamalarında kullanılan elektrik motorunun işletme başarımını arttırmak ve maliyetini azaltmak amacıyla çeşitli çalışmalar yapılmaktadır. Bu çalışmada elektrikli araçlar için tasarlanmış sincap kafesli asenkron motorda rotor oluk geometrilerinin motorun işletme başarımı, kalkış performansı, verimlilik, titreşim ve akustik gürültü gibi kriterlere etkisi incelenmiştir. Elektrikli araçlarda kullanılan motorların yüksek moment/güç yoğunluğu, düşük titreşim/gürültü, ani hızlanma/yavaşlama, düşük maliyet/ağırlık, geniş hız aralığı ve "tüm hızlarda yüksek verim" gibi özelliklere sahip olması gerekir. Bu tasarım isterleri göz önüne alınarak tasarlanacak motor için bir verim hedeflenmiş ve motor gücü, kutup sayısı, stator ve rotor oluk sayıları, hız aralıkları gibi motor değerleri pratikte kullanılan makine özelliklerinden yola çıkılarak belirlenmiştir. Belirlenen bu değerlere göre geleneksel analitik yöntemler ile makine başlangıç fiziki boyutları hesaplanmıştır. Makinede kullanılacak manyetik malzemenin doymaması ve buna bağlı olarak manyetik kayıpların oluşmaması ve nihayetinde makine veriminin yüksek olması amacıyla makinenin çeşitli bölümlerinde standartlar ve genel tasarım ilkeleri dikkate alınarak manyetik kısıtlar belirlenmiştir. Geleneksel yöntemler ile hesaplanan makinenin fiziki boyutlarında, manyetik kısıtlar göz önüne alınarak bilgisayar destekli analiz ile iyileştirme yapılmış ve nihai boyutlar belirlenmiştir. NEMA, IEC gibi motor standartları ve literatürde yapılan çalışmalar değerlendirilerek asenkron motorlarda kullanılan rotor oluk şekillerine yeni ve özgün oluk tasarımları da eklenerek belirli bir sınıflandırma altında farklı rotor oluklarına sahip 13 motor tasarlanmıştır. Stator demir çekirdeği sargısı ve oluk şekli 13 tasarım için değiştirilmemiş olup 2 tabakalı sargı, sabit diş genişliği ve yamuk kesitli oluk kullanılmıştır. Makine ana boyutları ve stator yapısı değişmemek kaydıyla tasarlanan her bir motor için rotor oluk şekline ait boyutlar değiştirilerek en uygunlaştırma yapılmıştır. İlgili rotor oluk geometrik boyutlarının en uygunlaştırılması için ANSYS Electronic Desktop kullanılmış ve analiz kriteri olarak en yüksek verim alınmıştır. Bu en uygunlaştırma oluk geometrisinin karmaşıklığına bağlı olup karmaşık geometriler için daha fazla analiz yapmak gerekmiştir. Tasarlanan farklı rotor oluk geometrilerine sahip 13 motor, bilgisayar destekli sonlu elemanlar yöntemi ile sabit moment kriteri altında incelenmiş ve geçici hal analizine tabi tutulmuştur. Bu motorların elektriksel, manyetik, harmonik ve gürültü yönünden işletme başarımları elde edilmiş ve karşılaştırılmıştır. Bilgisayar destekli analiz programları ile her bir rotor oluk çeşidi için makinelerin hava aralığındaki manyetik akı yoğunluğunun radyal bileşeni açısal konuma bağlı olarak elde edilmiş ve Fourier Analizi ile harmonik spektrumları elde edilmiştir. Harmonik dağılımdan faydalanarak makine üzerinde en büyük bozucu etkisi olan uzay harmoniklerine yoğunlaşılmış ve bu harmonik derecelerinin kısıtı altında motorlar en küçük harmonik içeriğinden en büyük harmonik içeriğine doğru sıralanmıştır. Uzay harmoniklerinin akustik etkisini inceleyebilmek adına seçilen oluk tipleri üzerine yoğunlaşılmıştır. Bu amaçla en büyük harmonik içeriğe, en küçük harmonik içeriğe ve "kalkış akımı, kalkış momenti, verim, harmonik içeriği, moment titreşimi" dikkate alınarak seçilen en uygun işletme başarımına sahip 3 oluk tipi üzerine yoğunlaşılmıştır. Seçilen 3 oluk tipine ilişkin analiz sonuçları ANSYS Workbench programına aktarılarak uzay harmoniklerinin etkisi sonucu oluşan manyetik akustik gürültüler incelenmiştir. Bu yolla makinelerin manyetik yolla oluşan akustik gürültü seviyeleri ve değişimleri karşılaştırılmıştır. Bu tez ile standart elektrik makinesinin tasarımı ve sayısal yöntemle incelemesi çalışmalarına ilave olarak uzay harmoniklerinin mekanik ve akustik etkileri incelenmiş ve 13 farklı oluk tipinin seçilen kriterler altında başarımları elde edilmiştir. Elektrikli araçlar için özel olarak tasarlanacak elektrik motorlarında rotor oluk tipinin kolayca belirlenebilmesi için sonuçlar karşılaştırmalı olarak verilmiştir.
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ÖgeFlexible load management in active distribution system(Institute of Science and Technology, 2020) Parchehbaf Dibazari, Shahram ; Türkay, Belgin ; 637477 ; Elektrik MühendisliğiPower networks have been developing since they appeared, and this development has accelerated because of developed technology. Along with the changing living conditions, the amount of electricity consumed in the networks has increased regularly every year. On the other hand, industrialization has caused the more big-amount loads to be added to the network, especially industrialization has been a major factor in the increase of electricity demand of developing countries such as southeast Asia and in this direction, their increase in electricity generation capacities or towards them to the import of electricity. As a result of these changes and developments in the networks, the power systems have grown over time and interconnected or wide area synchronous networks have emerged. Sometimes these networks have emerged as sub-networks of a national network, and sometimes by connecting the national networks of different countries. Interconnected networks were created in order to meet the consumption in the network more comfortably, especially in networks where power plants and load weights are distant, in order to carry the generated power to other regions more easily. Moreover, another reason for the emergence of these networks was to increase network stability, security, and reliability. In fact, some international interconnected grids were also helped to improve the operating standards and monitoring mechanisms of some of the countries they include, since the main principle of these networks is that they are fully synchronous in some factors such as frequency. As a result of the synchronous drift that would occur for any reason in the existing sub-networks of the interconnected network, the sub-network is disconnected and immediately separated from the interconnected network. Failure of disconnection or late separation of the network that has synchronous slippage may drag the entire network to a collapse. In addition to the increase in electricity consumption, the nature of the network and type of elements such as load and generators have changed in recent years. Moreover, the inclusion of renewable and distribution generators, which are producing on a small scale, the fact that some loads enter and exit to the network rapidly, and the emergence of a fact like electricity market, in spite of the benefits they add to the network, can be caused some problems if not properly managed. For instance, there are some issues that should be managed well in the electricity market such as taking the offers for the next day and make the necessary preparations by making the day ahead load forecast very carefully. Furthermore, some power plants refrain from bidding for economic reasons, or they may prefer to stay out of the market by placing higher bids, so that the control authority must impose necessary preventive practices in this regard in order to avoid generation deficiencies. It is very important to schedule a planned maintenance in power plants, also small generation sources should be evaluated and planned very well. Even if the market conditions of the day before have been well evaluated, it is inevitable that some problems in the network will still be experienced. These problems may be encountered when the generation and consumption capacity balance is on the border, or when the reserves do not meet the total consumption. The balance of generation and consumption should always be equal in the network, that is, generation or consumption should not be less or more than one another, so the network operator tries to keep the frequency and voltage values in the network within the acceptable range by observing the balance between generation and consumption at any time. In case of severe disturbances in the network, there is a loss of generation generally, which starts to change the frequency and voltage value in the network. In this case, the network operator needs to drop the excess load to ensure balance, this operation is called Load Shedding (LS). Load shedding is generally divided into Under-Frequency Load Shedding (UFLS) and Under-Voltage Load Shedding (UVLS). The difference between these methods is the load shedding is performed by observing the frequency value in one and the load shedding done by observing the voltage value in the other. Conventional methods are available for both load shedding, these conventional methods often attempt to balance the network by removing the load in predetermined steps. These methods are generally decentralized, that is, they do not provide a specific solution for every situation, but they go towards reducing the load in certain buses and at certain levels. Of course, this situation can sometimes lead to under-shedding or an over-shedding of the desired amount, which in turn causes the network to collapse. In addition to the amount of load to be thrown, the time to apply the load shedding is also very important. If the operation is not carried out in time, the network goes to the collapse again and the load to be thrown is not important anymore. The buses where the load shedding is to be applied is another important aspect so that when conventional load shedding methods cannot produce a solution to the situation, they apply the load shedding process at the previously determined buses. In developing power networks, developing new methods for load shedding is at the forefront of experts for a long time. Almost all of the newly developed methods are centralized and they have the ability to generate solutions by observing all the buses in their own responsibility areas and collecting data, evaluating the status of the network in case of problems by using the communication infrastructures. When the grid condition is evaluated and processed with the help of computers, the amount of load, time and place to be thrown can be selected and applied more accurately. These methods proposed in recent years due to increase in the amount of data, limited response time, and most importantly, to achieve the best answer are generally developed with supporting of optimization algorithms. The performance and usability of optimization algorithms in power systems can be clearly seen in other studies topics such as protection systems. In this thesis, flexible load management optimization by using load shedding and optimal reconfiguration in active distribution power networks were studied. Hence, in the first chapter of this thesis, the development, structure, basic concepts, network values which were taken from different countries, and consumption data with real data were shown and compared. Furthermore, information and evaluations about previous studies and the purpose of the thesis were included in this chapter. In the second chapter, voltage stability, voltage collapse, load shedding definition, and classifications were discussed. In the third chapter, the amount, location and timing of load shedding, load shedding, and power flow formulations were discussed. Also, the definition of various optimization algorithms like Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and Binary Particle Swarm Optimization (BPSO) were discussed. Finally, an explanation about Optimal Distribution Network Reconfiguration (ODNR), also explanation and formulation of voltage stability index which was used in the second study case are also available. In the fourth chapter, for the first study case, simulation and results of the applied method were given. At this stage, after evaluating a 69-bus and 33-bus IEEE distribution test system under normal conditions, the system was self-healing with optimal switching with the help of the BPSO optimization algorithm, and the results were shared. Then, the BPSO optimal switching and load shedding through the power flow process were performed together, and the results were given for each evaluated in three cases. A novel method was proposed in the second study case. In this study case, in the 33-bus IEEE distribution test system, a smart grid was considered. load management was carried out with controllable loads in smart homes by load shedding with the help of the PSO optimization algorithm. The results of this newly proposed method were given for two different analysis cases. In the last chapter, conclusions and recommendations regarding both study cases of the thesis were presented in the fifth chapter.
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ÖgeInvestigation of timbral qualities of guitar using wavelet analysis(Institute of Science and Technology, 2020) Ekmen, Şafak ; Şeker, Şahin Serhat ; Karadoğan, Can ; 637532 ; Electrical Engineering DepartmentThis study presents a practical and accurate technique using the power of wavelet analysis for investigating timbral qualities of classical guitars. Work includes complete work frame from the experimental procedure through capturing the data with piezoelectric film sensors, which have not been widely applied for this type of application, to the analysis of captured information. Aim is to present a study for more objective evaluation of guitars that is suitable for performing by the different parties of the field; from instrument makers and designers to the quality control engineers and end users. It is believed that with the right improvements and modifications, system presented in this thesis can be used for detailed cataloging of different guitars and their timbral characteristics, which in turn can be used in range of areas such as music information retrieval, guitar research and development and probably even for genuity testing of the guitars. Structure of this study as follows: first understanding the concept that is being investigated, timbre is explored after the introduction. Properties of timbre and the studies that discovered these properties are reviewed. In the following chapter, wavelet theory, which is the backbone and most important aspect of this study is explained in a level that provides intuitive grasping of the concept, because the area is vast and ever improving. Then subject of the study that is guitar is presented through the studies of guitar analysis literature. Then, naturally comes the chapter that the experimental setup and procedure is explained as well as performed analysis and its results are presented with their interpretation and comments. Finally, conclusion of the study with a discussion is given. Experiments was performed in the main studio of Istanbul Technical University/Center for Advance Studies in Music. A mass produced guitar that is described as a learning guitar by its production company and a luthier-made guitar were used. Procedure is done while a guitar player holding the guitar in a conventional playing position and plucking the strings with a pluck. A minor diatonic scale with addition of A minor chord at the end, both in open position and 5th position is played. Choice of the played scale was rather arbitrary whereas the choice of playing the scale in two position on the fingerboard is made to observe the effect of excitation epicenter on the finger board. Piezofilm sensors was used because of their wide frequency range, near-flat frequency response and low mass. Analysis were performed in MATLAB environment using Wavelet Toolbox. First Continuous Wavelet Transform is applied. Continuous Wavelet Transform is a highly computation heavy method for general applicability and the resolution of the results can be far more detailed than necessary for some applications in the area. For this reason, Wavelet Packet Transform is performed to present a more computationally inexpensive solution that provides adequate detail. Results show detailed presentation of harmonic and non-harmonic partials as well as time envelopes of them in a resolution that cannot be obtainable using Short Time Fourier Transform. Resolution of the results allow for objective analysis on the timbre of a guitar as well as making comparison between the timbral properties of the two guitars.