Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411
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Article Citation - WoS: 4Citation - Scopus: 6Case Study on Thermal Optimization of Oil Immersed Transformer Used in Solar Power Plant Based on Genetic Algorithm and Computational Fluid Dynamics(Vinca inst Nuclear Sci, 2023) Iskender, Ires; Yukselen, EmirTransformers are one of the most capital investments in the solar power generation. Their safe and stable operations in the electrical networks are important. The main failure factor of transformers is the high temperature generated by the losses during operation, which increases the probability of insulation damage that significantly affects the useful life of transformer. Considering the importance of oil temperature and its effects on the life of the transformer, a numerical method is developed in this paper to optimize the cooling system of the transformer. In this regard, genetic algorithm is used as an optimization method to minimize the total cost of the cooling system while maintaining the required thermal conditions of the transformer. A comprehensive parametric study is carried out among the effective cooling geometry parameters using 3-D electromagnetic and thermal models of the photovoltaic transformer to evaluate and analyze the temperature distribution. The accuracy and feasibility of the proposed method is established by comparing the numerical results with those obtained from the experimental test. The results of the proposed method are found to be in a good agreement with the experimental and simulation results.Article Antenna Synthesis by Levin's Method Using Reproducing Kernel Functions(Applied Computational Electromagnetics Soc, 2023) Sener, GokerAn antenna synthesis application is presented by solving a highly oscillatory Fourier integral using a stable and accurate Levin's algorithm. In antenna synthesis, the current distribution is obtained by the inverse Fourier integral of the antenna radiation pattern. Since this integral is highly oscillatory, the Levin method can be used for its solution. However, when the number of nodes or the frequency increases, the Levin method becomes unstable and ineffective due to the large condition number of the interpolation matrix. Thus, an improved scheme of the method is used in an antenna synthesis application in which reproducing kernel functions are used as the basis of the approximation function. The accuracy of the new method is verified by a log-periodic antenna example. The error and stability analysis results show that the new method is more stable and accurate than other well-known kernels, especially for a large number of nodes.Article Üç Fazlı Kuru Tip Transformatör Verimliliği İçin Meta Sezgisel Algoritma Tabanlı Yaklaşımlar(2021) İskender, İres; Kül, Seda; Celtek, Seyit AlperenTransformatörler, elektrik enerjisinin verimli iletimi ve dağıtımına önemli katkı sağlayan unsurlar olarak kabul edilir. Gerilim ve akım seviyelerini ters orantılı olarak değiştirme yeteneği, iletken kayıplarının azaltılmasına yardımcı olur. Bununla birlikte, günümüzün daha önemli verimlilik işaretlerine yönelik katı gereksinimleri, bir güç sistemindeki bireysel bileşenlerin verimliliğine dikkat çekiyor. Bu nedenle, temel işlevlerinden ödün vermeden transformatörlerin verimliliğini en üst düzeye çıkarmak için büyük çaba sarf edilmektedir. Bu karmaşık bir sorundur ve gelişmiş tasarım araçlarının kullanılmasını gerektirir. Son yıllarda geliştirilen meta-sezgisel yöntemler, tasarım süresinde tasarruf ve optimum çözümü bulmada büyük başarı sağladıklarından elektrik mühendisliğinde kullanılmaktadır. Bu çalışmada sırasıyla Parçacık Sürü Optimizasyonu (PSO), Benzetimli Tavlama (SA) ve Ağaç Tohum Algoritması (TSA) yöntemlerini kullandık. Amaç, üç fazlı kuru tip transformatörler için bir tasarım metodolojisi geliştirmek ve verimliliklerini en üst düzeye çıkarmaktır. Üç algoritmanın sonuçları, optimum çözümü doğrulamak için karşılaştırılır. Prosessin gösterimi için üç fazlı 100 kVA kuru tip bir transformatör kullanılır. Transformatörün matematiksel modeli oluşturulduktan sonra transformatör parametreleri, akım yoğunluğu (s) ve transformatör demir kesiti kabul edilebilirliği (C) optimize edilmiştir. Sonuç olarak, transformatörlerin verimlerinin geleneksel tekniklerle elde edilenin üzerinde artırılabileceği gözlemlenmiştir. Verimlilik optimize edilmiş ve 0.975'ten 0.9844'e yükseltilmiştir.Article Citation - WoS: 1Citation - Scopus: 1Antenna Synthesis by Levin's Method Using a Novel Optimization Algorithm for Knot Placement(Applied Computational Electromagnetics Soc, 2023) Sener, Goker- Antenna synthesis refers to determining the antenna current distribution by evaluating the inverse Fourier integral of its radiation pattern. Since this inte-gral is highly oscillatory, Levin's method can be used for the solution, providing high accuracy. In Levin's method, the integration domain is divided into equally spaced sub-intervals, and the integrals are solved by transfer-ring them into differential equations. This article uses a new optimization algorithm to determine the location of these interval points (knots) to improve the method's accuracy. Two different antenna design examples are pre-sented to validate the accuracy and efficiency of the pro-posed method for antenna synthesis applications.Article Citation - Scopus: 9Improvement of Underlay Cooperative Cognitive Networks Bandwidth Efficiency Under Interference and Power Constraints(Ksii-kor Soc internet information, 2019) Preveze, Barbaros; Alkhayyat, Ahmed; Al-Mishmish, Hameed R. M.The definition of the bandwidth efficiency (BE) of cognitive cooperative network (CCN) is the ratio between a number of the licensed slot(s) or sub-channel(s) used by the unlicensed users to transmit a single data packet from the unlicensed transmitter to unlicensed destination, and from unlicensed relay(s) to unlicensed destination. This paper analyzes and improves the BE in the underlay CCN with a new reactive relay selection under interference and power constraints. In other words, this paper studies how unlicensed cooperative users use the licensed network slot(s) or sub-channel(s) efficiently. To this end, a reactive relay selection method named as Relay Automatic Repeat Request (RARQ) is proposed and utilized with a CCN under interference and power constraints. It is shown that the BE of CCN is higher than that of cooperative transmission (CT) due to the interference and power constraint. Furthermore, the BE of CCN is affected by the distance of the interference links which are between the unlicensed transmitter to the licensed destination and unlicensed relay to the licensed destination. In addition, the BE for multiple relays selection over a CCN under interference and power constraints is also analyzed and studied, and it is shown that the BE of CCN decreases as the number of relays increases.