Browsing by Author "Akdemir, Murat"

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Design and Simulation of Active Direct Current Filter for High Voltage Direct Current Transmission Systems
(Gazi Univ, Fac Engineering Architecture, 2016) Akdemir, Murat; Yildirim, Selcuk; Genc, Naci
In this paper, firstly, a monopolar High Voltage Direct Current (HVDC) transmission system model has been formed. Series, parallel and series-parallel active direct current filter designs were carried out to suppress harmonics caused by the converters in this HVDC transmission system. Simulations of the designed HVDC transmission system using these filter were carried out in MATLAB Simulink. Waveforms and total harmonic distortion (THD) values of load current and voltage were obtained in this transmission system model for filtered and unfiltered conditions. Harmonics in the load voltage and current were suppressed to a large extent by active direct current filter used in the HVDC transmission system. Furthermore, THD values for current and voltage were obtained significantly below 5%. According to these results, designed active direct current filters which have simple structure and not complex controller offer significant advantages.
Ruthenium Modified Defatted Spent Coffee Catalysts for Supercapacitor and Methanolysis Application
(Wiley, 2021) Akdemir, Murat; Hansu, Tulin Avci; Caglar, Aykut; Kaya, Mustafa; Kivrak, Hilal Demir
Currently, a novel green material, defatted spent coffee ground (DSCG), is employed as a support to prepare DSCG supported Ru (DSCG-Ru) material. DSCG and DSCG-Ru materials are characterized by advanced surface analytical techniques such as N-2 adsorption-desorption, X-ray diffraction, X-ray photoelectron spectroscopy, and H-2-temperature-programmed reduction. Characterization results revealed that DSCG-Ru was prepared successfully. First, DSCG-Ru is prepared at varying Ru contents on deoiled coffee waste and hydrogen production experiments are performed by the methanolysis of sodium borohydride on the DSCG-Ru catalysts. It is observed that optimum conditions for the catalyst preparation are examined on the 10% Ru containing DSCG-Ru catalysts and found as 10% Ru, 300 degrees C, and 60 minutes. DSCG catalyst containing 10% Ru completed the methanolysis reaction in 1.5 minutes. Capacitive measurements to investigate the supercapacitor property of DSCG-Ru catalysts prepared at optimum conditions 10% Ru, 300 degrees C, and 60 minutes is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge measurements. Results revealed that gravimetric capacitance of the electrode at a current density is found as of 0.5 A/g and 43 F/g, greater than the literature values. DSCG-Ru, green novel supported Ru catalyst, has a dual promising performance in hydrogen production and supercapacitor measurements.
Yüksek Gerilimli Doğru Akım İletim Sistemleri için Aktif Doğru Akım Filtresi Tasarımı ve Simülasyonu
(2016) Akdemir, Murat; Yıldırım, Selçuk; Genç, Naci
Bu çalışmada, ilk önce tek kutuplu bir Yüksek Gerilimli Doğru Akım (YGDA) iletim sistemi modeli oluşturulmuştur. Bu YGDA iletim sisteminde dönüştürücülerden kaynaklanan harmonikleri bastırmak için seri, paralel ve seri-paralel aktif doğru akım filtre tasarımları gerçekleştirilmiştir. Tasarlanan bu filtrelerin kullanıldığı YGDA iletim sisteminin simülasyonları MATLAB Simulink'te gerçekleştirilmiştir. Bu iletim sistemi modelinde filtresiz ve filtreli durumlar için yük akımının ve geriliminin dalga şekilleri ile toplam harmonik distorsiyonu (THD) değerleri elde edilmiştir. YGDA iletim sisteminde kullanılan aktif doğru akım filtreleriyle yük gerilimindeki ve akımındaki harmonikler büyük oranda bastırılmıştır. Ayrıca bu akım ve gerilimler için THD değerleri %5'in oldukça altında elde edilmiştir. Bu sonuçlara göre, tasarlanan aktif doğru akım filtrelerinin basit bir yapıya sahip olması ve kontrolünün fazla karmaşık olmaması önemli avantajlar sağlamaktadır.