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Öğe Delay-dependent stability analysis of hybrid power systems with time delays(Institution of Engineering and Technology, 2016) Sezer H.; Erol H.; Ayasun S.It is essential to transmit measurements from remote terminal units (RTU) to control centre and control signals from the control centre to plant side, in load frequency control (LFC). Constant delays exist for used media in the conventional communication channels. Those delays would degrade the dynamic performance of LFC system. This paper investigates the delay-dependent stability of the LFC scheme for renewable energy power generation/storage/delivery subsystem. The investigated renewable energy power generation/storage/delivery subsystems include photovoltaic system (PV), wind turbine generator (WTG), fuel cell (FC) system and ultra-capacitor (UC) bank as energy storage system. In this paper, time delay effects of hybrid power systems are analysed by modelling the system via Matlab/Simulink.Öğe Dependency of the thermal and electrical conductivity on temperatures and compositions of Zn in the Al-Zn alloys(Taylor and Francis Ltd., 2019) Erol H.; Çadirli E.; Erol E.A.; Gündüz M.The variations of thermal conductivity (K) with temperature for Al–xZn (x = 5, 10, 20, 30, 50 and 60 wt. %) alloys were measured by using a radial heat flow furnace. The variations of electrical conductivity (?) of solid phases with temperature for the studied alloys were determined from the Wiedemann-Franz and Smith-Palmer equations by using the measured values of K from the plots of K. The thermal temperature coefficient (? TTC ) and the electrical temperature coefficient (? ETC ) were obtained. Dependency of the ? TTC and ? ETC on the composition of Zn in the Al-Zn alloys was also investigated. According to the present experimental results, K of Al–Zn alloys linearly decrease with increasing temperatures up to the melting temperature for each composition and exponentially decrease with the increasing Zn content. On the other hand, the ? of Al based Al-Zn alloys exponentially decrease with increasing temperature and Zn content. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.Öğe Effects of Growth Rates and Compositions on Dendrite Arm Spacings in Directionally Solidified Al-Zn Alloys(Springer Boston, 2017) Acer E.; Çadırlı E.; Erol H.; Kaya H.; Gündüz M.Dendritic spacing can affect microsegregation profiles and also the formation of secondary phases within interdendritic regions, which influences the mechanical properties of cast structures. To understand dendritic spacings, it is important to understand the effects of growth rate and composition on primary dendrite arm spacing (?1) and secondary dendrite arm spacing (?2). In this study, aluminum alloys with concentrations of (1, 3, and 5 wt pct) Zn were directionally solidified upwards using a Bridgman-type directional solidification apparatus under a constant temperature gradient (10.3 K/mm), resulting in a wide range of growth rates (8.3–165.0 µm/s). Microstructural parameters, ?1 and ?2 were measured and expressed as functions of growth rate and composition using a linear regression analysis method. The values of ?1 and ?2 decreased with increasing growth rates. However, the values of ?1 increased with increasing concentration of Zn in the Al-Zn alloy, but the values of ?2 decreased systematically with an increased Zn concentration. In addition, a transition from a cellular to a dendritic structure was observed at a relatively low growth rate (16.5 µm/s) in this study of binary alloys. The experimental results were compared with predictive theoretical models as well as experimental works for dendritic spacing. © 2017, The Minerals, Metals & Materials Society and ASM International.
