Yazar "Eminoglu, Ulas" seçeneğine göre listele

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    A Comprehensive Review and Adequacy Evaluation of Voltage Stability Indices for Modern Distribution Systems
    (PRAISE WORTHY PRIZE SRL, 2010) Eminoglu, Ulas; Hocaoglu, M. Hakan; Ayasun, Saffet
    It is well known that the network variables and parameters contain sufficient information to obtain the most sensitive bus or line to the voltage collapse in power systems. Accordingly, there has been several static voltage stability indices developed for identifying the buses or lines on the verge of voltage collapse in the literature. In this paper, various voltage stability indices including those originally developed for transmission systems are first reviewed. Then, their adequacies are quantitatively evaluated on a modern distribution test system which has voltage controlled bus (PV-bus). From analyses, it is observed that most of the existing voltage stability indices would be inadequate for assessing the most sensitive bus or line on the verge of voltage collapse in such modern distribution systems. Copyright (c) 2010 Praise Worthy Prize S.r.l. - All rights reserved.
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    A comprehensive review and adequacy evaluation of voltage stability indices for modern distribution systems
    (Praise Worthy Prize S.r.l, 2010) Eminoglu, Ulas; Hocaoglu, M. Hakan; Ayasun, Saffet
    It is well known that the network variables and parameters contain sufficient information to obtain the most sensitive bus or line to the voltage collapse in power systems. Accordingly, there has been several static voltage stability indices developed for identifying the buses or lines on the verge of voltage collapse in the literature. In this paper, various voltage stability indices including those originally developed for transmission systems are first reviewed. Then, their adequacies are quantitatively evaluated on a modern distribution test system which has voltage controlled bus (PV-bus). From analyses, it is observed that most of the existing voltage stability indices would be inadequate for assessing the most sensitive bus or line on the verge of voltage collapse in such modern distribution systems. © 2010 Praise Worthy Prize S.r.l. - All rights reserved.
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    A New Model for Output Power Calculation of Variable-Speed Wind Turbine Systems
    (IEEE, 2015) Eminoglu, Ulas; Ertan, HB
    The evolution of power semiconductors has contributed enormously to variable-speed wind turbine systems (WTS). In this study, a new method for power output calculation of variable-speed WTSs is proposed. The model is developed from the charging voltage equation of capacitors and is only a function of the rated power and the rated wind speed. It is validated on the manufacturer power curve of different type and size of variable-speed WTSs. Additionally, by using developed model, the capacity factor of this type of WTS is also modelled in terms of the rated wind speed and Weibull distribution of the wind site. Parametrical analyses have been carried out to show the effect of rated wind speed on the value of turbine capacity factor, resulting of energy production for different wind conditions (Weibull scale parameter). The feasible value of rated wind speed for located or considered variable-speed WTSs at different stations in Turkey are also analysed and results are given.
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    A New Model for Wind Turbine Systems
    (TAYLOR & FRANCIS INC, 2009) Eminoglu, Ulas
    In this article, a new model for wind turbine systems with asynchronous generator is proposed. The model is developed by using the steady-state model of an induction machine. It is validated with an experimental setup composed by an induction generator coupled with an induction motor as a prime mover, and it is also tested on a simulation system. Results are also compared with the results of the other models reported in the literature for both systems. It is concluded that the developed model is comparable with the existing ones. The main advantage of the model is that it facilitates the computation of real and reactive power outputs for a specified mechanical power input and terminal voltages in a simple way such that it does not require computation of any system parameters (i.e., rotor slip and/or current), which causes computational complexity.
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    A Robust Static Voltage Stability Index for Distribution Networks
    (PRAISE WORTHY PRIZE SRL, 2010) Eminoglu, Ulas
    In this paper, a new static voltage stability index is proposed for identifying the line or its corresponding bus on the verge of voltage collapse of distribution networks'. The index is developed by using the distribution line receiving end bus voltage formulation, and its adequacy is evaluated on a modern distribution test system which has voltage controlled bus (PV-bus). From analyses, it is observed that the proposed stability index correctly predict the critical line and its corresponding bus as well, and can provide useful information for the most sensitive line at any operating point of distribution networks. On the other hand, most of the existing voltage stability indices do not correctly estimate the critical bus or its corresponding line for this particular distribution network In addition, the estimation about the most critical bus or line by using these stability indices for the any operation point of radial systems may cause utilities a wrong conclusion on the critical bus or its corresponding line because they would be inadequate for assessing the most sensitive bus or line in such distribution networks. Copyright (C) 2010 Praise Worthy Prize S.r.l. - All rights reserved.
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    A robust static voltage stability index for distribution networks
    (Praise Worthy Prize S.r.l, 2010) Eminoglu, Ulas
    In this paper, a new static voltage stability index is proposed for identifying the line or its corresponding bus on the verge of voltage collapse of distribution networks. The index is developed by using the distribution line receiving end bus voltage formulation, and its adequacy is evaluated on a modern distribution test system which has voltage controlled bus (PV-bus). From analyses, it is observed that the proposed stability index correctly predict the critical line and its corresponding bus as well, and can provide useful information for the most sensitive line at any operating point of distribution networks. On the other hand, most of the existing voltage stability indices do not correctly estimate the critical bus or its corresponding line for this particular distribution network. In addition, the estimation about the most critical bus or line by using these stability indices for the any operation point of radial systems may cause utilities a wrong conclusion on the critical bus or its corresponding line because they would be inadequate for assessing the most sensitive bus or line in such distribution networks. © 2010 Praise Worthy Prize S.r.l. - All rights reserved.
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    Computation of Stability Delay Margin of Time-Delayed Generator Excitation Control System with a Stabilizing Transformer
    (HINDAWI PUBLISHING CORPORATION, 2014) Ayasun, Saffet; Eminoglu, Ulas; Sonmez, Sahin
    This paper investigates the effect of time delays on the stability of a generator excitation control system compensated with a stabilizing transformer known as rate feedback stabilizer to damp out oscillations. The time delays are due to the use of measurement devices and communication links for data transfer. An analytical method is presented to compute the delay margin for stability. The delay margin is the maximum amount of time delay that the system can tolerate before it becomes unstable. First, without using any approximation, the transcendental characteristic equation is converted into a polynomial without the transcendentality such that its real roots coincide with the imaginary roots of the characteristic equation exactly. The resulting polynomial also enables us to easily determine the delay dependency of the system stability and the sensitivities of crossing roots with respect to the time delay. Then, an expression in terms of system parameters and imaginary root of the characteristic equation is derived for computing the delay margin. Theoretical delay margins are computed for a wide range of controller gains and their accuracy is verified by performing simulation studies. Results indicate that the addition of a stabilizing transformer to the excitation system increases the delay margin and improves the system damping significantly.
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    Incorporation of a New Wind Turbine Generating System Model into Distribution Systems Load Flow Analysis
    (WILEY-BLACKWELL, 2009) Eminoglu, Ulas; Dursun, Bahtiyar; Hocaoglu, M. Hakan
    This paper describes a new model for wind turbine generating systems (WTGSs) that is widely used as distributed generation sources. The model is developed by using the bi-quadratic equation, which is generally used for the calculation of the line voltages in distribution systems' load flow analysis, and facilitates computation of real and reactive power outputs of the WTGSs for a specified wind speed and terminal voltage. The developed model is validated with an experimental setup composed by an induction generator coupled with an induction motor as a prime mover. In addition to that measured values, are also compared with the calculated values, obtained by using the turbine models found in the literature. The incorporation of the developed model into some well-known distribution systems' load flow algorithms is detailed. The effect of WTGSs on the power losses, voltage profile of radial distribution systems are evaluated for the sample test systems. Additionally, the performance of the load flow algorithms with the new model are examined and found to be robust and reliable. Copyright (C) 2008 John Wiley & Sons, Ltd.
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    Modeling and application of wind turbine generating system (WTGS) to distribution systems
    (PERGAMON-ELSEVIER SCIENCE LTD, 2009) Eminoglu, Ulas
    This paper describes two new models for wind turbine generating systems (WTGSs), widely used as distributed generation sources in distribution systems. These models are developed by using the modifications of bi-quadratic equation which is generally used for the calculation of node voltages in distribution systems' load flow analysis. The developed models are validated with an experimental setup composed by an induction generator coupled with an induction motor as a prime mover, and with the calculated values obtained by using the other models reported in the literature. They are also incorporated into distribution systems' load flow analysis, and the results are compared with the results of their Simulink models. Simulink models are developed in Matlab using SimPowerSystems Blockset. (C) 2009 Elsevier Ltd. All rights reserved.
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    Modeling and Design Optimization of Variable-Speed Wind Turbine Systems
    (MDPI AG, 2014) Eminoglu, Ulas; Ayasun, Saffet
    As a result of the increase in energy demand and government subsidies, the usage of wind turbine system (WTS) has increased dramatically. Due to the higher energy production of a variable-speed WTS as compared to a fixed-speed WTS, the demand for this type of WTS has increased. In this study, a new method for the calculation of the power output of variable-speed WTSs is proposed. The proposed model is developed from the S-type curve used for population growth, and is only a function of the rated power and rated (nominal) wind speed. It has the advantage of enabling the user to calculate power output without using the rotor power coefficient. Additionally, by using the developed model, a mathematical method to calculate the value of rated wind speed in terms of turbine capacity factor and the scale parameter of the Weibull distribution for a given wind site is also proposed. Design optimization studies are performed by using the particle swarm optimization (PSO) and artificial bee colony (ABC) algorithms, which are applied into this type of problem for the first time. Different sites such as Northern and Mediterranean sites of Europe have been studied. Analyses for various parameters are also presented in order to evaluate the effect of rated wind speed on the design parameters and produced energy cost. Results show that proposed models are reliable and very useful for modeling and optimization of WTSs design by taking into account the wind potential of the region. Results also show that the PSO algorithm has better performance than the ABC algorithm for this type of problem.
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    Site-specific design optimization of horizontal-axis wind turbine systems using PSO algorithm
    (TUBITAK SCIENTIFIC & TECHNICAL RESEARCH COUNCIL TURKEY, 2016) Eminoglu, Ulas
    Due to the complexity of wind turbine systems (WTSs) containing multiple components, design parameters of a WTS must match each other in order to produce electrical energy at a lower cost and a higher efficiency. In this study, a framework for site-specific design optimization of a horizontal-axis WTS is proposed. It is based on cost reduction and the objective function is the produced energy cost. The cost of energy model proposed by the National Renewable Energy Laboratory is utilized. In order to compute turbine output power that results in annual energy production, a new approach is proposed to model the power coefficient of rotor for fixed-speed WTSs. Design optimizations are performed by using a particle swarm optimization algorithm, which appears to be efficient for this type of problem. WTSs in northern Europe and the Mediterranean were studied. Results show that optimized WTSs for these sites have high profitability in terms of cost and amount of energy when compared with reference WTSs installed in these sites. Parametric analyses are also undertaken in order to evaluate the effect of wind characteristics on the produced energy cost for both types of WTSs and the effects of rotor tip-speed ratio and turbine-rated power on the design parameters and produced energy cost for fixed-speed WTSs. It is concluded that rotor tip-speed ratio has strong effects on design wind speed for fixed-speed WTSs and on the cost of kWh.
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    Three-phase transformer and voltage regulator modelling for forward/backward sweep-based distribution system power flow algorithms
    (SAGE PUBLICATIONS LTD, 2009) Eminoglu, Ulas; Hocaoglu, M. Hakan
    This paper describes a new approach for modelling of a distribution transformer and automatic voltage regulator in forward/backward sweep-based algorithms for unbalanced radial distribution systems. For the transformer modelling a symmetrical components model is used and zero sequence voltage and current updating for the sweep-based methods are demonstrated. The validity and effectiveness of the proposed method is demonstrated in a simple two-bus system for grounded wye-delta and delta-grounded wye transformer connections. The automatic voltage regulators (AVRs) are included into the sweep-based methods and tested by using two distribution test systems. From the systems, all results are in agreement, the proposed model is valid and reliable, and the performance of the algorithms is less affected from the inclusion of regulator modelling.
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    Transmission line shunt and series compensation with voltage sensitive loads
    (MANCHESTER UNIV PRESS, 2009) Eminoglu, Ulas; Hocaoglu, M. Hakan; Yalcinoz, Tankut
    This paper presents an analysis of the effects of shunt and series line compensation levels on the transmission line voltage profile, transferred power and transmission losses for different static load models. For this purpose, a simple model is developed to calculate the series and/or shunt compensated transmission line load voltage. Consequently, different shunt and series compensation levels are used with several voltage sensitive load models for two different line models. It is observed that the compensation level is significantly affected by the voltage sensitivities of loads. Moreover, the voltage level of the transmission is an important issue for the selection of the shunt and series capacitor sizes when load voltage dependency is used.