Browsing by Author "Iskender, Ires"

Now showing 1 - 15 of 15

Citation - WoS: 2
Citation - Scopus: 4
A Novel Transformerless Single-Phase Three-Level Buck-Boost Inverter
(Ieee, 2023) Demirkutlu, Eyyup; Iskender, Ires; 133746
This paper proposes a novel transformerless, single-phase, three-level, buck-boost inverter. The proposed inverter can suppress the leakage current drawn from the input power source and provide a long-lasting solution for applications with a wide range and unregulated input voltage. Unlike similar topologies, in the proposed inverter there is no need to have a mid-point of DC sources or DC bus capacitors at the input side of the inverter. A single-phase, three-level, buck-boost inverter for realizing the power stage with 110-Vrms output AC voltage and a range of 100V-200V input DC voltage is investigated in this study. The proposed topology has been proven through theory, computer simulations, and experimental studies with SiC MOSFETs-based prototype of a 300-VA power supply. Theory, computer simulation, and experimental results are all correlated.
Citation - WoS: 0
Citation - Scopus: 1
Analysis of Lightning Impulse Effects on Three Winding Transformer Used in Solar System Based ANSYS Maxwell
(Ieee, 2022) Yukselen, Emir; İskender, İres; Iskender, Ires; 133746
Transformers are in more critical applications in the renewable energy world and having a transformer fail in such a cyclical power station can be disastrous. Over voltage or voltage strike is the most important phenomena for the transformers. Thus, the evaluating and estimating the effects and stresses of these sudden high voltages is important during the transformers life time operation and design stage. Accordingly in this paper the electromagnetic field analyses of the lightning impulse on Photovoltaic (PV) transformer are investigated using ANSYS Maxwell software. The 3D and 2D model simulation of the PV transformer is carried out to determine the electric field and voltage distribution on critical regions which can cause breakdown on insulation material and damage transformer windings and affects transformer working. Afterwards according to the simulation result, the subjected transformer was designed considering the relative critical regions and performs the full wave lightning impulse test in factory area to verify the dielectric strength of the transformer. This study provides better understanding of the lightning impulse voltage effects with localization of the critical regions on the PV transformer and helps to improve the withstand capability of the transformer against the lightning impulse voltages during the design and production stage.
Citation - WoS: 1
Citation - Scopus: 3
CASE 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) Yukselen, Emir; İskender, İres; Iskender, Ires; 133746
Transformers 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.
Citation - WoS: 6
Citation - Scopus: 7
Coreloss Estimation via Long Short-Term Memory Model (LSTM) of Dry-Type Transformer based on FEA
(Ieee, 2021) Kul, Seda; İskender, İres; Yildiz, Berat; Tamyurek, Bunyamin; Iskender, Ires; 133746
Accurate estimation of losses is very important in transformer designs for energy systems. Therefore, in this study, a long short-term memory model (LSTM) was performed to predict the core loss of three-phase dry-type transformers based on Finite Element Analysis (FEA) analysis. Since, in ordinary multilayer networks, learning problems occur when the gradient value gets too small during backpropagation. LSTM, on the other hand, can store information better thanks to its extra layers that communicate. Thus, the learning process takes place more efficiently. The analysis and estimation processes were performed using a primary number of turns, excitation voltage, and three different cross-section area parameters. 486 data randomly selected from 506 data obtained by ANSYS/MAXWELL in the training of the LSTM model were used. The remaining 20 data were used in the testing process to measure system performance. The error obtained by the validation test is 0.15. It is very close to the simulated value, thus LSTM can be used as a reliable estimation method during the design stage.
Citation - WoS: 0
Citation - Scopus: 0
Design of a Novel Converter Between Li-Ion Battery and Supercapacitor to Feed Synthetic Aperture Radar Loads for Satellite Applications
(int Journal Renewable Energy Research, 2020) Tulay, Gencer; İskender, İres; Iskender, Ires; 133746
For satellite applications the active duty life of a satellite depends mainly on the battery lifespan. The charging or discharging current has an important role in useful life of batteries. For this purpose, the converters used in power supplies including batteries should be accurately designed such that the large current of batteries can be prevented. The power converter proposed in this paper is used to transfer energy from battery to supercapacitor when SAR (Synthetic Aperture Radar) load is active. Accordingly, the lifespan of battery and hence the lifespan of satellite will be extended. Parallel to preventing the large discharging current of batteries the proposed converter has another important property such that it is able to vary the input voltage without having any stability problems. The operating performance of the converter that is composed of Weinberg and Buck converters is analyzed using PSpice software and the results of simulations are verified through experiments. The results show that how well the converter operates satisfying the conditions required for satellite applications.
Citation - WoS: 1
Citation - Scopus: 1
Design Studies of VSC HVDC Converter According to AC Voltage Tests
(Mdpi, 2022) Haliloglu, Ali Burhan; İskender, İres; Iskender, Ires; 133746
Since high-voltage direct current (HVDC) systems are very expensive and operationally critical, these systems must be tested before they are put into service. Insulation and performance tests are the two main subjects of these tests. AC voltage tests, as part of the insulation tests, should be performed after system installation is complete and before commissioning. However, in this study, the objective was to perform these tests during the prototype phase of VSC HVDC. Unlike other studies, this study attempted to use COMSOL Multiphysics to determine in advance the problems that may occur in the real system. In this regard, the busbars connecting the submodules of the VSC HVDC system were first modeled in 3D, and the tests to be performed were simulated using COMSOL Multiphysics software. During the simulation, the finite element method (FEM) was used to identify critical points that could cause partial discharge. To validate the simulation results, partial discharge tests on a real system were conducted, and the design changes made in response to each test result were explained. After the improvement actions, the targeted partial discharge values were achieved.
Citation - WoS: 0
Citation - Scopus: 4
FEA Simulation of the Electromagnetic Effects on the Flux Distribution of the Joints in the Transformer Core Structure
(Ieee, 2018) Kul, Seda; İskender, İres; Iskender, Ires; Balci, Selami; 133746
In the manufacturing of the transformer the occurrence of air gaps at the joints of the legs and yokes of the core lamination stacking of the transformers is inevitable. The air-gap in the core joints affects the magnetic flux density and the magnetic flux distribution in the core. The location, shape, length and number of air-gaps all are different from each other. The increase in air-gap of transformer core will increase the reluctance of the core causing a reduction in the total magnetic flux value. The effects of the air-gap in joints cannot be exactly analyzed mathematically. However, the electromagnetic modeling using the finite element method provides facility to simulate and analyze such a problem. In this study, the effects of air-gaps with different shapes and length in the transformer legs on the stray magnetic are compared with using Finite Element Analysis (FEA) software.
Citation - WoS: 1
Citation - Scopus: 3
FEM-based optimal design and testing of synchronous magnetic coupling for aerospace Starter/Generator applications
(Elsevier - Division Reed Elsevier india Pvt Ltd, 2023) Arslan, Sami; İskender, İres; Iskender, Ires; Navruz, Tugba Selcen; 133746
Improvements in high energy density rare-earth permanent magnets make it innovative to develop magnetic couplings for Starter/Generator applications in the light of more electric aircraft to ensure magnetically insulated contactless power transmission between decoupled shafts for safe operation. Although there are essential studies on magnetic couplings in the literature, especially those for aerospace Starter/Generator structures are rarely encountered. However, methodologies considering system constraints and examining design parameters of couplings are in demand. In response to such a need, this paper proposes the novel design of highly reliable synchronous radial magnetic couplings with torque requirements of 6 and 12 N.m to isolate Starter/Generator and piston engine shafts in model aircraft. The preliminary volume is obtained analytically. Simulations are executed by optimetric approaches in Ansys Maxwell 2D. Optimisation techniques are compared in Maxwell 3D to get the final shape. The retaining sleeve of 0.5 mm is suggested. Loss of synchronisation in the event of the piston shaft failure or exceeding the maximum torque of the coupling is also examined. The torque fluctuation at load changes is 0.1%. Performance tests are conducted on the direct dynamic test bench. Absolute error margin is 37% for the Virtual Work method, 13% for 2D FEM and 6% for 3D FEM. The coupling efficiency is 93.8% at the maximum operating speed and the critical angle, and 96.9% at the minimum torque angle and the minimum operating speed.(c) 2023 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Citation - WoS: 1
Citation - Scopus: 1
Finite Element Method-Based Optimisation of Magnetic Coupler Design for Safe Operation of Hybrid UAVs
(Mdpi, 2023) Arslan, Sami; İskender, İres; Iskender, Ires; Navruz, Tugba Selcen; 133746
The integration of compact concepts and advances in permanent-magnet technology improve the safety, usability, endurance, and simplicity of unmanned aerial vehicles (UAVs) while also providing long-term operation without maintenance and larger air gap use. These developments have revealed the demand for the use of magnetic couplers to magnetically isolate aircraft engines and starter-generator shafts, allowing contactless torque transmission. This paper explores the design aspects of an active cylindrical-type magnetic coupler based on finite element analyses to achieve an optimum model for hybrid UAVs using a piston engine. The novel model is parameterised in Ansys Maxwell for optimetric solutions, including magnetostatics and transients. The criteria of material selection, coupler types, and topologies are discussed. The Torque-Speed bench is set up for dynamic and static tests. The highest torque density is obtained in the 10-pole configuration with an embrace of 0.98. In addition, the loss of synchronisation caused by the piston engine shaft locking and misalignment in the case of bearing problems is also examined. The magnetic coupler efficiency is above 94% at the maximum speed. The error margin of the numerical simulations is 8% for the Maxwell 2D and 4.5% for 3D. Correction coefficients of 1.2 for the Maxwell 2D and 1.1 for 3D are proposed.
Citation - WoS: 3
Citation - Scopus: 5
Grid Connected Three-Phase Boost-Inverter for Solar PV Systems
(int Journal Renewable Energy Research, 2021) Demirkutlu, Eyyup; İskender, İres; Iskender, Ires; 133746
This paper presents a transformerless grid-connected three-phase boost-type inverter derived from the Swiss Rectifier (SR) and can be used in solar systems. The proposed boost-inverter retains the great advantages of the Swiss rectifier. Since the number of switches that are instantly switched with high frequency is only two, the switching losses are very low, therefore the proposed boost-inverter is very advantageous in terms of efficiency. Without having large transformer and electrolytic bus capacitors, the boost-inverter has an advantage in terms of size and weight. The switching states of the topology are given in detail. The operation principle of the boost-inverter is described with the help of equivalent circuits. A cascaded control method including current and voltage loops is designed. Simulation results are presented to validate the operation of the boost-inverter and show quality performance of the designed control approach.
Citation - WoS: 0
Citation - Scopus: 0
Non-Linear Eddy Current Loss and Thermal Analysis on Transformer Cover
(Gazi Univ, 2019) Zahedi, Mohammad Zia; İskender, İres; Iskender, Ires; 133746
High current conductors of transformers cause to produce losses and thermal problems in their tank cover. Finite Difference (FD) Method (FDM) magnetic analysis is used to find out an exact estimation of the magnetic field and the losses near the bushings in the transient solution, considering the non-linear magnetic permeability of the cover plate, because FDM is more flexible to deal with the nonlinear constitutive law and easy-to-be implemented especially in the case of simple geometry. Finite Element Method (FEM) thermal analysis is used to determine the plate temperature based on magnetic FD analysis, taking account non-linear heat flux boundary condition. A calibration procedure is used between the analyses to ensure the precision of assumptions. The reliability of the technique, confirmed by experimental and FEM results.
Citation - WoS: 9
Citation - Scopus: 12
Power Electronic Converters in DC Microgrid
(Springer international Publishing Ag, 2020) Iskender, Ires; İskender, İres; Genc, Naci; 133746
There are not many sustainable sources of energy other than renewable energy sources (RES), which are called solar, wind, water and various forms of biomass. Themost effectiveway to increase the use of renewable energy sources is to make use of renewable energy systems in villages, townships or small island-shaped districts where there are significant amounts of energy consumers. For this reason, the microgrid (MG) idea of small power system which is controllable, autonomous and balanced has been developed. Microgrids (MGs) playing a role of carrier for distributed generation resources (DGR), includes different distributed generation (DG) units, storage devices, energy converters, protection devices and load control devices. A MG generally includes renewable small power sources consisting of interconnected distributed energy sources with capacity of providing sufficient and sustained energy for a significant portion of the load. Different architecture types of MGs are presented in the literature. In recent years, the use of MGs being able to operate in two different modes depending on the island and grid-connected, has been expanded for DGR integration. Direct current (DC) microgrid has become an important subject of study in recent years as they have a more reliable and lower losses. A DC MG task distributes the DC power required by loads on a campus. Power generation in DC MG systems can be AC or DC; however, in most cases AC power supplies is converted to DC for distribution. The major advantage of DC microgridswhen compared toACsystems is its property of unidirectional power flow. This allows power control to be easily controlled by the power flow direction. In DC MG, the loads must be controllable to keep all loads at the DC range of the voltage in the default range and to regulate the voltage regulation. Besides voltage level and voltage regulation, the voltage ripple ratio should be kept as low as possible in DC microgrids. Therefore, power electronic converters are themost important part of the DC MG systems. There are although many studies published on MGs that control strategy and power electronic circuits make their important portions. It is obvious that the development of power electronic circuits and control methods has further enhanced the applicability of microgrids. In this study, the types, circuit structures and functions of power electronic converters used in DC microgrid are discussed. Power electronics converters used in DC MGs are grouped and evaluated according to their targets. These power electronic converters have been detailed in terms of AC-DC rectifiers, inverters (for AC loads) and DC-DC converter circuit types. The simulation results of some topologies have been evaluated.
Citation - WoS: 0
Citation - Scopus: 1
Surge Arrester Allocation for Lightning Protection of Vsc Based Hvdc Prototype
(Elsevier - Division Reed Elsevier india Pvt Ltd, 2023) Haliloglu, Ali Burhan; Iskender, Ires
High-voltage direct current (HVDC) systems, based on voltage source converters (VSC), enable asynchronous interconnection of grids with different frequencies and contribute to grid stability by controlling power quickly and precisely. Effective protection of these expensive systems, which must be in continuous operation, increases their lifetime. An overvoltage protection study is needed to ensure the proper protection of HVDC systems that contain multiple devices with varying insulation levels. In this study, lightning protection studies on a prototype VSC-based HVDC (VSC-HVDC) system are explained. In line with this, lightning impulses were modeled and applied to various points in the PSCAD model of the prototype VSC-HVDC, and the response of the system combined with the protection equipment was examined. All stages of protective equipment selection were explained step by step. The suitability of the selected protective equipment was verified based on the simulation results. After running dozens of scenarios, the protection coordination was optimized, and the critical points were determined instead of installing surge arresters at each connection point. In this way, a significant cost benefit was obtained for the investment in protective equipment. Finally, the results of the lightning impulse tests performed to verify the insulation of the VSC-HVDC prototype are reported.
Citation - WoS: 2
Citation - Scopus: 4
Transformerless Single-Phase Buck-Boost Inverter Decoupled From the Midpoint of the Input Dc Capacitors
(Ieee-inst Electrical Electronics Engineers inc, 2024) Demirkutlu, Eyyup; Iskender, Ires
A transformerless, single-phase, buck-boost inverter is proposed in this study. Unlike similar topologies, the proposed inverter does not need to have a mid-point of dc sources or dc-bus capacitors at the input side of the inverter. The proposed inverter can suppress the leakage current drawn from the input power source and provide a long-lasting solution for applications with a wide input voltage range and/or unregulated input voltage. This article presents the controller and modulation design details, and a comparative evaluation conducted for the proposed inverter. A single-phase, buck-boost inverter for realizing the power stage with 110 V-rms output ac voltage and a range of 100-200 V input dc voltage is investigated in this study. The proposed inverter has been proven through theory, computer simulations, and experimental studies with SiC MOSFETS-based prototype of a 300 VA power supply. Theory, computer simulation, and experimental results are all correlated.
Citation - WoS: 0
Citation - Scopus: 1
Unbalanced Operation in Transformers Used in PV Plants
(int Journal Renewable Energy Research, 2022) Yukselen, Emir; Iskender, Ires; 133746
energy has become the most preferred energy sources today due to its environmental and economic advantages. One of the renewable energies is solar energy, in which Photovoltaic (PV) cells are used to convert solar energy into electrical energy. In this respect, Solar Power Plant (SPP) is one of the popular renewable energy sources and the integration of such power sources into electricity grids has been increasing in recent years. Transformers are one of the largest capital investments in solar power generation and the way they work is different from transformers used in a substation. Therefore, failure of transformers has significant economic effects on electrical networks. The PV type transformer is powered by the inverter and needs to be customized to work with every system. Consequently, the safe operation and reliability of this type of transformer is critical to the sustainability of the electrical grid. Consequently, identifying the probability of failure as a preventative action for grid protection is critical and should be addressed to improve electrical system reliability. The main purpose of this study is to analyze the effects of the unbalanced operation of the inverter on the performance of the special type transformer used in the PV plant and to show how the inverter operation can affect the operation of the transformer.