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  1. Ana Sayfa
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Yazar "Uçar, Mehmet" seçeneğine göre listele

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    3-Phase 4-leg unified series-parallel active filter system with ultracapacitor energy storage for unbalanced voltage sag mitigation
    (Elsevier Sci Ltd, 2013) Uçar, Mehmet; Özdemir, Şule
    This paper presents the analysis and design of a 3-phase 4-leg (3P4L) unified series-parallel active filter (USPAF) with ultracapacitor energy storage (UCES) for improving the power quality in three-phase four-wire (3P4W) distribution system. The series and parallel active filter (AF) of 3P4L USPAF system are realized by four-leg voltage source inverters (VSIs) to a common dc-link capacitor. Due to its high power density, the UCES is well-suited to supply high power for short period of time. The objective of this paper is to enhance the unbalanced voltage sag mitigating capability of the 3P4L USPAF system by adding UCES, directly connected in the dc-link. This is achieved by injecting energy from the UCES to maintain the dc-link voltage constant. Thus, the proposed system is capable of mitigating unbalanced voltage sag with zero-sequence component in the source voltage and compensating harmonic, reactive power and unbalanced current of the load in 3P4W distribution systems. The proposed scheme is validated by an experimental prototype with a 1.93 F UCES bank and using dSPACE DS1103 real-time control platform in the laboratory. The experimental results show that the combined system offer improved performance to maintain the load voltage constant at its rated value during unbalanced voltage sag in the supply voltage. (C) 2013 Elsevier Ltd. All rights reserved.
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    Analysis and design of grid-connected 3-phase 3-level AT-NPC inverter for low-voltage applications
    (Tubitak Scientific & Technical Research Council Turkey, 2017) Avcı, Emre; Uçar, Mehmet
    The 3-level T-type neutral point clamped (T-NPC) inverter has become the most popular multilevel inverter used in low-voltage applications. However, the realization of a bidirectional switch located at the midpoint leg of the T-NPC inverter is achieved using two insulated gate bipolar transistors (IGBTs) with two antiparallel diodes. Power dissipation in these switches is high since there are two semiconductors (an IGBT and a diode) in the current path at the midpoint leg. Switch losses can be reduced and thus the highest conversion efficiency can be achieved if the bidirectional switches in the T-NPC inverter are replaced by highly efficient reverse-blocking IGBTs (RB-IGBTs). The objective of this paper is to assess the performance of a 3-phase 3-level grid-connected advanced T-NPC (AT-NPC) inverter with RBIGBT for low-voltage applications. This paper describes the operating principle of the grid-connected AT-NPC inverter, analyzes the power losses, and discusses the control strategy. A 1.7-kW laboratory prototype is designed and built to verify the feasibility and the effectiveness of the proposed 3-phase 3-level grid-connected AT-NPC inverter. Real-time control of the inverter is experimentally achieved using a dSPACE DS1103 controller. The experimental results show that the efficiency of the proposed grid-connected inverter is about 96.3%.
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    Design and operation of a multifunction photovoltaic power system with shunt active filtering using a single-stage three-phase multilevel inverter
    (Tubitak Scientific & Technical Research Council Turkey, 2017) Sezen, Serkan; Aktaş, Ahmet; Uçar, Mehmet; Özdemir, Engin
    In this paper, the control of a multifunction grid-connected photovoltaic (PV) system with a three-phase three level (3L) neutral point clamped (NPC) inverter is proposed, which can perform shunt active filtering. Normally, the shunt active filtering is achieved by detecting the harmonic and reactive currents of the nonlinear load and then injecting the compensating current into the grid. Therefore, the proposed system can inject PV power to a grid with power factor correction and current harmonic filtering features simultaneously. In addition, a single-stage compact and efficient transformerless power conversion topology is used in this paper for the grid-connected solar PV system with maximum power point tracking capability. In order to control the multilevel inverter-based combined system, a synchronous reference frame control technique and hysteresis current control pulse width modulation method have been applied. The system configuration and control strategy are verified and validated by simulations based on MATLAB/Simulink and implemented in real-time using the dSPACE DS1103 controller board. The simulation with experimental results indicates that the injected currents are sinusoidal and current total harmonic distortion is about 3.9%, lower than the IEEE 519 harmonic limit.
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    Design and operation of a multifunction photovoltaic power system with shunt active ltering using a single-stage three-phase multilevel inverter
    (2017) Sezen, Serkan; Aktaş, Ahmet; Uçar, Mehmet; Özdemir, Engin
    In this paper, the control of a multifunction grid-connected photovoltaic (PV) system with a three-phase three- level (3L) neutral point clamped (NPC) inverter is proposed, which can perform shunt active ltering. Normally, the shunt active ltering is achieved by detecting the harmonic and reactive currents of the nonlinear load and then injecting the compensating current into the grid. Therefore, the proposed system can inject PV power to a grid with power factor correction and current harmonic ltering features simultaneously. In addition, a single-stage compact and efficient transformerless power conversion topology is used in this paper for the grid-connected solar PV system with maximum power point tracking capability. In order to control the multilevel inverter-based combined system, a synchronous reference frame control technique and hysteresis current control pulse width modulation method have been applied. The system con guration and control strategy are veri ed and validated by simulations based on MATLAB/Simulink and implemented in real-time using the dSPACE DS1103 controller board. The simulation with experimental results indicates that the injected currents are sinusoidal and current total harmonic distortion is about 3.9%, lower than the IEEE 519 harmonic limit.
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    Dual-Mode Operation of 3-Level 4-Leg AT-NPC Inverter for Microgrids
    (Institute of Electrical and Electronics Engineers Inc., 2019) Avcı, Emre; Uçar, Mehmet
    This study presents dual-mode operation and seamless transfer of 3-level 4-leg Advanced T-type Neutral Point Clamped (AT-NPC) inverter for low voltage microgrids. The proposed control technique is designed with Proportional Resonant (PR) based current controlled in grid-connected operation and with Proportional Multi Resonant (PMR) based voltage controlled in islanded operation. In order to ensure smooth transition between these operating modes, combined seamless transfer method is proposed. The proposed 3-phase 4-leg inverter system can supply both 1-phase and unbalanced 3-phase load groups in islanded mode. A laboratory prototype is installed for the experimental testing of the 3-phase 4-leg AT-NPC 3-level inverter system. The proposed system is simulated via PSIM software and the model-based embedded codes are generated with PSIM/SimCoder software. Real-time control algorithm of the inverter system is carried out with TMS320F28335 digital signal controller board. Finally, the operation performance of the inverter system is investigated both in the islanded/grid-connected mode and the seamless transfer process between these two operating modes. © 2019 IEEE.
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    MODÜLER ÇOK SEVİYELİ DÖNÜŞTÜRÜCÜLERİN İNCELENMESİ
    (Düzce Üniversitesi, 2016) Dündar, Ayhan; Uçar, Mehmet
    Modüler Çok Seviyeli Dönüştürücüler (MÇSD), farklı gerilim ve güç seviyesi gerektiren uygulamalar için modüler tasarımı ve kolay adaptasyonu ile son yıllarda endüstride oldukça ilgi çekmektedir. Bu çalışmada, MÇSD yapıları, alt modüllerin çalışma prensipleri ve anahtarlama işaretlerini üretmek için kullanılan çok taşıyıcılı darbe genişlik modülasyonu (PWM) yöntemleri incelenmiştir. Ayrıca üç fazlı beş seviyeli MÇSD denetimine ilişkin sonuçları değerlendirmek için MATLAB/Simulink benzetim sonuçları sunulmuştur
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    Operation and performance of grid-connected solar photovoltaic power system in Kocaeli university
    (Natl Inst Optoelectronics, 2013) Aktaş, Ahmet; Özdemir, Engin; Karakaya, Abdulhakim; Uçar, Mehmet
    In this study, operation and performance of grid-connected solar photovoltaic (PV) power system installed in Kocaeli University are presented. The grid-connected PV power system consists of 720 Wp thin-film PV panels, a 1 kW grid-connected inverter and a WebBox for internet connection. The PV system has been installed first 360 Wp in March 2010 and upgraded for 720 Wp in August 2011. Each has a power of 60 Wp Kaneka thin-film solar panels are installed in the PV system. The SMA Sunny Boy single-phase 1 kW grid-connected inverter is connected to perform the conversion of the direct current generated by the PV panels into mains standard alternating current. The power, voltage and current harmonic values at grid side of the inverter have been measured using Fluke 434 power quality analyzer. After March 2012, the PV system has Internet connection via SMA Sunny WebBox. The produced PV electric energy amount can be monitored in our department website (http://enerji.kocaeli.edu.tr) in hourly, daily and monthly basis.
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    SRF Based Output Voltage Control of 3-Level 3-Phase 4-Leg AT-NPC Inverter
    (Gazi Univ, 2018) Avcı, Emre; Uçar, Mehmet
    This paper proposes a synchronous reference frame (SRF) based high performance output voltage controller for the 3-level 3-phase 4-leg (3P4L) advanced T-type neutral point clamped (AT-NPC) inverter operated in stand-alone mode. 3-phase inverters for standalone operation are required to provide 3-phase balanced nominal voltage under different load types such as unbalanced linear and non-linear loads. 3P4L inverters working with these types of load allow controlling zero sequence voltage by additional fourth leg. The main contribution of this work is the control of the 3-level 3P4L AT-NPC inverter with an LC-type filter modeled based on the output voltage and capacitor current feedback in the synchronous coordinate system. According to obtained capacitor current decoupled model, double loop PI controller is adopted to control the output voltage of the inverter. An inner capacitor current feedback loop is employed to provide fast dynamic response and active damping of the capacitor current. Finally, transient and steady state operation performance of the controller have been tested with PSIM simulation studies considering different load types. Simulation results validate that the proposed SRF based double loop PI controller ensure high dynamic response and high quality output voltage with less than 3% total harmonic distortion (THD) value for the 3-level 3P4L AT-NPC inverter.
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    A Three-Phase Three-Level NPC Inverter Based Grid-Connected Photovoltaic System With Active Power Filtering
    (Ieee, 2014) Sezen, Serkan; Aktaş, Ahmet; Uçar, Mehmet; Özdemir, Engin
    This paper presents a three-phase three-level neutral point clamped (NPC) inverter based single-stage grid-connected photovoltaic (PV) system with shunt active power filter (APF) functionality. The proposed system can perform both the maximum real power injection with the perturb and observe (P&O) maximum power point tracking (MPPT) algorithm from the PV panels into the grid and active power filtering to compensate the load current harmonics. Thus, the PV system operates more efficiently compared to the conventional PV systems and can be useful for power system applications. Control of the proposed system is based on synchronous reference frame control algorithm and hysteresis band current control technique. The effectiveness of the proposed system is demonstrated with Matlab/Simulink simulations and validated through dSPACE DS1103 real-time control platform based laboratory experimental results.

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