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grid-connected-photovoltaic-system
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Comparison of common-mode voltage in three-phase quasi-Z-source inverters using different shoot-through implementation methods
, Article Proceedings - 2018 IEEE 12th International Conference on Compatibility, Power Electronics and Power Engineering, CPE-POWERENG 2018 ; 4 June , 2018 , Pages 1-6 ; 9781538625088 (ISBN) ; Zolghadri, M. R ; Yaghoubi, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
In Z-source family inverters, shoot-through (ST) states are applied as a part of passive state in each switching cycle. The distribution of ST intervals along a switching period affects the system parameters as total harmonic distortion (THD), switching loss and common-mode voltage (CMV). In this paper, ST methods in a three-phase quasi-Z-source inverter (q-ZSI) are compared due to the CMV level. High-frequency harmonics of CMV cause leakage current flow in a transformerless grid-connected photovoltaic (PV) system. Through the comparison of the ST methods, the method with minimum CMV is identified. The experimental results are Prasented for a low voltage q-ZSI prototype. © 2018 IEEE
Design and Implementation of a Modular 3-Ph Grid Connected Solar Inverter
, M.Sc. Thesis Sharif University of Technology ; Zolghadri, Mohammad Reza (Supervisor) ; Attarodi, Mojtaba (Co-Supervisor)
Abstract
Recently a new topology, namely “common ground inverter” is introduced which since it enjoys a direct connection between AC neutral and DC ground, essentially solves the problem of leakage current in grid connected applications. Moreover, a reduced implementation price and a simple control scheme is associated with this system. The Aforementioned features have absorbed a lot of attention for further research regarding this topology. In this research one of the three introduced topologies is considered in details and its function in supplying local loads and Grid is put to the test. Moreover, important efforts have been taken to improve the properties of the inverter in terms of efficiency,...
Performance Improvement of Grid-connected Quasi-Z-Source Photovoltaic Inverter to Reduce Leakage Currents
, Ph.D. Dissertation Sharif University of Technology ; Zolghadri, Mohammad Reza (Supervisor)
Abstract
A quasi-Z-source inverter is a beneficial structure in photovoltaic applications. In a transformerless grid-connected inverter system, the common-mode voltage fluctuations cause the leakage current flow through the ground. The low-frequency harmonics of the common-mode voltage results in the malfunction of the residual current device. On the other hand, the high-frequency harmonics of the common-mode voltage cause EMI problems, additional loss and disturbance in the output currents. In this thesis, some methods are presented to reduce the leakage current in a three-phase quasi-Z-source inverter. First, different shoot-through implementation methods are investigated. By modifying the number...
Prevention of distribution network overvoltage by adaptive droop-based active and reactive power control of PV systems
, Article Electric Power Systems Research ; Volume 133 , 2016 , Pages 313-327 ; 03787796 (ISSN) ; Parniani, M ; Sharif University of Technology
Elsevier Ltd
Abstract
Proliferation of grid-connected photovoltaic systems (PVSs) causes technical problems due to their variable and non-dispatchable generated power. High penetration of PVS in distribution networks can result in overvoltage in some operating conditions. Although this situation occurs rarely, it limits the installed capacity of PVS. In this paper, adaptive droop-based control algorithms are presented to regulate active and reactive power of PVS, with the objectives of loss minimization and increasing the PVS capacity installation without unallowable overvoltage. Operating voltage range of the PVS is divided into several intervals, and a specific control algorithm is presented for each of them....
Three-phase quasi-Z-source inverter with constant common-mode voltage for photovoltaic application
, Article IEEE Transactions on Industrial Electronics ; 2017 ; 02780046 (ISSN) ; Zolghadri, M. R ; Sharif University of Technology
Abstract
In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through (SH) states in a quasi-Z-source inverter (q-ZSI), increase the amplitude of high order harmonics of CMV. In this paper, by using the modulation technique based on odd PWM (OPWM) and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. IEEE
A novel modulation method for reducing common mode voltage in three-phase inverters
, Article Conference Proceedings - 2017 17th IEEE International Conference on Environment and Electrical Engineering and 2017 1st IEEE Industrial and Commercial Power Systems Europe, EEEIC / I and CPS Europe 2017, 6 June 2017 through 9 June 2017 ; 2017 ; 9781538639160 (ISBN) ; Zolghadri, M. R ; Yaghoubi, M ; Sharif University of Technology
Abstract
Leakage current is originated from common-mode voltage (CMV) time variations in a grid-connected photovoltaic (PV) system and results in several deficiencies. In this paper, a new method is proposed for CMV reduction in a three-phase voltage source inverter (VSI) system. The proposed method is based on space vector modulation and it utilizes only odd and zero vectors. By using the proposed method, the number of fluctuations of the CMV waveform per switching cycle is reduced; therefore, the amount of high-frequency harmonics of CMV is decreased. In addition, because of applying both active and zero vectors by the proposed method, the total harmonic distortion becomes less than most of other...
A modulation method for leakage current reduction in a three-phase grid-tie quasi-Z-source inverter
, Article IEEE Transactions on Power Electronics ; 2018 ; 08858993 (ISSN) ; Yaghoubi, M ; Zolghadri, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
The leakage current originated from the fluctuations of the common-mode voltage (CMV) is an issue in a transformerless grid-connected photovoltaic (PV) system. In this paper, a modified space vector modulation based on the Fourier transform analysis is proposed to reduce the leakage current in a three-phase quasi-Z-source inverter (qZSI). The CMV harmonic content in a qZSI contains low and high-frequency harmonics which cause safety and EMI problems respectively. By implementing the proposed modulation in a three-phase qZSI, the low-frequency harmonics of the CMV are mainly reduced. The distribution of the high-frequency harmonics is also modified in a way they can be simply filtered....
Three-Phase quasi-Z-source inverter with constant common-mode voltage for photovoltaic application
, Article IEEE Transactions on Industrial Electronics ; Volume 65, Issue 6 , 2018 , Pages 4790-4798 ; 02780046 (ISSN) ; Zolghadri, M. R ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through states in a quasi-Z-source inverter (q-ZSI) increase the amplitude of high-order harmonics of CMV. In this paper, by using the modulation technique based on odd pulse width modulation and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. ©...
A modulation method for leakage current reduction in a three-phase grid-tie quasi-z-source inverter
, Article IEEE Transactions on Power Electronics ; Volume 34, Issue 6 , 2019 , Pages 5439-5450 ; 08858993 (ISSN) ; Yaghoubi, M ; Zolghadri, M. R ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
The leakage current originated from the fluctuations of the common-mode voltage (CMV) is an issue in a transformerless grid-connected photovoltaic system. In this paper, a modified space vector modulation based on the Fourier transform analysis is proposed to reduce the leakage current in a three-phase quasi-Z-source inverter (qZSI). The CMV harmonic content in a qZSI contains low-and high-frequency harmonics that cause safety and electromagnetic interference problems, respectively. By implementing the proposed modulation in a three-phase qZSI, the low-frequency harmonics of the CMV are mainly reduced. The distribution of the high-frequency harmonics is also modified in a way they can be...
Harmonic analysis of common-mode voltage in quasi-z-source inverters
, Article 2019 IEEE International Conference on Industrial Technology, ICIT 2019, 13 February 2019 through 15 February 2019 ; Volume 2019-February , 2019 , Pages 1778-1783 ; 9781538663769 (ISBN) ; Yaghoubi, M ; Davoodi, A ; Ouni, S ; Zolghadri, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
In a transformerless grid-connected photovoltaic system, many issues arise from the leakage current flow into the ground, as EMI problems. The leakage current is originated from the common-mode voltage fluctuations. In this paper, the common-mode voltage harmonics in a three-phase quasi-Z-source inverter are analyzed using Fourier transform and a closed-loop formulation is presented for the harmonics value. The shoot-through mode in a quasi-Z-source inverter causes extra fluctuations in the common-mode voltage comparing to a classic inverter. The proposed harmonic analysis method provides a systematic way to figure out how shoot-through mode and also other parameters affect the common-mode...
Stability and performance analysis of a single-stage grid-connected photovoltaic system using describing function theory
, Article International Transactions on Electrical Energy Systems ; Volume 26, Issue 9 , 2016 , Pages 1898-1916 ; 20507038 (ISSN) ; Mokhtari, H ; Karimi, S ; Azizian, M. R ; Sharif University of Technology
John Wiley and Sons Ltd
Abstract
Challenging problems in the design and analysis of photovoltaic (PV) systems stem from the nonlinear current–voltage (I–V) characteristics of solar cells. This paper presents an analytical analysis based on a describing function method to investigate the transient and steady-state characteristics of a three-phase single-stage grid-connected PV system. In this study, the nonlinear I–V characteristic of the PV array is linearized around the operating point. The nonlinear dynamic of the maximum power point tracking controller is divided into two parts of continuous and discrete. For the continuous part, the common small-signal linearization is applied, while for the discontinuous part, a...