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Design and Implementation of Transformerless Grid Connected PV Inverter with Mitigating Leakage Currents
, M.Sc. Thesis Sharif University of Technology ; Zolghadri, Mohammad Reza (Supervisor)
Abstract
In recent years Photovoltaic Panels (PV) are very wide spread. Due to AC working mode of many consumers produce DC voltage of PV must be converted to AC voltage by inverters. Nowdays one of the most popular inverter topologies are grid connected transformerless inverters. The main task of transformer is galvanic isolation of PV from grid. These transformers are commonly work with grid frequency i.e 50 Hz, and consequently are bulky, heavy and expensive. Transformer elimination results in common mode leakage current from parasitic capacitors of PV cells and its grounded frame to the grid ground, that will cause in EMI and malfunction of earth fault relays.
In this thesis the factors of...
In this thesis the factors of...
A simplified implementation of NLSPWM control strategy for SqZS inverter via model-driven processor programming method
, Article International Journal of Circuit Theory and Applications ; Volume 50, Issue 8 , 2022 , Pages 2687-2708 ; 00989886 (ISSN) ; Haghjoo, F ; Javadi, H ; Zolghadri, M. R ; Sharif University of Technology
John Wiley and Sons Ltd
2022
Abstract
The transformerless single-phase semi-quasi-Z-source inverter (SqZSI) has a nonlinear gain curve and requires nonlinear sinusoidal pulse width modulation (NLSPWM) to achieve sinusoidal voltage at the output AC terminal. Although the SqZSI provides some advantages, for example, leakage current elimination, doubly grounded, low volume, and low cost, it needs nonlinear modulation control. The NLSPWM is relatively complex among single-phase modulation methods and it is considered a disadvantage for this topology, so this paper presents a model-driven processor programming method that facilitates the implementation of NLSPWM. The developed programming method utilizes a Blockset environment in...
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...
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...