Suppression Strategy Of Leakage Current And DC Injection For Non-isolated Photovoltaic Grid

Photovoltaic power generation system is one of the main measures to solve the problem of energy crisis and environmental pollution. Early photovoltaic power generation system is usually connected to the power frequency isolation transformer, however, due to its large volume, high cost and low efficiency,is gradually replaced by a non isolated photovoltaic grid connected inverter.Although the transformerless photovoltaic inverter has many advantages, it also brings new challenges, the leakage current and DC injection problem is the main issue to hinder the development of transformerless photovoltaic inverter,IEEE Std.929-2000 require that DC injection must be less than 0.5% of the rated current, the German VDE-0126-1-1 standard require that inverter leakage current is greater than 300 mA photovoltaic power generation system, need within 0.3s from the grid splitting. In order to solve the key technical problems,based on the single-phase photovoltaic grid connected inverter as the research object, and mainly studies on the mechanism and suppression strategy of leakage current and DC injection.Firstly, the mechanism of the leakage current of the single-phase photovoltaic grid connected inverter is researched in the paper, the topological structure of single-phase grid connected inverter is given to inhibit the leakage current, and its working principle and switching state are analyzed in detail. The simulation model was established by using the simulation software, and single-phase H bridge converter and high efficiency H6 topology is studied through simulation, and the feasibility is verified.Secondly, this paper researchs the cause and harm of DC injection,establishes mathematical model of single phase grid connected inverter;analysis' s several important factors that cause the DC component of the output current of the inverter, and designs closed-loop control parameters for single phase grid connected inverter.Thirdly, based on the traditional virtual capacitor control strategy, control strategy of feedback control and improved topology is proposed based on gridvoltage feed forward The working principle and control chart of two control strategies are given, and a detailed analysis is made, the size of the virtual capacitor is optimized, the selection principle of the closed loop parameters of the system is designed.Finally, the simulation model of single phase photovoltaic grid connected inverter is built by Matlab/Simulink simulation software, control strategy for traditional virtual capacitor, detection feedback control based on grid voltage feed forward and improved topology control strategy are carried out. Simulation results verify the feasibility and effectiveness of the proposed control strategy in this paper.