Research On Distribution Photovoltaic Power Generator And Its Leakage Current Reduction Methods

Energy shortage and environmental pollution has been a hot issue all over the world in the 21 st century. Among these new energy sources, the solar energy, which is widely distributed, abundant, unlimited, and no greenhouse gases to produce, charms people particularly. With the rapid development of distributed photovoltaic( PV) system, photovoltaic grid-connected inverter has been researching and applying more and more commonly. Compared with the classical power frequency transformer or high frequency transformer photovoltaic gird-connected systems, transformerless gird-connected photovoltaic inverter has the characteristics of small size and high efficiency. With the high-speed development of power electronic devices, more and more research and application has been set in recent years. Because there is no electrical isolation transformer, solar photovoltaic panels are inevitable existence of parasitic capacitance, leading the isolation type photovoltaic grid inverter producing leakage current. Leakage current is a huge security risk which greatly restricts the application of transformerless gird-connected photovoltaic systems. Therefore the study of how to inhibit the leakage current is of great significance. This article researches the transformerless grid-connected photovoltaic inverters mainly in the following four aspects.(1) The works of distributed PV grid-connected inverter is introduced and the causes of the leakage current analyzed. The variable common-mode voltage value acts on parasitic capacitance that cause common-mode current, also called leakage current. The basic method to eliminate is to keep common-mode voltage in variable.(2) Several new types of inverters which can inhibit common-mode current are analyzed from structure and efficiency and simulated with Matlab software. Conclusion that HERIC, FBDC, H6 types new inverters can effectively reduce leakage current while H5 type is economical and NPC type is suited for three-phase inverter is drew.(3) Comparing the characters of different controllers on a typical transformless grid-connected inverter. PR control strategy is good for output of current.(4) An accurate model of photovoltaic cells is established and used to achieve a Maximum Power Point Tracking model which can be a reference for engineering.