Research And Design Of String-type Non-isolated Photovoltaic Grid-connected Inverter

The consumption of earth's resources has caused serious environmental problems.The development of clean energy to replace traditional energy is an urgent development trend in today's society.The string-connected grid-connected inverter is one of the hotspots of solar energy utilization.It can convert the DC power generated by the photovoltaic panel into AC power and merge it into the power grid.As a direct factor affecting the stability of the power grid,the grid-connected inverter is particularly important to improve its power generation quality and conversion efficiency.Firstly,This paper established a mathematical model of the solar cell,analyzed the output characteristics of the battery when the temperature and light intensity were different,and proposed a variable step conductance increment method and modeling simulation to solve the Insufficient stability of the traditional conductivity increment method for tracking the maximum power point and the speed;the interleaved parallel dual Boost converter used in the previous stage circuit is designed,the topology structure and output current ripple were analyzed and modeled,and it was verified that it can basically eliminate the input current ripple and has high stability;the latter stage circuit adopted H6 inverter bridge to conduct theoretical research and modeling on its Topological structure,working mode and common mode leakage current for theoretical research and modeling simulation;verified that it can effectively suppress common mode leakage current;analyzed the principles and advantages of commonly used current control technology,designed Quasi-proportional resonance control and modeling and simulation to realize the tracking of the grid current without static errors,further improving the output power qualityFinally,designed the system hardware main circuit and peripheral circuits,completed the parameter calculation and component selection,and designed the single-phase string-type non-isolated photovoltaic grid-connected inverter with TMS320F28335 digital signal processor as the control core.Through software programming to achieve control algorithms and digital phase-locked loops,etc,builded an experimental platform for grid-connected experiments.It is verified that the output current of the inverter is at the same frequency as the grid voltage,current total harmonic is 3.5%.