Study On Control Method And Loss Analysis Of Dual-Frequency Single-Phase Photovoltaic Grid-Connected Inverter

The application of distributed photovoltaic power generation requires a large number of transformers and long-distance transmission lines,which leads to a non-negligible grid impedance and various background harmonics in the public grid,and the grid shows the characteristics of weak grid.The interaction between the weak grid and the grid-connected inverter will affect the grid-connected power quality,and even endanger the stable operation of the power generation system.Therefore,how to suppress the grid voltage distortion,ensure the stability and power quality of the distributed photovoltaic power generation system,and improve the efficiency of the grid-connected system are the key research issues of grid-connected inverter.In view of the above problems,this paper takes dual-frequency single-phase photovoltaic grid-connected inverter as the research object,studies its control method,and establishes a loss model to analyze its efficiency.The specific research work is summarized as follows:(1)The topology of the dual-frequency single-phase photovoltaic grid-connected inverter is determined,which includes boost circuit,power inverter and auxiliary converter.In addition,the principle of the feedforward switch ripple compensation control(FSRC)method to eliminate the grid current harmonics is briefly analyzed,which is also the core idea of the dual-frequency grid-connected inverter.(2)The control method of the dual-frequency single-phase photovoltaic grid-connected inverter is introduced,and the controller of the current inner loop in the power inverter and auxiliary converter is selected to improve the design,so as to improve the dual frequency inverter’s ability to suppress the low order harmonics of grid current,and further ensure the power quality.(3)Aiming at the problem of grid voltage distortion and grid impedance causing the grid current quality to degrade,a PCC voltage feedforward control method is given.By drawing the bode diagram,it shows that the dual-frequency inverter can effectively suppress the influence of the grid voltage distortion on the current quality,and the system has strong robust stability against the variation of grid impedance.(4)The loss calculation model of dual frequency grid connected system is established,which shows that the dual frequency photovoltaic grid-connected inverter has the advantages of low loss and high efficiency.(5)A 1.5 kW dual-frequency single-phase photovoltaic grid-connected inverter simulation model is built based on Matlab/Simulink,and a dual-frequency grid-connected inverter experimental platform is designed based on the STM32F407ZGT6 control chip.The simulation and experimental results show that the dual frequency inverter with PCC voltage feedforward control,FSRC control and improved controller has the advantages of strong stability,less harmonic content of grid current and high power quality.