Research On The Three-phase Non-isolated Grid-connected Inverter And The Technology Islanding Detection

Photovoltaic power generation is one of the most important forms of solar energy utilization.When photovoltaic power generation system is connected to the power grid,for the stable operation of the power grid,the safety of electrical equipment and personnel,there are a lot of problems to be studied,the suppression of common mode voltage and the detection of isolated island are included.This paper first introduced the background and significance of photovoltaic power generation technology.At the same time,the current development of photovoltaic power generation and the classification of topology of grid connected inverters,the concept and suppression of common mode voltage,and the concepts,hazards and detection methods of isolated islands are reviewed.The main research work of this paper is introduced,included the following contents.(1)The principle of the main circuit of the three-phase H7 voltage source photovoltaic grid connected inverter is introduced,the problem of common mode voltage suppression and closed loop design are studied.When the space vector pulse width modulation(SVPWM)is zero vector,the common mode voltage is suppressed by controlling the switching of the additional switch on the DC bus in the main circuit topology of the three-phase H7 voltage source photovoltaic grid connected inverter.The mathematical modeling and closed loop dynamic design are carried out in the synchronous rotating coordinate system to ensure the system can run steadily.(2)The problem of isolated island detection is studied.The basic principle and judging rules of the sinusoidal low frequency phase disturbance(ALFD)method are introduced.On this basis,The implementation strategy of ALFD method in three-phase H7 voltage source grid connected inverter is studied in depth.(3)The software and hardware system of the three-phase H7 voltage source photovoltaic grid connected inverter are designed.Including the type selection of the main circuit,the control circuit and the design of the drive circuit,the design of the interrupt program,and the principle and control logic of the SVPWM algorithm.(4)In view of the main content of the paper,software and hardware experiment platform are built.The simulation results show that when the zero vector is acted,thecommon mode voltage can be effectively suppressed by controlling the on-off of the additional switches on the DC bus in the main circuit topology,and it is feasible to use the ALFD method in three-phase H7 voltage source grid connected inverter to quickly detect the isolated island.At the same time,both the simulation and the experimental results show that the system stability design of the three-phase H7 voltage source grid connected inverter is reasonable.