Research On The Anti-islanding Detection Methods Of Single-phase PV Grid-connected Power Generation System

At present, energy depletion and environmental pollution problems have became challenging problems which humanity must face. Under these circumstances, photovoltaic power generation systems have become a global focus on supporting the development of strategic industries. Anti-islanding detection is one of the key part in the whole grid-connected PV systems, and it directly relates to the reliability and power quality of the PV grid-connected power generation systems. Therefore the research is of great significance.In this paper, firstly, the overall structure of single-phase grid-connected PV systems is introduced, including inverter type, inverter topology, filtering circuit topology selection, and the paper also gives the diagram and equivalent model of the single-phase grid-connected PV systems mentioned above. Secondly, the paper introduces the basic principle of anti-islanding detection, both domestic and international anti-islanding detection standards and commonly used anti-islanding detection methods. Then a novel anti-islanding detection method based on injecting the even-order harmonics is proposed, and it fully describes the principle of detection method, the analysis of the range of the even harmonics and filtering methods. It is also verified by building the simulation model of the single-phase grid-connected PV system in Matlab/Simulink under different load circumstances. The simulation result shows that it has a fast detection speed, none NDZ, good robustness, small impact on the grid power quality and can also be applied to the anti-islanding detection problems for multiple inverters parallel operating systems. Moreover, the paper proposes an improved frequency shift active anti-islanding detection method and give the detailed description and analysis of it. The method has a lower THD of current waveform and smaller NDZ compared to the current waveform of traditional AFD anti-islanding detection method. Meanwhile, the effect on the output current waveform of the improved method is verified by simulation. Finally, the paper summarizes the whole work, and points out the direction of future research.