Study On A New Method For Island Detection In Photovoltaic Grid-connected Power Generation System

With the increasingly serious problems of energy depletion and environmental pollution,the efficient development of clean energy has become a trend.Solar photovoltaic power generation is one of the important forms of clean energy utilization.Solar photovoltaic grid-connected power generation is the main way of solar energy utilization,but the grid connection of large-scale photovoltaic power supply will inevitably affect the power system itself and bring many problems to the stable operation of the system.Besides considering the control and detection of normal system,a special fault in photovoltaic grid-connected system is islanding fault,and the detection of isolated island fault has become a hot spot for experts and scholars at home and abroad at present.This paper focuses on photovoltaic grid connection The island detection method is studied in depth.This paper introduces the existing island detection methods,and provides a reference for further research.By analyzing the relationship between the topology of photovoltaic grid-connected power generation system and the fault characteristics of isolated islands,a three-phase single-stage photovoltaic grid-connected power generation system based on grid voltage directional vector control was built in PSCAD simulation software.The veracity of the model is verified and the model is taken as the research object of simulation.In this paper,the generation mechanism and power matching of islanding effect in photovoltaic grid-connected power generation systerm are introduced.Aiming at the shortcomings of several traditional detection methods,a method of island detection based on harmonic impedance fault component is proposed in this paper.By comparing the change of the system's equivalent impedance caused by the change of the topological structure between the normal grid-connected operation and the isolated island operation,the characteristic frequency,voltage and current signals at the common coupling point are extracted.According to the difference of harmonic impedance sequence component of characteristic frequency before and after fault,the occurrence of islanding is judged.In this paper,an improved islanding detection method based on the fundamental component of integrated impedance is proposed to solve the problem that the fault component is small in the harmonic impedance method,and the variation of harmonic impedance caused by the small and medium disturbance in the system leads to the misjudgment of the harmonic impedance.According to the variation characteristics of voltage and current signals related to the transient characteristics of islanding fault,the fundamental frequency signals of voltage and current at common coupling points are extracted,and according to the difference of integrated impedance caused by the change of electric volume before and after the islanding,the voltage-current fundamental frequency signals are extracted,the occurrence of the islanding is judged.The above two islanding detection methods are simulated to verify the correctness of the detection method,and have the advantages of faster detection speed and no detection blind area,and will not affect the output power quality of the inverter,and the results show that the proposed method has the advantages of fast detection speed and non-detection blind area,and can not affect the output power quality of the inverter.It provides a theoretical basis for island detection in photovoltaic grid-connected power generation system.