Analysis And Research On Island Detection Method Of Distributed Photovoltaic Grid-connected System

Based on the island detection of distributed photovoltaic grid-connected power generation systems,this paper first introduces the development and current status of grid-connected photovoltaic power generation and island detection at home and abroad,explains the purpose and significance of island detection,and summarizes the classification and characteristics of island detection methods.The principle,detection standard and validity judgment of the island effect are introduced in detail.Then,based on the current research results of photovoltaic grid-connected systems at home and abroad,the common islanding detection methods are compared and analyzed in depth,and the characteristics and advantages and disadvantages of each detection method are discussed.In recent years,discussions on island detection methods have been endless.Experts and scholars from various countries have proposed a variety of optimization schemes for photovoltaic island detection,but there are still problems such as detection blind spots,insufficient detection timeliness,and large impact on power quality.This article proposes optimization schemes from two approaches,active detection and passive detection.For the active detection method,the most representative frequency offset method is selected for research.The active frequency offset detection method(AFD)and the active frequency offset detection method(AFDPF)with positive feedback are introduced.The detection of the two methods is analyzed in detail.Principle and performance,and an improved piecewise AFDPF detection method is proposed.The AFDPF algorithm is optimized by adding a sign function and a piecewise function to reduce the harmonic content and improve the detection efficiency.According to the passive detection method,the over/under voltage(O/UV)method is improved.The voltage at the common coupling point is filtered,and the AC voltage signal is converted into a more accurate island detection signal.Detect slow defects and detect islands during power matching.In this paper,MATLAB/Simulink simulation software is used to carry out simulation experiments on the two proposed methods.The simulation models of single-phase photovoltaic grid-connected system and three-phase photovoltaic grid-connected system are established respectively,and the rationality and effectiveness of the proposed method are verified.