Research On Island Detection Based On Active Frequency Drift

In order to cope with global climate change,environmental pollution,energy shortage and other problems,the use of renewable and clean energy has become a hot spot.Distributed power generation system,represented by photovoltaic power generation system,plays an important role in helping to achieve the "double carbon" goal of "carbon neutrality,carbon peak",accounting for an increasing proportion in the power grid.It is indispensable to detect the island phenomenon of the grid-connected independent power inverter.Anti-island protection is a necessary function,which can effectively improve the security and reliability of system operation.The key of island detection is to find the difference of electricity quantity between the grid-connected state and off-grid state so as to detect the possible island state quickly.In the method of Active Frequency Drift(AFD),the grid-connected current frequency is offset by injecting small disturbance into the grid-connected inverter,and the cumulative frequency offset superposition appears in the island state,and finally exceeds the threshold set by the grid-connected standard of the inverter to achieve island detection.In this paper,the indicators of AFD and Active Frequency Drift with Positive Feedback(AFDPF)are analyzed in detail,including island detection speed,detection blind area and the influence on power quality during normal grid connection.On this basis,a kind of island detection algorithm with adaptive functions has been proposed,which can determine island more accurately,reduce disturbance in the normal state,increase disturbance quickly in the island state,further reduce the influence to power grid,improve test rapidity,reduce the failure rate of detection,so as to realize the intelligent detection.In addition,taking the parallel operation of two grid-connected inverters as an example,based on the island detection dilution effect of multiple inverters running in parallel,the island detection effect of different algorithms applied to the parallel combination under active frequency drift is deeply compared and analyzed.Based on Matlab/Simulink platform,AFD,AFDPF and AFDPF control algorithm with adaptive function are discussed and verified by simulation.The results show that:The proposed algorithm and the optimal combination can improve the overall effect of island detection and meet the requirements of multiple inverters connected to the grid in parallel.