The probability of islanding of grid-connected distributed generators is relatively large on the user side. Taking the user safety and power quality into account

the islanding mode should be detected quickly and accurately. An active islanding detection scheme based on 20 Hz low-frequency power supply injection is proposed. The 20 Hz component which is equivalent to zero sequence component is injected into the 380 V system and islanding is identified by the change characteristics of the 20 Hz component. The composition and detection principle of the proposed scheme

parameters selection and its influence on power quality are described and analyzed in detail. MATLAB is applied in the modeling and simulation

and correctness of the analysis is verified by simulation results. The identification criterion for the island mode based on comparison of the absolute value is proposed and realized in a grid-connected interface device. Finally

the scheme is experimentally verified in a small rooftop distributed photovoltaic generation project.