An Islanding Detection Method for Grid-Connected Inverter of Distributed Renewable Generation System

This study proposes an islanding detection method for use of grid-connected inverter of distributed renewable generation system. The proposed method is based on two indices: the rate of change of voltage (ROCOV) and the rate of change of frequency (ROCOF). When an inverter is grid-connected, the ROCOV and ROCOF are lower than the threshold values. In contrast, as an islanding occurs, the ROCOV or ROCOF becomes much higher than the threshold values. Detection systems monitor the terminal voltage at the grid-connected point to calculate ROCOV and ROCOF, and issue an operating signal when the value and duration of ROCOV or ROCOF exceed a given threshold. In this study, experiments are conducted to illustrate the principles of the proposed technique for a prototype grid-connected inverter. The test results show that the proposed method is reliable, economical, and easy to implement for islanding detection of grid-connected inverter.