1.合肥工业大学电气与自动化工程学院，安徽省合肥市 230009;2.阳光电源股份有限公司，安徽省合肥市 230088
1.School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China;2.Sungrow Power Supply Co., Ltd., Hefei 230088, China
This work is supported by National Key R&D Program of China (No. 2016YFB0900300) and National Natural Science Foundation of China (No. 51677049).
In order to ensure the safety and power quality, the distributed generation system based on grid-connected inverters needs islanding detection function. The conventional islanding detection methods are not suitable for the grid-connected inverter with droop control, and the existing islanding detection methods designed for grid-connected inverters with droop control have to change the droop characteristics and exist non-detection zone. To solve the problems above, this paper proposes an islanding detection method for the grid-connected inverter with droop control based on impedance identification. The method injects voltage disturbance at the point of common coupling, identifies the impedance by voltage and current disturbance signals, and then decides whether the islanding effect occurs according to the impedance variation. In order to improve the detection sensitivity, the harmonic disturbance injection is adopted to amplify the differences of characteristic parameters before and after islanding. In addition, the disturbance signals are extracted by recursive discrete Fourier transform, which improves the accuracy and timeliness of impedance identification. The experimental results verify the effectiveness of the proposed method.