A Novel Islanding Detection Technique Based on Positive-Feedback Negative Sequence Current Injection

This article proposes a new active anti-islanding technique to detect unintentional islanding with high speed and reliability. In grid-connected mode, the controller has no influence on the power system. When the grid is disconnected, the inverter injects negative sequence current in a positive feedback loop, and causes the output negative sequence voltage to increase to a threshold value that causes the inverter to stop operating. The proposed method is nonintrusive and does not cause disturbance to the system in grid-connected mode. The method is tested using PSCAD simulation software, and using controller hardware-in-the-loop (C-HIL) using the physical control board of the inverter. The inverter considered in this article is a photovoltaic inverter with 840-kW rated power. Optimization of the parameters of the proposed control, as well as small signal stability analysis in grid-connected mode are presented. Verification results show that the controller can detect unintentional islands and stop the inverter within 500 ms.