An Improved Active Frequency Drift islanding Detection Method with Lower Total Harmonic Distortion

Anti-islanding detection is a mandatory function for grid-connected inverters to protect the safety of electrical equipments and maintenance personnel. A desired islanding detection method not only has shorter island detection time and smaller nondetection zone (NDZ), it is also required to have less side impact on power quality. As a commonly used anti-islanding method, the active frequency drift (AFD) method can effectively detect islanding with a smaller NDZ at the expense of poor grid-injected current with increased total harmonic distortion (THD). In this paper, an improved AFD anti-islanding detection method is proposed to relieve the side effect on the power quality. Compared with the classic AFD method, the proposed method generates 90% less THD. In other words, the proposed method has shorter island detection time and improved NDZ compared with the classic AFD method when they have the same THD. The performance of the proposed method is derived analytically and verified by Matlab simulation. A prototype is building in the lab now and the experimental results will be shown in the full paper.