An improved islanding detection method for grid-connected photovoltaic inverters

There is significant negative impact due to an unintended islanding supported in DG systems, resulting in developing passive and active methods to detect and eliminate islands. Many active techniques have been directed towards frequency shift method, in which active frequency drift (AFD) method is classical. Active frequency drift with pulsation chopping fraction (AFDPCF) is a recently proposed method to improve the AFD method. However, both methods have large non-detection zone and the chopping fraction may extend the run-on time and fail to detect islanding operation. The modified AFDPCF method proposed in this paper monitors the frequency tendency first and then decides the suitable chopping fraction, ensuring fast and effective anti-islanding operation. The simulation results show that the proposed algorithm is capable of detecting the islanding condition correctly, with smaller non-detection zone and less harmonics.