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The active frequency drift (AFD) method is an effective method to detect islanding in grid-connected photovoltaic systems. However, it has some inherent drawbacks, such as generating higher harmonics. In order to reduce the harmonics and non-detection zone (NDZ), various improved AFD methods have been proposed, but they still suffer from high harmonics and reduced detection speed. To overcome these limitations, this paper proposes an innovative islanding detection technique based on AFD. Analysis reveals that the proposed method reduces harmonics by 68% compared to conventional AFD and has a larger chopping factor. Therefore, this technique offers several distinct advantages, including accelerated detection speed, reduced NDZ and harm caused by disturbances, and improved power quality. Furthermore, to verify the harmonic impact of this proposed islanding detection method, simulations and analyses are conducted using simulation software of Matlab/Simulink. An experimental prototype is set up in Laboratory. The simulation and experimental results demonstrate the superiority of the proposed method.

Island will not only lead a damaging to the equipment of the power system, serious when, may appear a series of problems like threatening the safety of the maintenance personnel of the power system. So the grid-connected Photovoltaic power generation system must have the function of detecting the islanding in all the time to ensure if the gird is working. The traditional AFD's detecting effects are different under different kinds of loads, it's better for the impedance load, but it brings a high THD. Although researchers proposed the improved AFDs based on the feedback adjustment or periodic disturbance which could reduce the THD, but they slow down the detecting speed at the same time. In view of this, this paper proposes a new active island detection method which adopts a novel disturbing way with low THD, and the detection effects are better than the traditional AFD under RLC impedance load. The non-detection zone is smaller and the detecting speed is faster, better yet, the THD injecting to the grid is lower, it has a practical value. In this paper, Matlab/Simulink simulation experiment shows that the proposed method is better than the traditional AFD at reducing THD, improving the detecting speed, and reducing the non-detection zone.