Research of Improved Active Frequency Drift with Positive Feedback Islanding Detection Method

摘要

Nowadays, the active frequency drift with positive feedback (AFDPF) islanding detection method which can solve the islanding of photovoltaic (PV) systems is widely used. However, the traditional AFDPF method may cause some problems such as the missing detection of islanding and the extension of detection time when the power grid fails and the loads' natures are different. In order to solve the problems, the essay proposes an improved AFDPF islanding detection method. This method introduces sign-function before the disturbance signal cf_0 (initial chopping fraction). Through this way, we can make correction for cf_0 so as to overcome the problems mentioned above. To verify the validity of the method, an example is utilized. The simulation analysis of the example indicates that after introducing sign-function before cf_0, the islanding can be detected effectively under different loads conditions, in addition, the detection time can be reduced a lot and the grid-connected current waveform is quite good. So by this method, both the detection reliability and the detection efficiency can be improved greatly.