A novel integrated islanding detection method based on adaptive accelerating frequency drift

A adaptive accelerating frequency drift (AAFD) method combined with the negative impulse current amplitude disturbance is proposed for the islanding detection of grid connected photovoltaic (PV) system. Based on the number of continuing frequency change towards some direction for the voltage at the point of common coupling (PCC), the positive feedback frequency drift coefficient is adaptive subsection adjusted to accelerate shifting the frequency. Furthermore, if the frequency is not out-of-limit when the change number is more than 12, then the negative impulse current amplitude disturbance which continues two power frequency periods is adopted to fire under-voltage protection (UVP) to realize the islanding detection. Matlab simulation results show that the proposed method comprehensively utilizes and overcomes the shortcomings of traditional active frequency drift (AFD) and the current disturbing method so that it can make the PV system disconnected from the grid system before high-speed auto reclosing with limited harmonics and reduced non-detection zone.