Wavelet packet-based passive islanding detection method for grid connected photovoltaic inverters

In this paper, a new passive islanding detection method for grid-connected photovoltaic inverters is proposed. The proposed method is based on extracting signatures from the high frequency components of voltage at the point of common coupling (PCC), which occur after an islanding condition. These high frequency components contain signature information capable of identifying the islanding condition. The PCC voltage is measured and its high frequency sub-band contents are extracted using wavelet packet transform (WPT). This characterization helps to provide enough information to efficiently detect and discriminate the effect of load switching disturbances and grid voltage distortions from islanding conditions. The effectiveness of the proposed method is tested in simulation of a grid-connected inverter system. The simulation results, carried out by Matlab/Simulink are used to validate the performance of the proposed method. The results demonstrate that the proposed method can detected within one cycle (20 ms), even with small non-detection zone and can discriminate between islanding and other events in the system, as load switching disturbances and grid voltage distortions.