An impedance identification-based islanding detection method for droop control inverters based on RDFT and positive–negative notch filters

Droop control inverters are widely used because of their plug-and-play characteristics, no need for communication, and adaptability to weak power grids. However, because of the difficulty of islanding detection, after the grid is restored, drooping control inverters may cause security problems. In order to address this issue, this paper proposes an islanding detection method for droop control inverters based on impedance identification. By injecting current disturbance into common coupling points (PCC), the impedance is identified by the current response, and then the islanding can be determined by the impedance change. On the one hand, a signal extraction method based on positive–negative notch filters is proposed to reduce the content and impact on the power quality of the disturbance injection. On the other hand, this paper uses a signal processing method based on recursive discrete Fourier transform (RDFT), which can effectively reduce the computational burden. Moreover, the proposed method can eliminate the non-detection zone of the island detection. The experimental results verify the effectiveness of the proposed method.