A novel islanding method based on the alternate current disturbances for photovoltaic grid-connected inverters

This When the power generated by the distributed power generation system matches with the consumed power of the local loads, and the load phase angle is equal to the angle of the current disturbance, even if the islanding occurs, the voltage frequency at the point of the common coupling (PCC) always keeps in non-detecting zone (NDZ). A detection method based on the alternate current disturbance (ACD) is used to detect islanding. However, the disturbances of ACD method have a serious influence on the quality of output power and it is limited by the amount of total harmonic distortion (THD). Therefore, an novel islanding detection method based on the alternate current disturbances is proposed in this paper. The proposed method injected a different current distortion into current waveform in the adjacent cycle. The disturbance make the frequency of the voltage at the point of common coupling (PCC) shift up in the first cycle, and shift down in the next cycle. The islanding is detected by judging whether the error of the frequency at the PCC in adjacent cycle changes alternately in the form of the positive and negative signs. The proposed method is validated by simulation does in MATLAB platform. The results show that the novel method can identify islanding very well, and the injected disturbance have less impact on power quality.