Research on a novel islanding detection for micro-grid connected inverters

When the grid fails, the micro-grid systems can use the active frequency drift (AFD) method to detect the islanding phenomenon. However, if the current disturbance angle equals the load angle, the AFD method fails. As for the problem, this paper discusses a novel current-disturbing method in the positive half voltage period. That is, in the positive half voltage period, disturbing the current frequency, and in the negative half voltage period, keeping current frequency in sync with the voltage frequency. Once the islanding occurs, the frequency of the point of common coupling (PCC) will be changed owing to the change of the output current frequency. The islanding can be identified by judging whether the positive and negative half voltage period changes alternately in the form of the positive and negative signs. The simulation results show that the proposed detection method can not only narrow the range of non-detecting zone (NDZ), but also is effective and practical.