Frequency Based Islanding Detection Methods in Power Electronic Converters

Frequency based methods developed to detect an islanding condition in modern power grid structures have been discussed. The condition may occur in power grid lines to which additional energy sources with power electronic converters have been connected such as solar panels or wind turbines. It is a hazardous operating state for grid workers and devices connected to the islanded part of the grid. Such a state results from the inability to control amplitude and frequency of basic harmonic of the grid voltage. An islanding problem in a power grid with additional small energy sources has been discussed. A basic passive and active islanding detection method have been presented and compared with known frequency based algorithms, namely active frequency drift and active frequency drift with a positive feedback algorithm. Finally, a laboratory test of the proposed islanding detection methods in a three- -phase grid with an AC-DC converter has been conducted. To demonstrate differences between the tested methods, total harmonic distortion injected into the output converter current and detection time of islanding state have been measured.