Island detection method based on grid-connection point voltage characteristic frequency

The invention discloses an island detection method based on grid-connection point voltage characteristic frequency and belongs to the technical field of anti-island protection of a distributed power supply system. The method is characterized by, in a distributed grid-connection system with a double-fed fan being as a power supply, detecting frequency of grid-connection point voltage of the double-fed fan according to local electrical quantity information through an independent island detection device; once detecting that the grid-connection point voltage frequency is changed to be a constant non-power-frequency value, determining that island happens, carrying out island protection and guaranteeing that the island can be removed smoothly within 2 s; and starting rotor side control strategy switching by increasing grid-connection point current sudden change amount auxiliary criterion, setting slip angle speed [omega]s in the double closed loop control to be a fixed value, and changing the frequency of the exciting current, thereby effectively eliminating detection blind zone of the double-fed fan in synchronous speed operation, not being influenced by load fluctuation or short circuit trouble, and realizing good robustness; and the method can realize quick and effective island detection function and has engineering practice meaning.