An Impedance-Based Islanding Detection Method for DC Microgrids with multiple DGs

The islanding detection of the DC microgrid is of great significance to its safe operation. Because electrical features such as frequency, phase, etc. are absent in the DC system, most of the islanding detection methods used in the AC system do not apply to the DC system. In the DC microgrid with multiple distributed generations (DGs), the existing active islanding detection methods have the risk of detection failure due to the dilution caused by asynchrony of the injected disturbances. To solve this problem, this paper proposes a new islanding detection method for DC microgrids with multiple DGs based on impedance detection. This method performs an injection organization to ensure that only one converter in the system injects the disturbance signal. Thereby, the dilution effect caused by the simultaneous injection of multiple machines can be avoided. The dynamic master role allocation mechanism is used to improve reliability. In addition, PR control is used to eliminate the influence of converters output impedance on impedance measurement. Then the complexity of the threshold setting has been simplified. Besides, with the establishment of a small-signal model of the DC microgrid, the selection of the favorable frequency of the disturbance signal is given. Simulation results prove that this method can quickly and accurately detect the islanding event in DC microgrids with multiple DGs.