An Islanding Detection Method for Microgrids Using Synchronized Small-AC-Signal Injection

Islanding detection is of great importance in microgrids with multiple parallel inverters, while active islanding detection methods based on impedance measurement using signal injection face the problem of interaction of injected signals among parallel inverters. This paper proposes an islanding detection method based on synchronized injection of small-AC- signal (SACS), in which the injected signals are synchronized with each other using power-frequency droop control and virtual impedance without communication or off-line operation. Compared to existing injection-based methods, the proposed method is advanced in high reliability as each inverter injects SACS in equal status, which enables local controllers to detect islanding on their own based on the calculated equivalent impedance, and the synchronization is not influenced by fundamental power sharing. Simulation and experiment results are provided to prove the effectiveness of the proposed method.