Current injection for active islanding detection of electronically-interfaced distributed resources

This paper presents an active islanding detection method for electronically-interfaced distributed resource units at the distribution voltage level. The proposed method is based on injecting a disturbance signal into the system through either the direct axis (d-axis) or the quadrature axis (q-axis) current controllers of the interface voltage-sourced converter. Signal injection through the d-axis controller modulates the amplitude of the voltage at the point of common coupling (PCC), whereas signal injection through the q-axis controller causes a frequency deviation at PCC, under islanded conditions. Monitoring strategies to detect islanding are also presented for the proposed injection method. The feasibility of the proposed method is evaluated under the UL1741 anti-islanding test configuration. The studies reported in this paper are based on time-domain simulations in the PSCAD/EMTDC environment. The studies show that the proposed islanding detection method succeeds in detecting the islanding phenomenon as fast as 33.3 ms for the parameter setting of the test system, and always meets the two-second UL detection requirement. The paper also concludes that the proposed method has the salient feature of offering a potential application in a micro-grid scenario, where fast islanding detection and not necessarily the anti-islanding function is required.