Evaluation of current injection as an active islanding detection method, under the UL1741 standard configuration

This thesis proposes an islanding detection method for electronically-interfaced distributed generation units, and evaluates it under the UL1741 anti-islanding test configuration. The proposed method injects a disturbance signal into the system through either the direct axis (d-axis) or the quadrature axis (q-axis) current controllers of the interface converter. This thesis analyzes the effects of both d-axis and q-axis current injections on the voltage waveform at the point of common coupling upon islanding occurrence. Signal injection through the d-axis controller causes voltage amplitude modulation, whereas signal injection through the q-axis controller causes frequency deviation from the preislanding value of 60 (Hz). Based on this analysis, different monitoring strategies are proposed to obtain an islanding indicator. PSCAD/EMTDC simulations indicate that disturbance injection by the q-axis controller provides a reliable islanding indicator. This thesis concludes that the proposed method satisfies the UL1741 test requirements.