Active Slip Frequency Based Islanding Detection Technique for Grid-Tied Inverters

In this article, an islanding detection technique (IDT) is proposed based on applying positive feedback of wide area measurement based slip frequency at the inverter reactive power control loop. The classical Q--f droop characteristic based IDT is affected due to variations in load and active power mismatch (APM) conditions that may exist during islanding condition. To overcome these issues, an adaptive reactive power injection based IDT is proposed. Adaptiveness in the proposed method is achieved by considering the gain of the reactive power control loop as a product of rate of change of susceptance with respect to frequency seen at the inverter terminals, square of per unit point of common coupling voltage and slip frequency, which is the difference between distribution generator frequency and a reference substation bus frequency. The application of slip frequency as a positive feedback parameter injects negligible reactive power during grid side frequency disturbances and also associates with under frequency and over frequency ride through requirements. The method is least effected by load quality factor variations and APM conditions. The IDT is able to detect islanding conditions with a negligible non detection zone. Real time simulation studies are performed using dSPACE DS1104 real time controller and RTDS/RSCAD.