Active islanding detection technique for inverter-based microgrids using optimized negative sequence disturbance injection

Deploying grid ancillary services in distributed energy resources (DERs) can interfere with islanding detection techniques (IDTs), potentially enlarging their non-detection zone. Several active IDTs have been accordingly presented for inverter-based DERs in the literature; however, they often suffer from power quality (PQ) degradation during grid-connected (GC) operations. To address this issue in inverter-based microgrids, this paper proposes an active IDT, employing negative sequence disturbance (NSD) injection into the DER reference current. The injected disturbance leverages feedback from filtered negative sequence voltage (NSV) at the DER terminal. Optimum filter parameters in the feedback loop are analytically chosen to enhance stability in GC mode and augment instability after island formation. To this end, this proposed IDT is structured so that the NSD is only triggered by grid events and rapidly decays to zero, mitigating PQ issues in GC operation. At the same time, the induced instability causes a sharp rise in NSD upon islanding, settling at a limited value. This disturbance raises the NSV at the DER terminal, which its increase for a given time delay concludes an islanding detection. The efficacy of the proposed IDT is corroborated through extensive simulations on the PSCAD platform for photovoltaic (PV)-based microgrids, adhering to the IEEE standard 1547.1-2020 test procedure with grid ancillary services. The proposed method successfully detects stringent single- and multi-PV islanding scenarios within 400 ms. Due to the simple structure and straightforward implementation, this technique can be adopted for future inverter-based technologies.