A Positive/Negative Voltage Sequence Droop-Based Differential Protection Scheme for Islanded Microgrids With Inverter-Based DG

Inverter-interfaced distributed generators (IIDGs) embedded in microgrids inject limited fault currents, thus imposing a challenge on the protection of the islanded microgrid. This article proposes a novel protection scheme that injects a negative phase sequence (NPS) current component from the IIDG interface control during fault conditions to facilitate fault detection and isolation. This injection is accomplished by augmenting the traditional droop controller of IIDG with a novel positive phase sequence (PPS) voltage versus NPS voltage ($V_{\text{PPS}}-V_{\text{NPS}}$) droop, designed to inject negative sequence current during fault conditions only. Differential NPS current relays are distributed at the line ends to provide fault detection and isolation. The effectiveness of the suggested protection algorithm has been tested and validated using PSCAD/EMTDC simulation software, which considers various fault conditions, such as different fault types, locations, and resistance. The suggested droop-based protection algorithm eradicates the need for a dedicated fault detection scheme and can accurately distinguish faulty and nonfaulty conditions.