An Active Protection Scheme for Microgrids Based on the Harmonic Injection

Inverter Interfaced Distributed Generation brings major challenges to the protection of microgrids, the traditional passive fault observation that does not use IIDG controllability, and the protection scheme based on the premise that the fault and non-fault characteristics are significantly different are no longer applicable. This paper proposes an active protection scheme for microgrid based on harmonic energy injection. The IIDG interface electrical signals are used for fault detection. In case of fault, the IIDG inverter started the harmonic energy injection function based on equivalent impedance modulation. The adjacent IIDG injected different frequencies' harmonic energy. The closer the fault point was to IIDG, the greater the harmonic energy injected. The scheme collects the fault harmonic current in the relay, and sets the protection criterion based on the ratio of the detected harmonic currents of different IIDGs. The minimum range of fault clearing is realized by blocking logic. A harmonic current ratio relay is designed for the protection scheme. The proposed active protection scheme was suitable for microgrids with multiple IIDGs, and can meet both connected and island operation mode. A benchmark radial system practically under use in Canada was established in PSCAD/EMTDC, and the effectiveness of the scheme under different fault conditions was verified through simulation research.