Protection Scheme Based on Energy Value and Morphological Feature of Incipient Fault Current for Inverter Dominated Islanded Microgrids

The fault ride through (FRT) control of inverter-based distributed generators (IBDGs) is quickly activated after a fault to limit the output current within 2 per unit. There is a phase jump phenomenon at the commencement of FRT control. However, the low fault current level and time-varying phase could make it difficult to guarantee the rapidity and the selectivity of islanded microgrid protection. In this paper, the transient characteristics of islanded microgrids are analyzed considering the influence of IBDG fault response and flexible network topology. The solution reveals the phase jump direction and magnitude difference between internal and external fault currents. Then, the energy value, the skewness value of directional morphological gradient, and peak polarity of incipient fault current are applied to formulate the protection criteria. The proposed protection scheme offers the following features: faulted phase selection capability, insensitivity to fault inception angle, adaptation to changes in the network topology, noise immunity with signal to noise ratio (SNR) down to 1dB, and low communication bandwidth requirements. The simulation results verify the effectiveness of proposed scheme for various fault conditions.