Mitigating low fault current in microgrids through renewables-battery hybrid units

One of the major problems with inverter-based distributed generation (IBDG) compared to synchronous gen-erators, is the little fault current contribution during fault condition in islanded mode of operation. Particularly, the increased penetration of IBDGs such as renewable energy sources (RES) into the microgrid (MG) has a substantial impact, as it would lower the fault current level; such diminished fault current induces mal-trip and fail to trip of protective relays causing problems in fault detection and isolation and consequently degrades the MG protection. To tackle this issue, this paper proposes an adaptive protection scheme that considers RES, Battery Energy Storage System (BESS), Hybrid units in the MG. The proposed scheme applies an internal cooperation strategy between RES and BESS to ensure reliable output power. Then, a power flow-based fault analysis is performed to determine the fault current paths. A fault current zone (FCZ) is formed out of the IBDGs that are found to be on the observed fault current paths and an optimal residual capacity is determined for the BESS units within FCZ; the optimization is formulated as a nonlinear program for maximizing the residual ca-pacity of the BESS unit. Validation of the proposed scheme is carried out through simulation of the IEEE 33 bus systems. The simulation results confirm the effectiveness of the proposed protection scheme and its superiority to competing approaches in the literature.