A Comprehensive Digital Protection Scheme for Low-Voltage Microgrids with Inverter-Based and Conventional Distributed Generations

Microgrid (MG) protection is one of the main challenges in proliferation of microgrids. Due to limited fault current feeding of inverter-based distributed generations (DGs), in islanded operation of MG, protection problems become more complicated; and, therefore, conventional protection strategies cannot be applied. Hence, new protection methods that are applicable in islanded and grid-connected modes of operation are necessary. In this paper, a comprehensive digital-relay based protection is introduced for the protection of MGs. The proposed method includes protection of lines, distributed generations, and the point of common coupling. The structure and graphical schematic of the proposed digital relays are also presented. The proposed method is independent of the MG operation mode and benefits from single-phase tripping. In this method, due to fault isolation from both sides of a line, downstream loads and DGs can operate after fault clearance. To demonstrate the effectiveness of the proposed protection method, numerous simulations are carried out on an MG test system in the PSCAD/EMTDC environment.