A Study on Operation Method of Protection Coordination in 5kV MV-LVDC Off-grid Micro-grid System

Recently, demands on MVDC distribution system is being significantly increased due to interconnection of renewable energy sources, expansion of DC load and high quality and reliability of the power supply system etc., while commercialization of facilities for MVDC is yet in early stage. Accordingly, demonstration projects on applying existing AC devices and cables to MVDC distribution system are being carried out. However, the protection on high-cost facilities such as converters and cables may not be reliable in the event of fault, and then operation method of protection coordination for MV-LVDC micro grid(MG) system is being required. For the purpose of stable operation of the 5kV MV-LVDC micro-grid, this paper proposes operation methods of protection devices depending on scenarios, such as faults on the MVDC line, LVDC line, or customer load. And also, a modeling of 5kV MV-LVDC MG system, which is composed of PV system, ESS, MVDC cable, DC/DC converter, DC/AC inverter, protection devices etc., is performed using PSCAD/EMTDC S/W. From the simulation results based on the proposed modeling and operation method of protection devices, it is confirmed that this paper is useful tool to perform the proper protection coordination. © 2022 Korean Institute of Electrical Engineers. All rights reserved.