Unit Protection of Tapped Line DC Microgrid

Abstract

DC microgrids are attractive options for being more efficient and less complex than ac microgrids. Several protection methods exist for ring main and radial dc microgrid architecture, but the development of protection techniques for tapped line-based dc microgrids is still in the beginning stage. Usually, the loads and distributed energy resources (DERs) are tapped at any section of the line in the microgrid. When there is no communication link from the tapped line to any bus in the microgrid, the existing unit protection schemes fail to identify the fault in the tapped line-based medium-voltage direct current (MVDC) microgrid. In that case, the existing unit protection scheme fails to identify the fault in the tapped line-based MVDC microgrid. Therefore, this article proposes a new unit protection scheme for the tapped line MVDC system based on the superimposed resistance. The proposed method identifies the tapping status using the prefault current data. The technique is robust during load changes and power generation variation at the tapping station. The proposed scheme is validated using a two-bus tapped dc microgrid for distinct fault scenarios like high-resistance fault, varying fault location, and different modes of distributed generation operation under MATLAB/Simulink environment. Also, the performance of the proposed scheme is verified on a lab-implemented dc microgrid hardware bed and tested for different types of fault scenarios.