Fault Protection Scheme for DC Nanogrids Based on the Coordination of Fault-Insensitive Power Electronic Interfaces and Contactors

DC microgrids can lead to a better integration of Distributed Energy Resources (DERs) than AC microgrids. DC nanogrids typically include a number of DERs in close proximity. Various power balance and energy management schemes have been developed, but fault protection still remains an issue for DC nanogrids. This paper discusses the realization of a fault detection and isolation scheme based on the coordination of fault-insensitive power electronic interfaces and low-cost contactors. It is based on “local branch current sensing” and peer-to-peer communication to identify which segment of the DC nanogrid is faulted and which contactor should open. In order to employ low cost/current contactors, following the detection of a fault, the DERs should decrease the injected current to a value low enough for safe action of the contactors. For that, a fault-insensitive current controller power electronics interface as discussed in this paper is needed. Experimental results with power electronics interfaces operating with DC Bus Signaling (DBS) and a CAN communication scheme are presented.