Methods and Techniques For The Protection of Microgrid Systems

Several challenges exist when designing a suitable protection scheme for a microgrid system. Bi-directional current flow and limited short circuit current are significant problems for traditional low-voltage protection schemes. Dynamic changes in the microgrid’s structure exacerbate these issues. High penetration of inverter-based resources (IBRs) limits the short circuit capacity of a microgrid system. During islanded-mode operation, the fault current may not reach the level required to trip the circuit breaker. This need not be the case. It was determined that distributed energy resources (DERs) can be leveraged to support rather than degrade relay operation. To study these challenges for the microgrid, a hybrid AC/DC microgrid setup is proposed to show the different modes of operation and the necessary of DER to contribute to the AC side during the fault condition. As, normally, DER can be used to feed some loads at the DC side, but when the fault occurs, the need for a static transfer switch due to its ultra-fast switching is important to disconnect the DC loads and allow DER to only help the relays to reach their settings and isolate the fault appropriately. This paper presents simulations of several microgrid case studies representing fault conditions under both grid-connected and islanded modes and proposes.