Fault current analysis for grid-connected and Islanded microgrid modes

Effective management of Distributed Energy Resources (DERs) becomes a formidable task with an increasing penetration at the distribution level. One of the proposed methods to integrate DERs in an electric grid is through the implementation of microgrids. A microgrid is a small Medium/ Low voltage network, comprised of several DERs and loads having a combined effect of a load or a generation source. In case of a fault in the utility grid, a microgrid can shift from a grid-connected mode to an island mode of operation. In this paper, we have analyzed the transient behavior of a microgrid using MATLAB Simulink's SimPowerSystems. The microgrid model is based on a standard distribution network with several renewable energy based DERs including solar, wind and a biodiesel generation plant. Three types of fault are simulated in both grid-connected and island mode of operation. Fault currents are then analyzed to determine the operation of conventional overcurrent protection schemes and their inability to detect and isolate the faults. A layout for an adaptive protection scheme using communication assisted protection devices is proposed to overcome the shortcomings of overcurrent protection scheme.