Development of Adaptive Overcurrent Relaying Scheme for IIDG Microgrids

Current power system interest is intensely going towards the renewable energy integration to the system in the form of microgrids. Since microgrid has two major operating modes as stand-alone and grid-connected, cause a major issue in protection during the transition of the two operating modes. When the operating mode changes from the grid-connected mode to stand-alone mode, fault current magnitude is reduced drastically. The conventional overcurrent protection experience several issues including selectivity and sensitivity during this transition. Also the fact that rotating machines providing more fault current than that of a power electronic based equipment is another issue in modern microgrids. As a solution for these problems adaptive protection can be used to adapt to the two situations and change its settings according to the fault current magnitudes. This paper demonstrates an adaptive protection structure for Inverter Interfaced Distributed Generator (IIDG) microgrids. This structure is developed with a central control system that can detect the operation mode of microgrid. MATLAB Simulink is used to simulate the relay structure and the test system. The hardware implementation is currently being developed and not considered in this paper. The result shows that the relay structure adapts to the situation by sensing the operation mode efficiently.