Micro grids constitute the ultimate form of decentralized electricity, heat and cold supply whose operations separated from the main distribution system i.e. autonomous or connected to the distribution system i.e. grid-connected. Grid-connected micro grid can be of help during a system fault, by supplying power to the main distribution system, feeding part of its loads for fault detection and service restoration. Micro grids have emerged as a competitive alternative to the final delivery of energy to consumers in combination with on-site production of heat. Distributed generation grouped in micro grids can introduce a richer set of tools for supply of o heat and power, at higher reliability, security, flexibility and power quality in the conventional grid. A micro grid is typically managed through a central controller that monitors the system parameters, coordinates energy resources, balances loads and controls electrical loads, and disconnects and reconnects of the micro grid to the primary grid. Micro grids with no central controller are not common but are technically feasible, with distributed energy resource having an individual controller and the individual controllers operate in a coordinated manner.  Micro grids can be an effective option to increase the energy resilience, by providing a functional electric power system capable of operating independently of the main grid. The main grid usually supplies primary power, while the micro grid provides secondary dispatchable power in the event of a grid failure. Emergency diesel generators can provide power directly to loads in the event failure of the primary grid and the micro grid. Proper design and planning of microgrids is important for them to yield all the advantages of the distributed energy concept for the power systems, both local and the clinked central power system. This calls for a reliability -oriented design for microgrids that utilise a large share of the variable and intermittent renewable energy-based, and power electronics-interfaced distributed energy resources. Experience has shown that the power electronics used are prone to wear-out failure and can potentially have adverse effects on the on the performance of the entire power electrics dominated power system. The many benefits associated with application of microgrids have contributed to their significant growth and penetration in decentralized power generation globally. However, challenges are still encountered with respect to design, operation and control for both island and on grid mode of operation