الفهرس 
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Abstract
The penetration of renewable energy systems as a type of distributed generation has been significantly expanded worldwide. Therefore, Microgrids have been considered as one of the suitable and efficient alternatives for this integration of distributed generation units in the utility grid. A Microgrid can be defined as a group of interconnected distribut-ed energy resources (DERs) and energy storage systems (ESS) that are controlled to supply power to the loads for which it is designed. It can be connected and disconnected from the grid. Also, a microgrid can be defined as a smaller version of the traditional power grid.
DC microgrid has attracted a great interest nowadays, as it offers several ad-vantages like simple integration of DC DERs such as photovoltaic and fuel cells, efficient supply of DC loads and reduction of conversion stages.
This thesis presents the modelling, operation and control of low voltage (LV) DC microgrid, where the system is operated in both grid connected and islanded modes. Addi-tionally, PV system intermittency has been taken into consideration in the simulated cases. Also, the change in power demand has been studied. Control strategy is performed through DC bus voltage monitoring. Both Bidirectional converter of ESS, and voltage source converter (VSC) interfacing the utility grid are controlled to achieve the required voltage stability and power balance. Simulation results have shown that integration of DC microgrid with batteries achieves more flexibility and reliability in the system through balancing power demand and generation by the aid of different controllers. Then the challenges facing the protection of DC microgrids, in addition to fault detection methods and fault interruption techniques are introduced.
Finally, a protection scheme is proposed that can be able to interrupt the fault as fast as possible. This occurs by using Semiconductor based circuit breakers also known as solid-state circuit breakers (SSCB). Consequently, insulated gate bipolar transistors (IGBT) are used as power switches. In order to satisfy the requirement of fast operation and high short circuit current withstanding capability.
The objective of this work is to develop a protection strategy that can detect and isolate the fault quickly and without shutting down the whole system. Fault current of the faulted section is extinguished through freewheeling path, so it reduces system damage. Furthermore, the protection strategy is done through main and backup protection to en-hance system reliability and ensure that the fault is interrupted. The proposed protection system is simulated and verified through MATLAB/Simulink.