ABSTRACT: Presently most of the world’s energy supply comes from fossil and nuclear sources. In spite of the increasing issues of resource limitations and environmental pollution, these sources continue to be important in providing energy for the next few generations. However, these sources are expected to be less available and are of environmental concern. To meet the increasing global demand for energy and to allow for the decrease of environmental pollution, the uses of alternative or clean energy sources, which do not depends on fossil fuels and has a tolerable environmental impact, is increasing. Alternative energy sources (AES) like microturbines, photovoltaic (PV), fuel cells, wave energy and wind turbines seem to meet the requirement for clean energy. Such resources have not yet become a major part of the electrical power system grid. Integrating these generating sources into the existing power system grid, known as distributed energy resources (DER), can provide a more reliable and better quality power to consumers. The electricity obtained from these energy sources is normally unregulated and is not in a suitable form to be directly connected to the power system grids or to non grid-connected loads.