The deregulation and liberalization of electricity market besides the increasing interest of'carbon
emissions and eliminating unnecessary transmission and distribution costs encourage the utilization of
Distributed Generation "DG. Therefore, DG is expected to penetrate within electrical power systems in
the near future in the form of small generating sources located clo~e to load centres. This paper
discusses the dynamic performance of some promising Distributed Generating (DG) units. The selected
units in this study are the wind turbine, the fuel cell, the micro turbine and the hybrid fuel cell-micro
turbine unit. The objective is to compare.among the dynamic pirformances of such units to evaluate
their behaviour under different operating conditions. Detailed models fdr the selected units including the
thermal description of the fuel cell are presented. The investigation study concentrates on the operation
of the DG units with an isolated load. Extensive simulation results are introduced to enable the
comparison among different units.