Impacts Of Intermittent Renewable Distributed Generation Technologies On Distribution System Performances

In the last few years, deregulation of electric power sector, the economic and environmental concerns over electrical energy derived from fossil and nuclear fuels, the advancement in technology, and the growing requirements for high reliability have created renewed interest in smaller distributed generators operating in parallel with the electric distribution networks.There are several benefits associated with the use of Distributed Generation (DG), such as the system power losses reduction, transmission and distribution upgrades deferral, improved supply reliability and green house effects reduction. However, the interactions between DG and the distribution system in which it is embedded involve several phenomena that are worth careful investigations. If not properly handled, the integration of DG can result in lower reliability and even in a reduction in power quality. Hence it is necessary to develop analytical tools and to conduct thorough analyses and careful studies of the interactions between DG technologies and the distribution system.This thesis is concerned with the interactions between DG and the electric power distribution system and the impacts that the first can have on the second one's performance. The analysis is focused on determining the impacts of Intermittent DGs (IDGs) on distribution network performances i.e. power quality and reliability, power losses, voltage profile, short circuit current levels, protection coordination and the impact of power system events on the operation of IDGs. The thesis first presents the operational and planning impacts of IDGs on the power system. Secondly, model and simulation algorithm of Wind/PV hybrid generation system suitable for reliability impact study are developed. Case studies were carried out to validate the model and to examine the effect that Wind/PV hybrid IDGs had on system reliability. Thirdly, steady state models that support voltage profile and power losses impacts assessment of fixed speed wind turbine systems are presented and validated. Fourthly, model and dead-beat control structures suitable for grid fault response simulations of the fixed speed and variable speed wind turbine systems, and for ride-through capability analysis of variable speed wind turbine units are suggested. Since the induction machine is currently the most widely used electrical generator in wind turbine applications, a big effort has been paid in dynamic and steady state modelling of Wind Energy Conversion Systems (WECSs) based on it. The basic control structure for these generation units in grid-connected mode is treated. A controller design method based on predictive dead-beat control strategy is presented. The target was to develop a control structure for the active and reactive power that achieves fault ride-through capability of Variable Speed Asynchronous Machine (VSAM) WECSs. The response of a VSAM-WECS to grid disturbances is simulated. A 30% voltage dip (70%remaining voltage) is handled very well.From the results of case studies and contribution, this work provides another reference for system planners and operators in choosing the alternative supply source to achieve a desired reliability level for their systems, and in choosing a suitable evaluation methodology when dealing with intermittent distributed generations.