The concept of power quality is a major concern in modern power systems. The growth of sensitive loads and their susceptibility to various disturbances are the main reasons of these concerns. Voltage sag, swell and outage are three important and popular events that cause the majority of power quality related problems. Different solutions have been proposed for relieving such problems such as using Constant Voltage Transformers, UPS, motor-generator sets and transfer load between two existing feeders. The latter, which is particularly suitable and economical for large loads and facilities, may be performed either by mechanical or by static switches. The nature of most modern loads does not allow the large delay associated with transfer of power by mechanical switches. Consequently, the issue of static transfer switches has recently attracted the attention of both industries and researchers. It is possible to significantly reduce the transfer time between two feeders by using static switches. However, the possibility of short circuiting the feeders on one hand and the variety of disturbances and existing loads on the other hand result in some complications in this process. This thesis is concerned with finding a suitable algorithm for static transfer switches with adequate performance under all operating conditions. Specifically, the operation with light loads, regenerative loads and when the supplies are slightly out of phase are considered. Extensive simulation results show the validity of analysis.
