Mitigation of voltage sag and swell using direct converters

Abstract

The power quality gets degraded due to the disturbances, occurring in the transmission as well as in the distribution sides Flexible AC Transmission System devices are employed at the transmission side to overcome the power quality problems The Custom Power System CUPS devices employed in the distribution side compensate for sags swells harmonic distortions interruptions etc to improve the power quality newlineThough many CUPS devices are commercially available in the market dynamic voltage restorers DVR are developed recently to improve the power quality Generally the DVR topologies are categorized into three main groups Under first group the required energy for compensation is taken from the energy storage element The second group of the topologies uses ac dc ac conversion In these topologies the required dc voltage is provided through a transformer from the grid source side or load side via a rectifier In both the groups of topologies it is necessary to embed a large capacitor in the dc link in order to maintain the voltage across the converter DVRs based on energy storage units suffer from limitations such as need of large and costly energy storage units maintenance problems associated with the storage units and higher weight per kVA rating The third group of the topologies employs direct ac ac conversion without energy storage devices So far limited analysis has been done on the DVRs without energy storage devices newline newline