Multipulse Ac-dc Converters for Power Quality Improvement

The revolution in power electronics has opened an era for widespread use of power converters of different power rating from few Watts to Mega-Watts. AC-DC converters are most widely used power converters as the distributed electric power is AC supply, while the applications based on DC supply as well as variable frequency AC supply, need conversion of AC supply into DC supply. Large current harmonics and poor power factor in the utility interface are common problems in AC-DC converters. These AC-DC converters are used invariably at the front end in numerous applications which may or may not be electrically isolated from the AC supply system depending on the rating and nature of the load and also the prevalent `Standards' requirements. The applications such as electrochemical, electrometallurgical and electrical heating processes, HVDC systems, adjustable speed drives, battery charging, aerospace and naval equipments, uninterruptible power supplies (UPS) etc., use AC-DC conversion at the front end. These processing industries and adjustable speed drives are main applications where large amount of power is involved in AC-DC converters. These AC-DC converters are generally diode based, thyristor based or self commutating device based converters depending on applications, size and cost. The simplicity in design and popularity of AC-DC converters have been considered as the reasons for them to be most neglected converters. The wide spread use of AC-DC converters for various applications has resulted in power pollution leading to failure of sensitive equipments, reduced efficiency, etc. This has led to development of power quality standards and hence attracted attention of many researchers for improving the power quality at AC mains. This research work aims at classifying and investigating different multipulse AC-DC converters that employ either diodes or thyristors.