Power electronic devices are non-linear loads that create harmonic distortion and can be susceptible to voltage dips if not adequately protected. The most common economically damaging power quality problem encountered involves the use of variable-speed drives. THREE-PHASE ac-dc conversion of electric power is widely employed in adjustable-speeds drive (ASDs)), uninterruptible power supplies (UPSs), HVDC systems, and utility interfaces with non conventional energy sources such as solar photovoltaic systems (PVs), etc.Traditionally, ac-dc converters, which are also known as rectifiers, are developed using diodes and thyristors to provide uncontrolled and controlled unidirectional and bidirectional dc power. They have the problems of poor power quality. This book is an endeavour towards analyzing the different multi-pulse converters in solving the power quality problem in a three-phase converter system.

Isolated power systems are commonly found in rural and remote areas of the world. These systems represent the alternative to grid connection, where interconnection to a large grid is not viable due to high cost and/or geographical obstacles. Furthermore, power systems such as those onboard of ships, in oil exploration areas and remote mining districts are characterized by limited generating capacity, supplying loads which can consist of significant amount of motor drives and power converters. The use of series compensators (SCs) in improving voltage quality of isolated power systems is to be considered.A control strategy for the SC is to be developed to regulate power flow. This is achieved through phase adjustment of load terminal voltage.Through a phase adjustment technique, we can show that the voltage quality across the terminals of the protected load can be controlled.