Unified Power Quality Conditioners

In this chapter, the authors present analysis, control, and steady-state operation of unified power quality conditioners along with series– parallel uninterruptible power supply (UPS) systems. They explain the topology, current and voltage control, and performance of these systems in different operating modes. The main purpose of UPS systems is to provide critical loads with uninterrupted, reliable, and high-quality power. UPS systems, in fact, protect critical loads against power outages as well as over- and under-voltage conditions. UPS applications include medical facilities, life-support systems, data storage and computer systems, emergency equipment, telecommunications, industrial processing, and on-line management systems. The line-interactive UPS system has better efficiency, but cannot provide tightly regulated output voltage and high input power factor at the same time. Having eliminated the main drawback of doubleconversion UPS systems, the series–parallel UPS topology appears to be a strong competitor of on-line UPS systems in many applications.