In recent years, with the increase of nonlinear loads drawing nonsinusoidal currents, power quality distortion has become a serious problem in electrical power systems. Active filters have been known as an effective tool for harmonic mitigation as well as reactive power compensation, load balancing, voltage regulation, and voltage flicker compensation. On the other hand, uninterruptible power supply (UPS) systems provide uninterrupted, reliable, and high-quality power for vital loads.
They, in fact, protect sensitive loads against power outages as well as overvoltage and undervoltage conditions. UPS systems also suppress line transients and harmonic disturbances. Applications of UPS systems include medical facilities, lifesupporting systems, data storage and computer systems, emergency equipment, telecommunications, industrial processing, and on-line management systems. Generally, an ideal UPS should be able to deliver uninterrupted power and, simultaneously, provide the necessary power conditioning for the particular power application.
This book describes harmonic-producing loads, effects of harmonics, and harmonic mitigation methods using active filters. Different topologies of active filters and UPS systems, their applications, configurations, control methods, modeling and analysis, and stability issues are also comprehensively discussed. Recent advancements in the area of power electronics have resulted in a great variety of new topologies and control strategies for active filters and UPS systems. The research has been focused mainly on improving the performance and expanding application areas of these systems.
The issue of cost reduction has been attracting the attention of researchers. Reducing the number of switches allows one of the most significant cost reductions. A different technique is replacing controlled switches such as IGBTs, MOSFETs, and thyristors with diodes. Another approach for reducing cost is to develop topologies that employ switches with lower reverse voltage stresses and lower current ratings. This book addresses these new trends in detail.
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