Very high efficiency UPS systems

Uninterruptible power supplies (UPS) are widely used to provide quality and reliable power for critical loads. In recent years, rising energy cost and environmental concern has been leading to significant improvements in the structure of the UPS systems. Until recently, UPSs with isolation transformer have been employed in on-line UPS systems, but today higher efficiency modern transformerless UPSs are common as a consequence of energy efficiency incentives and motivations. To reach higher efficiency levels the two-level (2L) inverter based structure has been replaced with the three-level (3L) inverter structure. In this paper, the 3L inverter structure based UPS is examined and its experimental performance is reported. Also, the change in size of 3L UPS is compared with the old systems and environmental effects are discussed.