An on-line UPS system that eliminates the inrush current phenomenon while feeding multiple load transformers

Numerous industrial facilities involve the installation of load transformers with their respective loads. As loads are turned on and off, these transformers are energized and de-energized, respectively, which can cause serious disturbances to sensitive loads. An inrush current, which typically occurs when a transformer is energized, can easily be observed using on-line uninterruptible power supply (UPS) systems feeding such loads. This paper proposes an on-line UPS system that eliminates the inrush current phenomenon caused by the energizing of load transformers. The UPS inverter specifically utilizes a fast acting current control scheme that enables it to regulate current for the load during all energizing conditions of load transformer connected to the UPS system.