Floating on the DC bus is a battery bank that provides energy storage to keep the system operating during an interruption. The DC voltage is then inverted back to single- or three-phase 60 Hz AC to operate the load. The core value of an Uninterruptible Power Supply (UPS) is “Energy storage during normal operation + Voltage regulation, seamless switching to battery power when the mains supply fails”. A UPS system is an autonomous source of alternate power that is used to supply sensitive electronic loads such as computer centers, telephone exchanges and many industrial-process control and monitoring systems. The most common types are offline and online UPS systems. In this article, you will learn the working principle of UPS with block diagrams.