Topologies for uninterruptible power supplies

The authors review the development of uninterruptible power supply (hereafter referred to as UPS) over the years from one with a SCR front end charger with isolation at line frequency to one with a sinusoidal current input charger with isolation at high frequency (HF). The authors discuss the developments in the single phase low-power (less than 1 kVA) UPS topologies. Each scheme is analyzed briefly and its principal merits and demerits are identified.<>