Energy Storage Unit for Uninterruptible Power Supply

Generally uninterruptible power supply (UPS) is used to maintain a stable electric power supply to critical loads with high quality power protecting them against unexpected power failure. For example, medical facilities and data-storage computer systems require fast response, compensation and immediate availability of electrical power. Considerably affect these characteristics is energy storage units like a battery bank. Energy storage units in UPS system should supply power to the load when the ac line fails. If they are not capable to implement this important role, then the whole UPS system fails even though it employs well-designed power electronics circuits. To satisfy the requirements, we propose a common-arm based UPS equipped with a dc-to-dc converter employing an energy storage unit. The proposed UPS consists of ac-to-dc and dc-to-ac converter sharing a common-arm, a static switch for bypassing, and the proposed dc-to-dc converter. The ac-to-dc converter is used for maintaining the input current sinusoidal and in phase with the input ac voltage to obtain high power factor. It also supplies the desired dc-link voltage suitable for proper operation of back-end inverter. The dc-link is a part of the proposed dc-todc converter. It has a series connection of a battery bank and a capacitor. The dc-to-ac inverter needs to synthesize high quality output voltage wave. Operational mode is analyzed and the validity of the proposed UPS with the energy storage unit is verified by experimental results.