Transformerless UPS System Based on the Half-Bridge Hybrid Switched-Capacitor Operating as AC-DC and DC-DC Converter

A single-phase transformerless online uninterruptible power supply (UPS) is proposed in this article. This UPS is based on the new half-bridge doubler-boost with switched-capacitor operation. It is capable of operating with ac and dc input sources. The proposed converter provides a high power factor and improves power efficiency for line voltage applications. The switched capacitor concept allows a natural balance of the dc bus capacitor voltages, both in the ac-dc mode and the dc-dc mode. It presents a common point between the line voltage source, load, and batteries. This characteristic makes it possible to eliminate the common mode current, reducing problems with electromagnetic interferences and allowing the use of a simple bypass system. The feasibility of the proposed UPS is verified by experimental results from a 2.5-kW prototype with an efficiency of up to 94.9% and unity power factor.