UPS Outage-Mode Output Power Capacity Expansion Approach via Bi-directional Converter

An outage-mode output power capacity expansion approach of uninterruptible power supplies (UPS´s) with full utilization of the existing components is proposed in this paper. The proposed UPS system consists of a bi-directional AC/DC converter and a voltage controlled inverter (VCI). When the utility is normal, the bi-directional converter acts a power factor correction (PFC) rectifier to let the line current with low harmonics and near unity power factor. On the other hand, when the utility fails the bi-directional AC/DC converter can also function as a current controlled inverter (CCI) and is connected in parallel to the VCI. With such instantaneous current sharing controller technique, the load current is equally shared by each inverter with fast response. When compared with conventional UPS´s, the proposed built-in parallel technique possesses the advantages of low implementation cost, high power density, fast response, and precise current regulation. Finally, simulation results with different operation modes have demonstrated the feasibility of the proposed UPS system.