Proposal of Three-Phase High-Frequency Transformer Isolation UPS Topologies for Distributed Generation Applications

A family of double-conversion three-phase uninterruptible power systems with power factor correction and high-frequency transformer (HFT) isolation topologies are presented in this paper. This might be a suitable alternative compared to large conventional uninterruptible power systems (UPSs) that are based upon bulky transformers that operate at the grid frequency. This system is commonly used to supply critical loads, but nowadays, due to the increasing interest in renewable energy integration and distributed generation (DG), it can also be a suitable solution for energy storage in microgrids or renewable-power-conditioning interface applications. The three-phase HFT UPS used for further analysis is composed of single-phase chopper modules, one three-phase boost module, and one three-phase inverter. The relevant features are soft commutation of the controlled switches in the chopper stage, simple control strategy that can be implemented with well-known integrated circuits, and the use of a few batteries in series due to the same reference of the step-up stages. The principle of operation of the chosen system for experimental validation, the implemented control strategy, and the experimental results obtained for a 15-kVA prototype are presented.