Three-phase 15kVA UPS system with power factor correction and high frequency transformer isolation

This work proposes a double conversion three-phase uninterruptible power system (UPS) with power factor correction, and high frequency (HF) transformer isolation. It's suitable for operation with line-to-line input voltages equal to 220 V or 380 V. For both input voltages, the proposed converter has almost the same efficiency processing the same output power. The front-end converter is based on three single-phase chopper modules, and the DC/AC converter is composed by a three-phase inverter with an additional leg to mitigate the voltage unbalance inherent to the series connection of DC-link bus capacitors. 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 (IC), and the use of few batteries in series due to the step-up stage. Principle of operation of the proposed system, implemented control strategy and experimental results obtained for a 15 kVA prototype are presented.