Renewable uninterruptible power supply system deploying a single-phase front-end converter with integrated PFC and DC-DC functions

This paper presents the development of a single-phase online Uninterruptable Power Supply (UPS) system using a HPF front-end Boost converter with integrated Power Factor Correction (PFC) and DC-DC functions and an ordinary Full-Bridge as the single-phase output inverter. Besides the front-end stage with integrated PFC and DC-DC functions, the main feature of the proposed solution is the use a Proton Exchange Membrane Fuel Cell (PEMFC) as an energy storage system in substitution to batteries banks, eliminating the obvious drawbacks related to lifetime and maintenance issues. Supercapacitors are deployed in order to provide a proper startup of the PEMFC and to improve its dynamic response as well. Both, the front-end stage and the output inverter stage, are fully controlled using a single Digital Signal Processor (DSP). The control strategy is based on the average current control method for sinusoidal input current imposition and the standard phase-shift open loop control for the output inverter. During fault conditions or even in conditions of severe voltage sags in the ac network, the PEMFC is activated assuring the continuous energy supply to the output inverter connected to the DC-link and to the AC load as well. In this paper the authors present some theoretical concerns and the main simulation and experimental results obtained.