Development of a single-phase half-bridgeactive power filterwith the function of uninterruptible power supplies

Analysis and implementation of a single-phase half-bridge active power filter with the function of uninterruptible power supplies is presented. The system provides the combined functions of battery bank energy storage, power-factor compensation, harmonics elimination and uninterruption of the power supply. When the utility is in normal operation, the proposed system will not only supply DC power for battery charging, but also function as an active power filter for improving the power factor and reducing the current harmonics on the utility side. If the utility power fails, the proposed system will function as an inverter immediately, to supply the battery power to the AC load. Analysis for the proposed system is given first, and a personal computer is then used to implement digitised control of the proposed system to facilitate experimental evaluations for a 1 kVA prototype. The feasibility and multi-functional results obtained indicate that the proposed system can be realised by using a digital signal processor as the core controller for cost reduction and reliability enhancement.