PROJECT 2

Title: Transformer-less Online Uninterruptible Power Supply (UPS) system

Abstract: Uninterruptible power supply (UPS) is widely used to supply power to critical load and provides protection against power failure and other anomalies of power line. A transformer less online uninterruptible power supply (UPS) has been proposed in this paper. The proposed system consists of totem-pole bridgeless boost rectifier, battery charger/discharger, and an inverter. The rectifier operates under zero voltage switching (ZVS), provides regulated DC link voltage with power factor correction. The novel battery charger/discharger ensures the transformer-less operation by reducing the battery bank to only 24V, and regulates the DC link voltage during battery power mode. The inverter provides regulated output voltage to the load. By introducing high gain battery charger/discharger, the battery bank is reduced considerable, which minimize the size, weight, and cost of the system. A new cascaded slide mode and proportional-integral control has been proposed. The controller regulates the output voltage for both linear and non-linear load, shows excellent performance during transients and step change in load. Operation principle and experimental results of 1kVA prototype has been presented to verify the validity of the proposed system.