Transformerless three-phase on-line UPS with high performance

A transformerless three-phase on-line uninterruptible power supply (UPS) is proposed. The proposed UPS is composed of a rectifier, an inverter and a battery charger/discharger. The rectifier regulates a DC-link voltage and performs power factor correction. On the other hand, the inverter provides a regulated sinusoidal output voltage and has the current-limiting capability for an impulsive load. The battery charger/discharger reduces the number of battery and supplies the power demanded by the load in the event of the input power failure or abrupt decrease of the input voltage. Since both neutral lines of the input and output voltages are connected at the centre of the DC-link, the need for an isolation transformer is eliminated and the size, weight and cost of the system are significantly reduced. Additionally, new control algorithms of the rectifier, the charger/discharger and the inverter are proposed.