Four-Wire Unidirectional Three-Phase/Level/Switch (VIENNA) Rectifier

This paper presents a four-wire Vienna rectifier (VIENNA4) and proposes a control system capable of balancing the partial DC link voltages in both symmetrical and asymmetrical loads. The main application for this type of rectifier is a transformerless AC-DC-AC converter used in uninterruptible power supplies (UPS). The proposed control scheme is verified by simulations and the measurements from the prototype. The rectifier system was designed to operate at a nominal output power of 10 RW with a DC link voltage of 700 V. The digital implementation of the control system and the modulator are realised with Motorola MPC555 microcontroller