Three-phase AC-DC-AC converter with shared legs and floating H-bridges

Abstract

This work proposes a three-phase AC-DC-AC converter suitable for operation as unified power quality conditioner (UPQC). The proposed converter is composed of a six-leg three-phase cell connected with H-bridge floating cells at the grid side. This configuration makes three-legs of the six-leg cell shared between load and grid. The six-leg cell is naturally able to cope with all load unbalance, such that no current unbalance is transmitted from load to grid. Additionally, the H-bridges provide multilevel features to the converter grid side, reducing harmonic distortion. Two operations of the proposed converter are analysed: DC-link voltage ratio of 3:1 and 2:1. Converter model, space vector pulse width modulation (SVPWM) and control strategy are presented. The proposed converter is compared with conventional solutions considering harmonic distortion, semiconductor losses, average switching frequency, number and reverse blocking voltage of semiconductor devices. Experimental results are presented for validation.