Comparison of three-phase PWM rectifiers to interface Ac grids and bipolar Dc active distribution networks

Dc active distribution networks seem to be a technically viable solution where high transmission efficiency, power quality, reliability and distributed generation are required. Modern power conversion devices are to be employed in order to create such networks by connecting them to three-phase ac power systems. This work present the evaluation of two-level and three-level (NPC) bidirectional voltage source rectifier topologies for bipolar dc active networks from the perspective of power semiconductor efforts, efficiency, volume and weight. The evaluation methodology based on the rotating reference frame is used in the analysis of a 160 kVA NPC converter feeding unbalanced dc loads and the impact of this in the converter volume and weight is presented. Furthermore, the maximum dc-side load unbalance for the NPC rectifier is derived.