The Impact of Source Unbalance on Harmonics from an AC to DC Rectifier

Power quality is a very important aspect of power systems, and it directly affects the efficiency of power equipment. Part of improving the power quality is reducing current and voltage harmonics in the system, and knowing what harmonics to expect makes that job easier. The harmonics produced by an AC-DC rectifier with a balanced three-phase source are well known, but the total effects an unbalanced source may have on harmonics are not known. This study attempts to find the impact that source unbalance may have on the harmonics produced by a rectifier by performing a series of simulations. These simulations consist of a balanced source and seven different unbalanced sources simulated on a three-phase bridge rectifier with three different RC loads and two different RL loads. The results of these simulations showed that source unbalance produced triplen harmonics, had a greater impact on higher order harmonics, and had a different effect on each load.