Impact of Source Voltage Unbalance on AC-DC Rectifier Performance

This paper presents a comprehensive study about the impact of source voltage unbalance on the performance of a three-phase ac-dc rectifier along with the harmonics injected by the rectifier load. The variation of different characteristic and non-characteristic harmonics with the degree of unbalance is investigated. The study also includes the effect of source voltage unbalance on harmonic distortion of different input and output characteristics of the rectifier. Since, the voltage sequence components play an important role in describing a more clear view of degree of voltage unbalance, an attempt has been made to identify the impact of sequence voltage components on total harmonic distortion and individual harmonic components in different phases. A full understanding of sensitivity of the current harmonic components to different unbalance voltage operating conditions is also obtained. To describe the unbalance in total harmonic distortion of current (THD_I) in three different phases, a new term "phase total harmonic distortion unbalance factor" (PTHDUF) is introduced. It was found that PTHDUF is proportional to the degree of unbalance/voltage unbalance factor (VUF).