Mitigation of Current Harmonics for Multipulse Diode Front-End Rectifier Systems

Multipulse rectifier system has been shown to be a cost-effective harmonic solution in many industries where IEEE 519 is specified. However, it is susceptible to poor quality of the input source of the power distribution system where the phase unbalance of the source voltage and preexisting low-order harmonic voltages are presented. A small amount of voltage unbalance with preexisting harmonics can create large amount of current harmonics to the input source. Consequently, a stricter preexisting voltage total harmonic distortion condition has to be specified for an 18-pulse rectifier to meet the IEEE 519 current-harmonics requirement. This paper introduces a dc link passive filtering method to solve this problem. It greatly reduces the current harmonics created by the phase unbalance, the fifth-, and the seventh-order voltage harmonics by adding several series LC resonant loops into the dc link. As a result, the proposed 18-pulse rectifier can meet IEEE 519 under several abnormal source voltage conditions of the ac line. Theory analysis, simulation, and experimental result are provided in this paper to verify the effectiveness of this method