Input Impedance Modeling of Multipulse Rectifiers by Harmonic Linearization

Multipulse rectifiers are used in large industrial drives, aircraft, electric ships, and other systems, where limits on harmonic currents prohibit the use of conventional three-phase, six-pulse rectifiers. The large power rating of these rectifiers and the dynamic nature of the loads often necessitate the study of their dynamic interactions with the source, which can lead to system stability and power quality problems if not properly designed. This paper presents input impedance models for multipulse rectifiers that can be used for such system stability and dynamic power quality analysis. The modeling method is based on the concept of harmonic linearization and makes use of analytical mapping functions that describe voltage and current transfer through multiphase diode rectifiers. Input impedance models are developed first for general N-phase rectifiers, and then combined with a model of the phase-shifting transformer to define the three-phase input impedance. Magnetizing inductance and line commutation due to transformer leakage inductance are also considered. Details of the modeling method are presented using an 18-pulse rectifier as example, and experimental measurement results are also presented to validate the models.