Small-signal input impedance modeling of line-frequency rectifiers

This paper presents a systematic method for modeling small-signal input impedance of line-frequency AC-DC converters. The objective is to develop proper models that can be used for stability analysis of AC power systems with significant DC loads powered by such converters. The proposed modeling method uses harmonic linearization and Fourier analysis techniques to describe the current and voltage mapping process through the converter switching circuit. The voltage and current mapping relations are then combined to give an impedance mapping model which converts the impedance of any circuit or system connected to the DC output of converter into a corresponding small-signal input impedance of the converter at the AC side. Similar relations can be used to map the AC source impedance into the DC side to give the equivalent dc source impedance for stability analysis of the DC subsystem. This paper focuses on the basic principle of the impedance mapping method and uses a single-phase diode rectifier circuit to demonstrate the modeling process. The resulting ac input impedance model is validated by detailed circuit simulation as well as experimental measurements.