Dynamic modeling of short-circuit behavior of a six-pulse rectifier

Abstract

Existing models describing the dynamic behavior of a six-pulse rectifier during a short-circuit fault condition are derived from switch models using average value parametric functions. Unlike these models, new non-parametric dynamic models have been developed using analytical average-value modeling approach. In this modeling approach, depending upon the number of switches conducting during a switching cycle, the operating point of the rectifier is brought into one of three modes of operation of a six-pulse rectifier. The model for each mode is represented by a differential equation and the operating model is selected based on firing angle and overlap angle functions derived in this paper. They completely characterize the dynamic behavior of current flowing through the DC inductor for a wide range of operating conditions with the exception of harmonics and asymmetrical currents which are dominant for faults occuring at the terminals of the rectifier upstream of the smoothing inductor. I. INTRODUCTIONPhase controlled rectifiers are used in a number of applications like HVDC transmission, brushless synchronous machine excitation, variable speed electric drives, DC traction power systems and it is also considered for shipboard power systems. A dynamic model of the rectifier is useful for design and assessment of protection and stability of the power supply systems.A six-pulse rectifier supplied by a a thevenin equivalent AC source has been considered for analysis in this paper. The short-circuit AC impedance can be used to model rectifier transformer leakage reactance and the AC source emf can be considered as infinite bus AC voltage source. Steady-state and transient analysis for the above mentioned model has been performed in many literatures.In [1], a steady-state model of the rectifier has been analyzed with an explanation of modes of operation of the rectifier for various DC load currents. In another model presented by Denning an envelope of AC short-circuit current waveform of the rectifier is used for estimating DC short-circuit current close to the rectifier. This model was further analyzed by Pozzobon in [2]. According to [3], a model proposed by Fujimura and Honda estimates high impedance DC fault current and initial rate of rise by using an equivalent DC circuit model consisting of a DC voltage source and a series resistor and an inductor calculated with three-diode conduction pattern.Analytical and parametric average value models (AVM) of six-pulse rectifier have been presented in [4], and [5]. These AVMs are capable of determining the dynamics of

Interrupting Short-Circuit Direct Current Using an AC Circuit Breaker in Series with a Reactor

“…An average value model is developed in [27,28] for mode 1. Novel average value models for modes 2 and 3 are developed in [31]. Due to the assumptions taken in the AVM approach, these models are applicable only for rectifiers with high filter inductance Tables 3, 4, and 5, respectively.…”

“…These six switching intervals are identical in terms of the number of conducting switches in the upper and lower half of the bridge and each interval lasts 60•. Depending upon the number of diodes that conduct simultaneously during a switching interval, the rectifier would operate in mode 1, mode 2, or mode 3[27][28][29][30][31].The different modes are explained with the help of…”