A mixed AC/DC model for railway power systems

Abstract

A method to study railway power supply systems with AC power distribution networks and DC power feeding is presented in this paper. The aim of this work is to obtain a DC model of the whole system in which AC networks are converted into equivalent DC ones. Relationships between AC and DC quantities on both sides are set using the equations of multiple bridge rectifiers as described in the literature. Particular DC models for transformers and 3-phase lines are used to represent the corresponding voltage drops. Specific base quantities are used for AC and DC parts of the circuit in order to obtain a simplified circuit. This model is used to solve a DC load flow problem. Real values of voltages, intensities and power flows can be obtained by using the proper base quantities. Additionally a correction has to be made to improve the power flow results calculated previously, due to pure resistive representation of transformers and AC lines, so a fine approximation is achieved.