Impedance-Based Harmonic Instability Assessment in a Multiple Electric Trains and Traction Network Interaction System

This paper presents an impedance-based method to systematically investigate the interaction between multi-train and traction networks, focusing on evaluating the harmonic instability problems. Firstly, the interaction mechanism of multi-train and the traction network is represented as a feedback interconnection of the two subsystems, i.e., an equivalent output impedance of the traction network and an equivalent input admittance of the multi-train. Then the harmonic instability is evaluated through a series of pole-zero diagrams drawn from the closed loop transfer matrix of the multi-train and traction network interaction system. The interaction system is unstable and the harmonic instability will happen if there are some high frequency poles of the closed loop system located in the right half plane. This method is used for analyzing the harmonic instability phenomena and its characteristics, its factors and also possible mitigation schemes. The theoretical results are further validated by the simulations and experiments.