Assessing High-Order Harmonic Resonance in Locomotive-Network Based on the Impedance Method

Many new types of locomotives are put to use in electric railway systems, resulting in instability problems such as high-order harmonic resonance occurring as a consequence of the interaction between the electrical locomotive (including electrical multiple units) and the traction network. In order to investigate this problem, this paper adopts the impedance-based approach to analyze the stability properties of the system interaction. The detailed impedance of the traction network is obtained by taking its distributed parameters into account. Then the locomotive converter with single-phase transient current control algorithm (TCCA), which can represent the locomotive when performing the impedance-based stability analysis, is modeled as the dq-frame impedance by single-phase dq decomposition. By plotting bode diagrams of the impedance for the traction network and the locomotive separately, and calculating the phase margin at the intersection point of the magnitude of the two impedances, the stability of the locomotive-network system is evaluated and thus the high-order harmonic resonance can be predicted. Moreover, a time-domain model of locomotive-network systems is established in this paper, which can reproduce the high-order harmonic resonance in the time domain as a first validation step of the analysis. Finally, a field test in a traction substation of the Beijing-Harbin Railway is carried out to finally validate the effectiveness of the proposed method. The stability analysis method in this paper is simple and effective without the need for a complex calculation of some norms or Eigenvalues. As a result, the high-order harmonic resonance can be predicted before a new type of locomotive is put into use.