Low-Frequency Oscillation Analysis in Train-Traction Power Supply System Using an SISO Voltage Loop Model

Abstract

Low-frequency oscillation (LFO) in the train-grid coupling system severely endangers the stability and safety of railway operation. It is well known that this phenomenon is caused by impedance mismatch among the trains and the traction power supply system (TPSS). A novel voltage loop model of the single-phase pulsewidth modulation rectifier is proposed in this article. Unlike the commonly adopted multi-input multi-output (MIMO) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> impedance model in the literature, this is a single-input single-output (SISO) model that enjoys some advantages, such as easier calculation of the system poles and quantitative analysis of the stability margin. The most attractive character of this model in comparison to the MIMO one is perhaps the decoupling of the controller and the voltage loop. This paves the way toward the analytical design of the dc-link voltage controller (DVC), whereas the impedance model is mainly useful for analysis. Furthermore, the maximum amount of trains allowed for keeping stability is derived from the steady-state equation. Robust stability margin (RSM) and sensitivity analysis are adopted to quantitatively investigate the influence of the control parameters and the circuit element parameters. LFO is guaranteed to be eliminated permanently by adjusting the controller parameters.