Analysis and Adaptive Mitigation Scheme of Low-Frequency Oscillations in AC Railway Traction Power Systems

The diffusion of modern electric trains equipped with high-power voltage-source converters has introduced new dynamic interactions with the ac traction power system that may create unexpected low-frequency oscillations (LFOs). This paper presents for the first time a detailed analysis of the operating conditions of electric trains and a traction network, revealing that specific changes in the operating conditions of the train-network system are responsible for the oscillations and may lead to instability. The study is carried out with an analytical dynamic model considering the transient direct current control and focuses on evaluating how the mismatch between the parameters of the controller and the controlled object of the train-network system affects the system dynamics and stability. It is shown that the retuning of controller parameters improves the dynamic performance and the stability of the train-network system, and hence an adaptive mitigation method is proposed to mitigate LFOs adopting a new design of the controller with minimal change and cost to the original system, which provides a simple solution to guide engineering practice in railway traffic. Simulations and experimental results are presented to fully validate the proposed method.