Modeling and Harmonic Instability Analysis of the PET-Based Train-Grid System

The power electronic transformers (PET) show huge attractiveness in railway traction system due to their advantages, e.g., high efficiency and light weight. However, in the PET-based train-grid (PTG) system, the issue of harmonic instability remains, and few efforts have been made toward this problem. To address this, in this paper, the complete impedance model of the PTG system is first established in the dq-frame. Then, the frequency-sweep method is accordingly implemented to verify the accuracy of the model. With this, considering the interactive influence of train-grid impedance, the impedance-based stability criterion is applied to analyze the system stability. Especially, the cause and influence law of harmonic instability are explored in the PTG system. Finally, the hardware-in-the-loop (HIL) tests are conducted to verify the effectiveness of the discussions.