Analysis of Low-Frequency Oscillation in Electric Railways Based on Small-Signal Modeling of Vehicle-Grid System in dq Frame

The line-side converter, which can represent an ac-dc-ac drive electric vehicle when analyzing the low-frequency oscillation in electric railways, is modeled in dq frame with the proposed single-phase dq-decomposition method. With this model, an underdamped mechanism of the vehicle-grid interaction is confirmed. Besides, a low-frequency stability prediction approach is presented, based on the dominant-pole analysis and verified by the simulation and the testing result. The proposed modeling method and prediction approach benefit in three aspects: It is more convenient to rebuild the model with a change of either the line-side converter controller or the system condition, much quicker to predict the low-frequency instability and more explicit to guide the modification of the controller software to damp the low-frequency oscillations.