Quantitative Assessment Mechanism of Low Frequency Oscillations in Train-Network Systems

Low frequency oscillations (LFOs) in the electrified train-network system can lead to serious traction blockade accidents. Although impedance models and stability analysis tools have been applied in existing studies to address specific cases, a generalized mechanism to address LFO is still not established so far. This paper proposes a quantitative assessment method to reveal the underlying mechanism of LFOs. Founded on the improved Nyquist criterion, a stability margin indicator is defined to concretely describe system stability, then its corresponding expression is derived by combining the simplified impedance model as the basis for quantitative analysis. To this end, the identified negative resistances in the impedance model are revealed as the root cause of LFOs. Besides, theoretical justification for the impact of parameter tuning on the system stability is provided based on the explicit formula of the stability margin indicator. Finally, the effectiveness and accuracy of the theoretical analysis are verified under simulations and hardware-in-the-loop experimental conditions.