Stability and Suppression Study for Low-Frequency Oscillations in Network-Train Systems

Electric multiple units (EMUs) have been the cause of low frequency oscillation (LFO) incidents in high-speed railway (HSR) network train systems (NTSs). In this paper a norm criterion with the advantages of simpler calculation while being less conservative than other norm criteria is introduced to analyze the stability of the NTS. A control strategy of EMU four-quadrant converters (4QCs) consisting of ac current passivity-based control (PBC) and dc voltage sliding mode variable structure (SMS) control, i.e. PBC-SMS, is proposed for LFO suppression. The NTS stability analysis with PBC-SMS results in superior critical LFO condition. A single EMU simulation validates the improved steady-state and dynamic performance of the PBC-SMS compared to other conventional methods; NTS simulations based on field tested network parameters verify the superior LFO suppression capability of the proposed method. Finally, guidelines for LFO suppression are recommended based on a comprehensive sensitivity analysis of the traction network, 4QC circuit and controller parameters of an NTS.