Stability Analysis of PV Plant-Tied MVdc Railway Electrification System

As ac electric railways have various problems (e.g., power quality issues, complex catenary networks, limited supply region, and passing neutral section), the medium-voltage direct current (MVdc) railway electrification system (RES) may be a potential alternative electric railway mode and can be freely accessed to the renewable energy systems. However, some instability issues may be aroused due to the interaction between flexible MVdc RES and electronic-based dc-dc equipment. In this paper, a comprehensive small-signal impedance model, combining a photovoltaic (PV) plant and an MVdc RES, is performed, while available electric variables and control parameters are taken into consideration. Then, a novel passivity-based stability criterion (PBSC) is introduced to determine the instability issue about associate influential factors, including proportional and integral parameters of traction substation and PV converters, the power of train converters, and the dc catenary length. A virtual impedance control scheme is designed to stabilize the system. The experimental results demonstrate that the PBSC can identify the instability in the MVdc RES. The results also match well and support the conclusions obtained.