Vehicle-Grid System Stability Analysis Based on Norm Criterion and Suppression of Low-Frequency Oscillation With MMC-STATCOM

In recent years, low-frequency oscillation (LFO) events sometimes occur between the traction network and the electric motive units (EMUs) in vehicle-grid systems of a highspeed railway when multiple EMUs access the traction network. Some measures have been taken from the vehicle side to suppress LFO by changing the control parameters or control strategies of the converters. This paper presents a proposed scheme of suppressing LFO by applying a static synchronous compensator (STATCOM) to the traction network. The stability of the vehiclegrid system is first analyzed using the norm criterion. Next, for unstable vehicle-grid systems, the approach of utilizing a modular multilevel converter STATCOM (MMC-STATCOM) connected to the grid is proposed to suppress the LFO. Further, when the MMC-STATCOM is connected to the grid, the parameter sensitivity analysis is implemented in detail; the analysis results indicate that the MMC-STATCOM-based approach operates well in suppressing LFO, regardless of the change of the system parameters. The simulation results validate the stability analysis and the efficient suppression of LFO for the vehicle-grid system.