Dynamic Phasor Modeling and Low-frequency Oscillation Analysis of Single-phase Vehicle-grid System

In practical operations, low-frequency oscillation (LFO) occurs and leads to converter blocking when multiple electrical rail vehicles at the platform are powered by the traction network. This paper proposes a small-signal model in state-space form for multiple vehicle-grid systems based on a dynamic phasor. This model uses the phasor amplitude and phase as variables to accurately describe the dynamics of the converter phase-domain control. An eigenvalue based-method is introduced to investigate the LFO with advantages of acquiring all oscillatory modes and analyzing participation factors. Two low-frequency dominant modes are identified by eigenvalues. Mode shape reveals that one of the modes involves the oscillations between the grid-connected converters and the traction network, and the other one involves the oscillations among these converters. Then the sensitivities of these two low-frequency modes to different system parameters are analyzed. Participation factors of system state variables, when the number of connected vehicle increases, are compared. Finally, the theoretical analysis is verified by nonlinear time-domain simulations and the modal analysis based on the estimation of signal parameters via the rotational invariance techniques (ESPRIT) method.