A dq-Frame Impedance Measurement Method based on Hilbert Transform for Single-Phase Vehicle-Grid System

The input or output impedance of the subsystem plays a vital role in the stability analysis of power electronics cascaded systems, such as the vehicle-grid system in high speed railway. This paper proposes an accurate dq-frame impedance measurement method for single-phase systems based on Hilbert transform, and solves the inaccuracy problem when the sweeping frequency is higher than the fundamental frequency. The simulations on a vehicle-grid system in high-speed railway, namely the RL circuit for grid and the converter for vehicle, verify that the proposed method achieves accurate impedance measured results at frequencies both lower and higher than the fundamental frequency, particularly until the half of the switching frequency in the converter model, which can provide the basis and reference for dq small-signal modeling and stability analysis of single-phase systems.