Low-Frequency Oscillation Analysis and Suppression Based on Improved PLL Structure for Vehicle-Grid System of High-speed Railways

Recently, the low-frequency oscillation (LFO) has occurred frequently in vehicle-grid system of high-speed railways. In this paper, the phase-locked loop (PLL) structure is enhanced to restrain the LFO of the vehicle-grid system, and the impedance mathematical model of the vehicle-grid system based on the improved PLL is bulit. Furthermore, the effectiveness of the improved PLL in suppressing the LFO is verified based on the generalized Nyquist stability criterion and the Starsim-based hardware-in-loop (HIL) platform. In addition, an improved impedance measurement method for single-phase system is proposed to verify the accuracy of the impedance mathematical model of rectifier based on the improvement of PLL. Compared with the previous dq impedance measurement method, the proposed method can effectively reduce the times of disturbance injection, simplifying the measurement procedure.