Impacts of Phase-Locked Loop Dynamic on the Stability of DC-Link Voltage Control in Voltage Source Converter Integrated to Weak Grid

This paper investigates the impact of phase-locked loop (PLL) dynamic on the stability of DC-link voltage control (DVC) in voltage source converter (VSC) attached to weak grid. To start with, a small signal model of VSC attached to weak grid in DVC timescale is presented for stability analysis. On the basis, the dynamic characteristics of VSC are analyzed from the perspective of damping and restoring components which can determine the stability. With considering PLL dynamic, it is found that PLL performs as a phase-lag regulation for DVC and generates additional negative damping component in weak grid, thus weakening the stability of VSC.

Index Terms— DC-link voltage control timescale, phase-locked loop (PLL), small signal stability, voltage source converter (VSC), weak grid.