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. Furthermore, impacts of PLL’s phase-lag characteristics on additional damping and restoring coefficients are evaluated with variation of grid strengths, operating points and PLL bandwidths to reveal the impact mechanism of PLL dynamic on stability of DVC in VSC. Finally, time-domain simulation and StarSim hardware-in-the-loop (HIL) experimental results are conducted to validate the aforesaid stability analysis.