Stability Analysis Considering PLL Effects for Grid-Following Inverter by Complex Vector Control

This paper analyzes stability of a grid-following inverter by the complex vector control in αβ domain and by the PLL synchronization control in dq domain. It is known that the frequency transfer function of the PLL may affect mutual interactions between grid and line impedances. This paper analyzes frequency characteristics of the inverter based on the mixed-domain control for stability by the impedance method. Considering frequency coupling effects by the PLL control, it is found that the passivity of the inverter is violated and it may become unstable for a weak grid. This result is validated by analytical derivation, simulation, and experiment.