Bifurcation Analysis of PLL-Based Grid-Following VSC for Robust Transient Synchronization Stability

Abstract

The widespread integration of renewable energy sources with grid-following voltage source converters (VSCs) has introduced new challenges in synchronization stability of mod-ern power systems. Unlike synchronous generators in classical power systems, VSCs with a phase-locked loop (PLL) rely on grid voltage measurements for synchronization, making them particularly sensitive to significant grid disturbances. This paper investigates the transient synchronization stability of a PLL-based grid-following VSC subjected to symmetrical faults. A reduced-order generalized swing equation is used to analyze the dynamics of the PLL-based VSC system. Using bifurcation analysis, we examine here the existence and stability of the equilibria after faults and identify the critical fault-clearing conditions that can lead to the loss of synchronism. Moreover, time-domain simulations, validated against analytical predictions, demonstrate that symmetrical faults can cause rapid desynchronization and lead to system instability.