Transient Stability Analysis of Grid-Following VSCs Considering DC-Link Voltage Control

Renewable energy sources (RESs) are integrated into the grid through the grid-following voltage source converters (VSCs). In the transient stability assessment of grid-following VSCs, typically only the influence of PLL is considered, while the influence of DC-link voltage control (DVC) is ignored. However, DVC has a similar time scale to PLL, indicating that DVC inevitably affects the transient stability of VSCs. This paper proposes an equivalent swing equation for the grid-following VSC considering DVC so that the transient stability can be studied using the classic equal area criterion (EAC). Firstly, the existence condition of the equilibrium points is derived based on the proposed swing equation. Secondly, based on EAC, the instability mechanism and parameter influence characteristics are revealed, and the dynamics of DVC saturation and control mode switching processes are analyzed. Finally, the theoretical findings are verified by time-domain simulation and hardware-in-the-loop (HIL) experiments.