Impact of DC-Link Voltage Control on Transient Stability of PLL-Synchronized Voltage-Source Converters

This article analyzes the impact of dc-link voltage control on the transient stability of voltage-source converters (VSCs) with the phase-locked loop (PLL) based synchronization. By integrating the dynamic of the dc-link voltage control into that of PLL, a fourth-order nonlinear large-signal model, which represents the dynamic behavior of the synchronism under large disturbances, is established. Further, the transient stability of the PLL-synchronized VSC is evaluated by using phase portraits. It is revealed that, compared to the case with a constant dc-link voltage, the dc-link voltage control would jeopardize the transient stability of the PLL-synchronized VSC, especially in the weak grid condition. Next, the parametric effects of the dc-link voltage control on the transient stability are demonstrated, which shed clear insights into the controller design to enhance the transient stability of VSCs. Lastly, all the theoretical findings are validated by the experimental tests.