Transient voltage stability of power systems with virtual synchronous generators or grid-following converters: analysis and enhanced control

Abstract

With the global energy transition, power systems are replacing synchronous generators (SGs) with voltage source converters (VSCs), which has significant implications for transient voltage stability. Analyzing VSC’s effect and leveraging its flexibility to improve stability are key challenges. Therefore, this study selects virtual synchronous generator (VSG) control and constant-power grid-following (GFL) control as representative strategies for the two dominant VSC control (grid-forming (GFM) and GFL). Then, this study theoretically derives the active and reactive power demand characteristics of induction motors. Building on these characteristics, along with the power characteristics of different power sources, the influence mechanisms of VSG and GFL on the transient voltage stability are analyzed. Distinct from existing methods, this work provides a comprehensive explanation of how induction motor power dynamics shape transient voltage behavior. The results showed that the integration of VSG and GFL degrades the transient voltage stability, with GFL exhibiting a more pronounced adverse effect. To mitigate these issues, the interaction between the active and reactive power of VSG is considered and an improved VSG control strategy is proposed to enhance the transient voltage stability. In addition, an adaptive coordinated control strategy for active and reactive power of GFL is introduced. Finally, the validity of the mechanism analysis and the effectiveness of the proposed control strategies are verified on a simplified system of a real large-scale power grid using the PSCAD platform.