Multi-Swing PLL Synchronization Transient Stability of Grid-Connected Paralleled Converters

During grid faults, the grid-connected paralleled converter systems is susceptible to a phase-locked loop (PLL) synchronization transient instability. Most existing studies focus on first-swing transient stability analysis using the equal-area criterion. However, achieving first-swing transient stability does not guarantee overall stability, as the system may still experience multi-swing transient instability. This paper analyzes the type of multi-swing transient instability issue from two aspects: transient instability mechanism and transient stability assessment. Firstly, the mechanism of multi-swing transient instability is revealed from the transient energy conversion point of view. Then, considering transient interactions between converters, the largest estimated domain of attraction (LEDA) is constructed utilizing the Takagi-Sugeno method. Using the LEDA, the multi-swing transient instability problem of the grid-connected paralleled converter systems is quantitatively analyzed. Finally, the theoretical results are verified based on the RT-LAB hardware-in-the-loop experimental platform.