School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150000, China

In a weak grid, grid-following converters are prone to oscillation instability due to the interaction between the phase-locked loop (PLL) and the grid impedance. However, the DC voltage synchronization control method in the grid-forming technology can achieve autonomous synchronization by utilizing DC dynamics to emulate generator power angle characteristics, offering enhanced stability. By comparing the generator rotor motion equation with the DC voltage synchronization control structure, this paper proposes an adaptive control strategy for the grid-following converter in a weak grid, considering DC synchronization characteristics. This strategy introduces the DC dynamic deviation into the PLL synchronization link and employs weight coefficient allocation to achieve coordinated integration of both methods, enabling the converter to possess the stability advantages of the grid-forming control in weak grids. On this basis, the weight coefficients are designed according to system damping characteristics, and their correlation with the grid impedance is revealed. Further, the adaptive parameter adjustment is realized by integrating the online impedance identification technology. The sequence impedance model analysis shows that the proposed strategy can effectively suppress the sub-synchronous oscillation of grid-following converters in weak grids. Finally, the effectiveness of the proposed method is verified through experiments.