Effect of Voltage Loops with Different Structures of Virtual Synchronous Generators on Small-Signal Stability

As the penetration of power electronic technologies, such as renewable energy and Voltage Source Converter based High Voltage Direct Current (VSC-HVDC) transmission, continues to increase, the power system is witnessing a reduction in inertia and a decrease in system strength. In contrast to traditional grid-following control, The application of grid-forming (GFM) control in VSC-HVDC technology enables both largecapacity power transmission across regions and system support. The virtual synchronous generator (VSG) is a typical GFM control method. However, VSG, as a power electronic device, has a lower disturbance rejection capability compared to traditional synchronous generators. Therefore, studying its small-signal stability is of great significance. In this paper, small-signal models of grid-side converters are established for two voltage loop structures of VSG: with and without feedforward terms. By comparing the eigenvalues, the stability differences between the two structures under weak grid conditions are analyzed. Furthermore, by comparing the participation factors of the eigenvalues in both structures and analyzing the eigenvalue root trajectories with varying grid strength, it is demonstrated that the feedforward term in the voltage loop significantly enhances system stability and the feasibility of GFM control under weak grid conditions. Finally, simulations are conducted in PowerFactory to validate the outcomes of the theoretical analysis.