Analysis of influence of virtual inertia of grid-forming converter on transient stability characteristics

Due to its different characteristics from traditional synchronous generator, grid-forming converter (GFM-converter) affects the transient characteristics of the system when it is linked to the power grid. The mathematical model of the GFM-converter is built to describe its dynamic characteristics. Then, the transient process of the GFM-converter is analyzed qualitatively with the power-angle curve. The phase diagram method is used to study quantitatively and verify the validity of the above qualitative analysis. Finally, the influence of virtual inertia JGFM on the transient response is analyzed. In the case that equilibrium point exists after fault, decreasing virtual inertia improves the transient stability of the GFM-converter by increasing the damping ratio. When the equilibrium point does not exist after fault, the increase of JGFM reduces the virtual power angle at the time of fault clearing, and the power imbalance degree of the GFM-converter is reduced, thus its transient stability performance is improved.