Distribution of Power Impact Among Grid-Forming Devices

Grid-forming devices can provide frequency and voltage support and are considered crucial components of future power systems. However, their process of power impact distribution for frequency support remains unclear. This paper, based on the three-stage theory of synchronous generator power impact distribution, analyzes the similarities and differences in control structure and physical processes between grid-forming devices and synchronous generators. It concludes that the distribution of power impact for grid-forming devices involves only two stages: the immediate stage distribution is influenced by electrical distance, while the steady-state distribution is based on droop coefficients. The dynamic process of grid-forming devices is influenced by both virtual inertia and droop coefficients, in contrast to the second and third stages of synchronous generators, which are influenced by inertia and governor coefficients, respectively. Furthermore, the impact of inner-loop control in grid-forming devices on electrical distance calculation is analyzed, and it is pointed out that virtual impedance control can manipulate electrical distance and control the distribution of immediate stage. Finally, a two-machine, two-area interconnected system is established to validate the theoretical analysis through simulation.