The Analysis and Calculation of Power Angle Dynamics in Grid Forming Converter Under Large Disturbances Based on KBM Asymptotic Method

Grid forming (GFM) control strategy has been increasingly used in grid-connected converters to regulate system frequency and mimic the inertia of synchronous generator. However, the description of its power angle dynamics under large disturbances is still lacking up to date, which may pose great challenges to stable operation and economic configuration of grid-connected converters in the future power system. To overcome the aforementioned obstacle, a Krylov-Bogoliubov-Mitropolsky (KBM) asymptotic method with the perturbation theory is presented first in this article to derive an analytical solution for power angle trajectory under large disturbances. Considering that the antiderivative problem is usually unsolvable due to the complicated perturbation function, a tailored integral method is further proposed to address this problem and simplify the final result, which facilitates the KBM asymptotic method to the analysis and calculation of power angle trajectory. As a result, an explicit and accurate time-domain expression is obtained, and it reveals the quantitative relationships between control parameters and dynamic characteristics, which may provide a good potential for system transient stability analysis and GFM converter design. In the end, the effectiveness and accuracy of the proposed method are verified by both simulations and control-hardware-in-loop experiments.