A Transient Power Angle Analysis Method under Asymmetrical Grid Faults of GFM

With the increasing use of power electronic devices in power systems, grid-forming converters (GFM) are favored for their ability to provide inertia and damping to the power system. After a grid fault, the transient stability of a GFM will be greatly affected by its damping characteristics and power coupling, so the transient stability boundary of GFM cannot be accurately portrayed by the traditional synchronous motor analysis method; and the existing methods are mostly focused on the transient stability of GFM under symmetrical faults, and the transient stability of GFM under asymmetrical operating conditions is rarely mentioned. Therefore, this paper analyses the transient operating characteristics of the GFM by resolving its output power angle from a new perspective. Firstly, this paper adopts the KBM method in nonlinear vibration theory to analyze the GFM output power angle under different grid faults. Then, this paper analyses the error sources of the traditional KBM method and proposes an improved KBM method with damping correction. Finally, based on the MATLAB/Simulink simulation platform, this paper verifies that the proposed damping-corrected KBM method possesses better accuracy in GFM power angle resolution compared with the traditional KBM method, and verifies its effectiveness under asymmetric faults.