Transient Stability Improvement of Grid-Forming Converters Through Voltage Amplitude Regulation and Reactive Power Injection

Grid-forming converters, which provide frequency and voltage support to the grid, have been identified as an enabling technology in modern power systems. However, the unstable operation of grid-forming converters under large disturbances poses a significant challenge. To address the challenge, this article presents an in-depth analysis of the transient stability of grid-forming converters and proposes two effective methods to improve their transient stability. First, it is revealed that the active power injection and absorption of grid-forming converters are asymmetrical. Subsequently, the methods of voltage amplitude regulation and reactive power injection are proposed to improve the transient stability of grid-forming converters. By means of phase portraits, the effect of transient stability improvement by the proposed methods are clearly described. Furthermore, a detailed quantitative analysis is performed, and the critical values of voltage amplitude and reactive power in transient periods are derived to guide controller design. Finally, simulation and experimental results are provided to validate the effectiveness of the proposed methods.