Broadband Stability Enhancement Method for Grid-Forming Converters Based on Frequency-Segmented Impedance Reshaping

Grid-forming (GFM) converters are critical supporting equipment for power systems with high penetration of renewable energy. However, their complex interactions with the grid can lead to broadband instability, posing a serious threat to system security and stable operation. This paper proposes a frequency-segmented impedance reshaping method with grid-strength adaptation. First, frequency-segmented impedance models are established to reveal the stability problems. Subsequently, an outer-loop low-frequency stabilizer based on frequency feedback damping is designed to reshape the positive damping characteristics in the low-frequency band, and an inner-loop high-frequency stabilizer based on point-of-common-coupling voltage feedforward is designed to reduce the impedance magnitude in the high-frequency band. Finally, an adaptive gain-scheduling mechanism incorporating a real-time short-circuit ratio (RSCR) index is introduced to dynamically adjust key parameters in response to grid strength variations. Frequency-domain and time-domain analysis demonstrate that the proposed method effectively enhances the broadband damping capability of the converter, providing a systematic design approach and a practical engineering solution to address broadband stability issues in GFM converters.