Transient Stability Enhancement and Voltage Support for Grid-Forming Converters via Adaptive Improved Observer Control Under Grid Fault

With the large-scale integration of renewable energy sources, grid-forming (GFM) converters with inherent voltage and frequency support capabilities have attracted significant attention. However, due to the limited overcurrent withstand capability of power electronic devices, the stable operation of GFM converters under grid faults such as grid voltage sags remains a critical challenge. To address this issue, this paper systematically investigates the mechanisms of power angle instability and overcurrent generation during grid faults by a unified equivalent impedance model. Based on this analysis, a comprehensive control strategy that simultaneously considers power angle stability and overcurrent suppression is proposed. By introducing an adaptive improved observer control (AIOC), the active power reference is adaptively adjusted to enhance the power angle stability of the system. Meanwhile, the voltage reference is dynamically regulated to effectively limit the fault current while enhancing the voltage support capability. Finally, comprehensive theoretical analysis and experimental validation are provided. The experimental results demonstrate that the proposed strategy is capable of ensuring power angle stability and limits the overcurrent to within 1.5 p.u. Meanwhile, the voltage magnitude is increased by approximately 6%. The results demonstrate the robustness and adaptability of the proposed method under various conditions.