国标《电化学储能构网型变流器技术规范》（征求意见稿）对故障下构网型储能（grid-forming energy storage system， GFM-ESS）的长时间低电压耐受和暂态同步稳定能力提出了要求。为了量化表征该能力，提出了一种GFM-ESS长时间故障下保持电压源特性并维持同步稳定的参数可行域构建方法。首先设计了一种考虑电磁暂态过程的故障电流工程计算方法，提取电流暂态峰值和稳态交流分量作为电流约束。其次构造了计及GFM-ESS虚拟阻抗和等效阻尼系数的能量函数形成同步稳定约束，并结合有功功率参考可行范围构造了平衡点约束。在此基础上给出了GFM-ESS故障下维持电压源暂态同步稳定的参数集合表达式，进一步以有功功率参考和虚拟电抗为关键参数刻画可行域，实现了GFM-ESS稳定运行边界的量化表征。最后，从电网侧与设备侧定量分析了不同类型参数对可行域边界的影响与作用机理，并通过电磁暂态仿真验证了所构建可行域的有效性。

The national standard “Technical Specification for Grid-Forming Converters in Electrochemical Energy Storage Systems” (draft for comments) requires grid-forming energy storage system (GFM-ESS) to achieve long-duration low-voltage ride-through and transient synchronization stability under faults. To quantify this capability, a parameter feasible region construction method is proposed for maintaining voltage-source characteristics and synchronization stability under GFM-ESS sustained faults. Firstly, a fault-current engineering calculation method considering electromagnetic transient process is developed to obtain the transient current peak and steady-state AC component as current constraints. Then, an energy function incorporating virtual impedance and equivalent damping coefficient is constructed as the synchronization stability constraint, while the feasible active-power reference range is used as the equilibrium-point constraint. On this basis, an expression is derived for the parameter set that enables the GFM-ESS to maintain voltage-source transient synchronization stability under faults. The feasible region is further characterized using the active-power reference and virtual reactance as key parameters, thereby quantitatively determining the stable operating boundary of the GFM-ESS. Finally, the effects of various grid-side and device-side parameters on the feasible region boundaries, together with their underlying mechanisms, are quantitatively analyzed, and electromagnetic transient simulations are conducted to verify the effectiveness of the constructed feasible region.