【目的】针对电网发生对称故障期间构网型逆变器出现的功角失稳和输出电流过载问题，提出一种基于功率指令约束的故障穿越策略。【方法】首先，建立基于下垂控制的构网型逆变器暂态模型，分析系统在电网电压跌落下的暂态特征，揭示功率指令对暂态稳定性的影响；其次，分析逆变器与电网之间的电路关系，辨识故障电流特征及其主要影响因素；最后，提出一种基于有功指令约束的故障穿越方法，该方法可重塑功角稳定性并限制故障电流。【结果】MATLAB/Simulink仿真结果证明了所提策略能有效提升功角稳定性，实现故障穿越。【结论】提出的基于功率指令约束的故障穿越策略仅需约束有功指令便能有效解决构网型逆变器在电网电压跌落期间的功角失稳和过电流问题，为提高可再生能源并网系统的故障穿越能力提供了可行方案。

[Objective] To address the issues of power angle instability and output current overload in grid-forming（GFM）inverter during symmetrical grid faults，this paper proposes a fault ride-through strategy based on power command constraints. [Methods] First，a transient model of a droop-controlled GFM inverter is established to analyze the transient characteristics of the system under grid voltage sag conditions，revealing the impact of power commands on transient stability. Second，based on the circuit relationship between the inverter and the grid，the characteristics of fault currents and their primary influencing factors are identified. Finally，a fault ride-through method based on active power command constraints is proposed，which only requires calculating and setting the active power command value to restore power angle stability and limit fault currents. [Conclusions] Simulations performed in MATLAB/Simulink demonstrate that the proposed strategy effectively enhances power angle stability，achieving fault ride-through. [Conclusions] The proposed fault ride-through strategy based on power command constraints effectively addresses power angle instability and overcurrent issues in GFM inverters during voltage sag by constraining active power commands，providing a feasible solution for enhancing the fault ride-through capability of renewable energy grid-connected systems.