多端柔性直流系统具有高效性与经济性，非常适用于大规模新能源多站点接入。然而，直流系统相较于交流系统惯性更低，易受扰动影响，严重时甚至可能导致系统失稳。针对这一问题，提出了基于MMC等效子模块数的惯量控制法和虚拟储能元件惯量控制法。前者通过改变MMC调制过程中上、下桥臂等效投入的子模块数量，提升MMC直流侧等效子模块电容。后者通过在MMC外环功率控制中加入扰动补偿量，实现MMC直流侧虚拟储能的引入。在此基础上，提出了一种多端柔性直流系统惯量综合控制策略，通过对两种控制方法叠加使用，实现更优的扰动平抑效果。最后，在PSCAD/EMTDC中搭建了在运的南澳三端柔性直流系统模型，验证所提控制策略的有效性。结果表明，与未采用任何惯量控制策略以及采用单一惯量控制的系统相比，采用所提惯量控制策略在系统发生扰动后直流电压和有功功率波动的平抑效果最好。

The multi-terminal flexible DC system offers high efficiency and economic benefits, making it particularly suitable for large-scale integration of renewable energy from multiple sites. However, compared to AC systems, DC systems have lower inertia and are more susceptible to disturbances, which can lead to system instability in severe cases. To address this issue, this paper proposes two inertia control methods: the inertia control method based on the equivalent sub-module number of the modular multilevel converter （MMC） and the inertia control method using virtual energy storage elements. The first method increases the equivalent capacitance of the MMC DC side by adjusting the number of sub-modules contributed by the upper and lower arms during the modulation process of the MMC. The second method introduces virtual energy storage on the MMC DC side by adding disturbance compensation to the outer loop power control. Building upon these approaches, this paper presents an inertia integrated control strategy for multi-terminal flexible DC systems, achieving better disturbance suppression by combining both control methods. Finally, a three-terminal flexible DC system model based on Nan’Ao Three-Terminal MTDC System is developed in PSCAD/EMTDC to validate the effectiveness of the proposed control strategy. The results show that, compared to systems without any inertia control strategy or those employing a single inertia control method, the system with the proposed inertia control strategy demonstrates the best suppression of DC voltage and active power fluctuations following a disturbance.