【目的】柔性直流输电技术是远海大规模风电外送的首选技术方案。针对大规模海上风电经柔直并网导致的陆上交流电网惯量缺失与阻尼不足问题，本文提出一种多时间尺度协同惯量支撑策略。【方法】通过定量分析柔直系统中子模块电容的暂态支撑能力，提出一种基于解耦控制的电容能量调节构网控制策略。该策略通过动态调整每相投入的子模块数量，解除了子模块电容电压与直流母线电压的耦合关系，在维持直流电压稳定的前提下显著拓宽了子模块电容电压的运行范围与能量利用潜力。在此基础上，引入频率死区环节，设计以直流电压为媒介的多时间尺度协同惯量支撑策略，实现“小扰动电容优先、大扰动风机协同”的分级有序支撑。【结果】基于PSCAD/EMTDC的仿真结果表明，系统在负荷突增工况下的支撑效果明显弱于负荷突减工况。在相同负荷变化幅度下，负荷突减与负荷突增工况中陆上电网频率最大偏差分别降低了33.3%和20.0%。这一差异的核心原因在于桥臂子模块数量受限，从而导致子模块电容能量的释放裕度低于其吸收裕度。【结论】所提控制策略有效实现了柔直系统与海上风电场惯量支撑能量资源整合与优化利用；通过设计频率死区环节，实现了多支撑主体的协同惯量支撑，在保障系统频率稳定性的同时，有效避免了小扰动对海上风电场的影响，提升了海上风电柔直并网系统的频率特性。

[Objective] Modular multilevel converter based high-voltage direct current （MMC-HVDC） technology serves as the optimal technical solution for power transmission of large-scale far-offshore wind farms. The grid integration of large-scale offshore wind power via MMC-HVDC leads to insufficient inertia and damping deficiency in onshore AC power grids. To solve the above problems， this paper proposes a multi-time-scale coordinated inertia support strategy. [Methods] This paper quantitatively investigates the transient power support capability of sub-module capacitors in MMC-HVDC systems， and proposes a decoupling control-based capacitor energy regulation grid-forming control strategy. By dynamically adjusting the number of inserted sub-modules in each phase， the proposed strategy eliminates the coupling between sub-module capacitor voltage and DC bus voltage. While maintaining DC voltage stability， the operating range and energy utilization potential of sub-module capacitors are significantly expanded. On this basis， a frequency deadband link is introduced， and a multi-time-scale coordinated inertia support strategy with DC voltage as the intermediate medium is designed. The proposed strategy realizes hierarchical and orderly frequency support， which preferentially utilizes capacitor energy under small disturbances and adopts coordinated wind turbine participation under large disturbances. [Results] Simulation results based on PSCAD/EMTDC verify that the system achieves inferior support performance under sudden load increase conditions compared with sudden load decrease conditions. Under identical load variation amplitudes， the maximum frequency deviation of the onshore power grid is reduced by 33.3% and 20.0% under sudden load decrease and sudden load increase scenarios， respectively. The core reason for this performance difference is the quantity limitation of bridge arm sub-modules， which results in a lower energy release margin than the energy absorption margin of sub-module capacitors. [Conclusions] The proposed control strategy effectively integrates and optimizes the utilization of inertia support resources of MMC-HVDC systems and offshore wind farms. The adoption of the frequency deadband link enables coordinated inertia support from multiple support subjects. The proposed strategy not only ensures system frequency stability， but also isolates offshore wind farms from the impact of small disturbances， thereby improving the frequency dynamic performance of offshore wind power MMC-HVDC integrated grid systems.