基于电压源型的柔性直流输电系统（VSC-HVDC）在远海风能馈入中广泛应用。未来远海风能经多端柔直馈入的同时，给岸上电网频率稳定带来一系列挑战：缺乏有效的多端直流扰动模型及稳定判据；缺乏改善电网频率的控制措施。因此，研究适用于多端直流的扰动分析模型，并利用远海风机和VSC-HVDC的快速功率调节特性增强电网频率稳定，具有深远的理论意义和工程实用价值。首先，本项目拟借助线性控制理论建立多端直流的扰动模型；给出电压下垂控制下，多端直流系统的稳定运行判据。其次，通过对多端直流各端口功率耦合机理分析，构建直流控制变量与直流端口功率间的关联耦合矩阵；通过矩阵变换，给出改善岸上电网频率的直流附加功率解耦控制方法。最后，基于多端直流扰动模型，考查海上风场提供功率支撑的能力；通过对海上风场引入直流电压反馈，沟通风机转子动能与岸上电网扰动间通道；给出不依赖通信，改善岸上电网频率的海上风场与多端直流协同控制。

Voltage source converter based HVDC (VSC-HVDC) system is widely applied into offshore wind energy integration. With more offshore wind power integration via multi-terminal DC (MTDC) grid, it brings big challenges to the power system frequency stability. For instance, it lacks of the dynamic modeling of MTDC grid and the stability criteria. It lacks of the cooperative control to improve the power system frequency stability. Therefore, research on the dynamic modeling of multi-terminal DC grid and enhancing the power system frequency stability based on the fast power regulation of wind turbine and VSC-HVDC system has propounding theoretical value and industrial application potential. Firstly, this project aims to build the dynamic model of MTDC grid using linear control theory, and the stability criteria based on the DC voltage droop control. Furthermore, through the power coupling mechanism analysis of each DC terminal, this project constitutes the coupling matrix between the control variables of DC system and the DC terminal power. Based on the matrix transformation, an additional DC power decoupling control method is proposed to improve the onshore AC grid frequency stability. Lastly, based on the dynamic model of multi-terminal DC grid, the frequency support stability of wind turbines is evaluated. A communication-free cooperative control scheme of offshore wind farms and multi-terminal DC grid is proposed to improve the onshore AC grid frequency stability. This is achieved by detecting the DC voltage variation of offshore wind farm, and constituting the channel between rotor kinetic energy of wind turbine and onshore grid disturbances.