With the continuous development of power electronics technology, variable-speed offshore wind turbines that penetrated the grid system caused the problem of inertia reduction. This study investigates the frequency stability of synchronous, offshore wind-farm integration through a modular-multilevel-converter high-voltage direct-current (MMC–HVDC) transmission system. When full-scale converter wind turbines (type 4) penetrate the AC grid, the AC system debilitates, and it becomes difficult to maintain the AC system frequency stability. In this paper, we present an improved inertial-response-control method to solve this problem. The mathematical model of the synchronous generator is based on the swing equation and is theoretically derived by establishing a MMC–HVDC. Based on the above model, the inertia constant is analyzed using a model that integrates the MMC–HVDC and offshore synchronous generator. With the new improved control method, a more sensitive and accurate inertia index can be obtained using the formula related to the effective short-circuit ratio of the AC system. Moreover, it is advantageous to provide a more accurate inertial control evaluation for AC systems under various conditions. Furthermore, the impact of the MMC–HVDC on system safety is assessed based on the capacitor time constant. This simulation was implemented using the PSCAD/EMTDC platform.

中文翻译：

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改进 MMC-HVDC 控制策略以提高交流系统的频率支持

随着电力电子技术的不断发展，穿透电网系统的变速海上风力发电机组带来了惯性降低的问题。本研究通过模块化多电平转换器高压直流 (MMC-HVDC) 传输系统研究同步海上风电场集成的频率稳定性。当全尺寸变流器风电机组（类型4）进入交流电网时，交流系统衰弱，交流系统频率稳定性难以维持。在本文中，我们提出了一种改进的惯性响应控制方法来解决这个问题。同步发电机的数学模型基于摆动方程，通过建立 MMC-HVDC 理论上推导出来。基于上述模型，惯性常数使用集成 MMC-HVDC 和海上同步发电机的模型进行分析。通过新的改进控制方法，利用与交流系统有效短路比相关的公式，可以获得更灵敏、更准确的惯量指标。此外，在各种条件下为交流系统提供更准确的惯性控制评估是有利的。此外，基于电容器时间常数评估 MMC-HVDC 对系统安全的影响。该模拟是使用 PSCAD/EMTDC 平台实现的。在各种条件下为交流系统提供更准确的惯性控制评估是有利的。此外，基于电容器时间常数评估 MMC-HVDC 对系统安全的影响。该模拟是使用 PSCAD/EMTDC 平台实现的。在各种条件下为交流系统提供更准确的惯性控制评估是有利的。此外，基于电容器时间常数评估 MMC-HVDC 对系统安全的影响。该模拟是使用 PSCAD/EMTDC 平台实现的。