Fast, sensitive, and selective protection principles are one of the major challenges in the feasibility of modular multi-terminal (MMC) high voltage direct current (HVDC) grids. Rate of change of voltage (ROCOV) and transient-based solutions are the traditional and widely accepted protection principles. Despite the speed and practicality of these solutions, they generally suffer from sensitivity and selectivity issues, particularly when dealing with high-resistance faults and low-size current limiting inductors (CLIs). To improve upon these methods, this paper proposes a new primary protection method that utilizes a selective drop rate of fault-generated voltage traveling waves (TW) to detect internal DC line faults. This is achieved by a comprehensive analysis of the line-mode fault-generated voltage (LFGV) under various internal and external fault scenarios. As the key fault characteristics, the proposed method exploits the minimum points of initial LFGV and the corresponding time to form the basis of the proposed protection method. The effectiveness of this approach is evaluated using a four-terminal MMC-HVDC grid in PSCAD/EMTDC. Compared to ROCOV and transient-based solutions, the proposed method identifies internal faults up to 1250 Ω with fast response, while maintaining its practicality and independence to CLI size.

中文翻译：

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基于电压行波选择性下降率的MMC-HVDC电网无单元保护方法

快速、灵敏和选择性保护原理是模块化多端（MMC）高压直流（HVDC）电网可行性的主要挑战之一。电压变化率 (ROCOV) 和基于瞬态的解决方案是传统且广泛接受的保护原理。尽管这些解决方案速度快且实用，但它们通常会遇到灵敏度和选择性问题，特别是在处理高电阻故障和小尺寸限流电感器 (CLI) 时。为了改进这些方法，本文提出了一种新的初级保护方法，该方法利用故障产生的电压行波（TW）的选择性下降率来检测内部直流线路故障。这是通过对各种内部和外部故障情况下的线路模式故障产生电压（LFGV）进行综合分析来实现的。作为关键故障特征，该方法利用初始 LFGV 的极小点和相应时间来构成该保护方法的基础。使用 PSCAD/EMTDC 中的四端 MMC-HVDC 电网评估该方法的有效性。与 ROCOV 和基于瞬态的解决方案相比，所提出的方法可以快速响应地识别高达 1250 Ω 的内部故障，同时保持其实用性和与 CLI 尺寸的独立性。