The high-voltage direct current (HVDC) grid has been recognized as an effective solution for renewable energy integration. Currently, two main development trends for HVDC grids are being studied: a DC breaker based HVDC grid and fault-blocking converter based HVDC grid. Although the former has a perfect performance for fault clearance, its development is still highly constrained by the cost and maturity of DC breakers. The latter can extinguish DC faults by the fault-blocking converters. Without using DC breakers, there is no bottleneck in its technical feasibility. Nevertheless, in fault scenarios, such types of HVDC grids will be blocked at length for air-deionization, which is its main drawback. The aim of this paper is to minimize its power interruption time, by optimizing protection coordination strategies. To cover the most complex cases, the overhead line applications, in which the reclosure actions are required to be implemented, are considered. In this paper, the protection requirements of HVDC grids are first discussed, then the benefits of fault-blocking modular multilevel converters (MMCs) and their fault features are analyzed. Based on this, a control function is designed to reduce the air-deionization time. To minimize the influence of the DC faults, a separation methodology for restarting the system is proposed. The effectiveness of the proposed protection coordination schemes is validated by PSCAD/EMTDC simulations.

中文翻译：

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用于架空线路应用的具有故障阻止模块化多电平转换器的HVDC电网的优化保护策略

高压直流（HVDC）电网已被公认为是可再生能源整合的有效解决方案。当前，正在研究HVDC电网的两个主要发展趋势：基于DC断路器的HVDC电网和基于故障阻止转换器的HVDC电网。尽管前者在清除故障方面具有完美的性能，但其发展仍然受到直流断路器的成本和成熟度的极大限制。后者可以通过故障阻止转换器消除直流故障。不使用直流断路器，其技术可行性就没有瓶颈。然而，在故障情况下，此类HVDC电网将被完全阻塞以进行空气去离子处理，这是其主要缺点。本文的目的是通过优化保护协调策略来最大程度地减少其电源中断时间。为了涵盖最复杂的情​​况，考虑需要实施重合闸措施的架空线应用。本文首先讨论了高压直流输电网络的保护要求，然后分析了故障闭锁模块化多电平转换器（MMC）的优势及其故障特征。基于此，设计了控制功能以减少空气去离子时间。为了最小化直流故障的影响，提出了一种重启系统的分离方法。PSCAD / EMTDC仿真验证了所提出的保护协调方案的有效性。然后分析了故障阻止模块化多电平转换器（MMC）的优势及其故障特征。基于此，设计了控制功能以减少空气去离子时间。为了最小化直流故障的影响，提出了一种重启系统的分离方法。PSCAD / EMTDC仿真验证了所提出的保护协调方案的有效性。然后分析了故障阻止模块化多电平转换器（MMC）的优势及其故障特征。基于此，设计了控制功能以减少空气去离子时间。为了最小化直流故障的影响，提出了一种重启系统的分离方法。PSCAD / EMTDC仿真验证了所提出的保护协调方案的有效性。