Multi-terminal hybrid high-voltage direct current (HVDC) systems have been developed quickly in recent years in power transmission area. However, for voltage-source converter (VSC) stations in hybrid HVDC systems, no direct current (DC) filters are required. In addition, the DC reactor is also not installed at the line end because the DC fault can be limited by the converter itself. This means that the boundary element at the line end is absent, and the single-ended protections used in line commutated converter (LCC) based HVDC (LCC-HVDC) systems or VSC-HVDC systems cannot distinguish the fault line in multi-terminal hybrid HVDC systems. This paper proposes a novel single-ended DC protection strategy suitable for the multi-terminal hybrid HVDC system, which mainly applies the transient information and active injection concept to detect and distinguish the fault line. Compared with the single-ended protections used in LCC-HVDC and VSC-HVDC systems, the proposed protection strategy is not dependent on the line boundary element and is thus suitable for the multi-terminal hybrid HVDC system. The corresponding simulation cases based on power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) are carried out to verify the superiority of the proposed protection.

近年来，多端混合高压直流（HVDC）系统在输电领域得到迅速发展。然而，对于混合 HVDC 系统中的电压源换流器 (VSC) 站，不需要直流 (DC) 滤波器。此外，直流电抗器也没有安装在线路端，因为直流故障可以由变流器本身来限制。这意味着线路末端的边界元件不存在，基于线路换向变换器 (LCC) 的 HVDC (LCC-HVDC) 系统或 VSC-HVDC 系统中使用的单端保护无法区分多端混合中的故障线路高压直流系统。本文提出了一种适用于多端混合高压直流系统的新型单端直流保护策略，主要应用瞬态信息和主动注入概念来检测和区分故障线路。与 LCC-HVDC 和 VSC-HVDC 系统中使用的单端保护相比，所提出的保护策略不依赖于线路边界元素，因此适用于多端混合 HVDC 系统。相应的基于电力系统计算机辅助设计（PSCAD）/包括直流电（EMTDC）的电磁瞬变的仿真案例被执行，以验证所提出的保护的优越性。