In this article, a modified hybrid dc breaker and a half-bridge modular multilevel converter (MMC) are employed to interrupt the dc fault current in a high-voltage direct current transmission system. In the hybrid dc breaker, parallel to the main branch, a series connection of an energy-absorbing capacitor and a Thyristor stack is employed. When a dc fault current is recognized, the Thyristor stack is triggered and the load commutation switch in the main branch is turned off. In addition, in the fault clearing state, the MMC is programmed to generate zero voltages at all arms. Using this mechanism, a second-order RLC circuit with zero input is formed, and the fault current is cleared in a very short time. A freewheeling path is provided to bypass the dc line when the equivalent inductance seen from the dc line is large. In contrast to conventional approaches, the peak of dc fault current is limited to a specific limit and the necessity to ultrafast mechanical switches is avoided. In addition, the amplitude of arms currents and corresponding insulated-gate bipolar transistors are kept in the safe operating area. A detailed circuit analysis of the new method is given and design formulas are extracted. Simulation results are provided in PSCAD/EMTDC environment, and experimental results are presented for a scaled-down prototype.

中文翻译：

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半桥 MMC 和混合直流断路器共同阻断直流故障电流

在本文中，采用改进的混合直流断路器和半桥模块化多电平转换器 (MMC) 来中断高压直流输电系统中的直流故障电流。在与主支路并联的混合直流断路器中，采用了能量吸收电容器和晶闸管堆栈的串联连接。当识别出直流故障电流时，触发晶闸管堆栈并关闭主支路中的负载换向开关。此外，在故障清除状态下，MMC 被编程为在所有臂上产生零电压。利用这种机制，形成了一个零输入的二阶RLC电路，并在很短的时间内清除了故障电流。当从直流线路看到的等效电感很大时，提供了一个续流路径来绕过直流线路。与传统方法相比，直流故障电流的峰值被限制在一个特定的限度内，并且避免了超快速机械开关的必要性。此外，臂电流的幅度和相应的绝缘栅双极晶体管保持在安全工作区。给出了新方法的详细电路分析并提取了设计公式。在 PSCAD/EMTDC 环境中提供了仿真结果，并为缩小的原型提供了实验结果。给出了新方法的详细电路分析并提取了设计公式。在 PSCAD/EMTDC 环境中提供了仿真结果，并为缩小的原型提供了实验结果。给出了新方法的详细电路分析并提取了设计公式。在 PSCAD/EMTDC 环境中提供了仿真结果，并为缩小的原型提供了实验结果。