架空线模块化多电平换流器(modular multilevel converter, MMC)型直流电网亟需解决严重直流故障的快速隔离和清除问题。然而，目前混合式高压直流断路器普遍存在着切断时间和切断容量之间的矛盾，并最终转化为直流电抗器容量对直流电网稳态优质运行及暂态高效限流之间的矛盾。为此，申请人提出具备限流电抗阵列灵活重构能力的往复式直流断路器拓扑，可以从原理上实现稳态低电抗和暂态高限流电抗的灵活切换，并且具备了直接切断、限流后切断和限流后恢复等多运行模式，可以从原理上有效缓解目前存在的直流电抗容量的矛盾。在已有研究基础上，本项目将通过理论研究、方案设计、仿真和实验验证的思路，重点解决电压源型直流电网的暂稳态边界问题，揭示往复式直流断路器的电抗阵列重构机理和直流电网故障电流传播演变机理，提出以新型直流断路器主导的直流电网协调保护方法。

It has been a big issue that the dc-side short-circuit fault should be cleared promptly and reliably in the overhead line (OHL) modular multilevel converter based dc grid. However, the state-of-the-art hybrid dc circuit breakers (DCCB) face the contradiction of the breaking time and breaking capacity, which ultimately transferred to the contradiction of the dc reactor capacity on the premium steady state operation and efficient transient fault current limiting. Therefore, this applicant proposes a novel reciprocating hybrid DCCB topology which can flexibly reconstructing the dc current limiting reactors, and thus the DCCB can switch among the operation modes of direct breaking, current limiting then breaking and current limiting then recover, further the contradiction of the dc reactor capacity is relieved. Beginning from the research achievements, this project will follow the regular procedure of theoretical investigation, scheme design, simulation analysis and prototype experimental tests, focusing on the solution of voltage source based DC grid transient stability boundary problems, revealing the reactor array in reciprocating hybrid DCCB reconstructed mechanism and the fault current spreading principle in DC grid and proposing a novel DCCB dominated coordination protection scheme.