适用于架空线路输电的新型双极MMC-HVDC拓扑

New Breed of Bipolar MMC-HVDC Topology for Overhead Line Transmission

在充分借鉴传统直流输电工程结线方式的基础上,提出了一种适用于架空线路输电的新型双极模块化多电平换流器型高压直流输电(MMC-HVDC)系统拓扑。该拓扑中换流器采用基于箝位双子模块的改进型模块化多电平换流器(MMC),接地极线从上下2个换流器串联构成的双极结构中间引出。重点分析了换流器在故障条件下的等值电路和直流闭锁机理,并设计了直流侧故障后的详细控制策略,并用PSCAD/EMTDC仿真软件验证了该系统拓扑的有效性和可行性。结果表明:双极拓扑具有运行方式灵活、系统可靠性高等优点;由于二极管反向阻断和箝位作用,换流器在封锁所有绝缘栅双极型晶体管(IGBT)触发脉冲后数ms内就能实现直流闭锁,因此无需交流断路器动作,仅依靠换流器自身动作就能抑制短路电流;所设计的控制时序可有效处理直流侧的故障,并在暂时性故障下帮助系统迅速重启动,减少系统停运时间。

We propose a new type of bipolar MMC-HVDC topology for overhead line transmission by referencing the traditional HVDC system topology.This topology adopts improved modular multilevel converters（MMC） based on clamp double sub-modules.The ground electrode is led from the junction center of the bipolar structure,which consists of up-and-down converters in series.Furthermore,the equivalent circuit during DC fault and the fault blocking mechanism are analyzed,a control strategy and action sequence of the converter under the DC fault is proposed,and the feasibility and validity of the bipolar system are verified by PSCAD/EMTDC simulations.Several results are obtained from the simulation：the bipolar topology offers many features such as flexible operation modes and high system reliability,etc.;Owing to reverse blocking and voltage clamping of diodes,the DC blocking capability is achieved within a few milliseconds after turning off all insulated gate bipolar transistors（IGBT）.Thus,the short circuit current can be limited just by converter actions without tripping AC circuit breakers.The suggested control sequence can efficiently handle the DC faults,and can help the system recover very quickly after a DC temporary fault which reduces the out-of-service time.