中文摘要：

提出一种多端口背靠背式直流–直流换流系统（multiport back-to-back,MB2B）。其内部由多个电压源型换流器（voltage source converters,VSC）组成,VSC交流侧均连接到MB2B内部公共交流母线。为了使MB2B具有联接不同电压等级直流线路的功能,MB2B内部采用变压器来匹配不同电压等级的直流线路。MB2B的每个端口均可独立调节其潮流。为了减少VSC运行损耗,MB2B内部交流系统运行频率取为工频。详细设计MB2B的稳态控制及故障下功率自动平衡控制。为验证该拓扑的可行性和安全性,在PSCAD/EMTDC上搭建由四端口MB2B构成的实验电网系统的仿真模型,并针对该实验系统进行黑启动、潮流调节、直流故障隔离以及故障下自动功率平衡等仿真。实验系统中所有的控制策略均不需要任何通讯。

英文摘要：

This paper proposed a multiport back-to-back dc-dc converting system （MB2B）. The multiport consists of multiple voltage source converters （VSC）, and an independent inner ac circuit, which is used to interconnect the ac side of multiple VSC converters. In order to enable multiport MB2B interconnecting multiple dc lines with different dc voltages, transformers are used for voltage matching of different voltage levels. Each port of the MB2B could control its power flow independently. In order to reduce the power loss of the VSC converters, the inner ac circuit is operated at the grid frequency. Controllers of each VSC converter and automatic power rebalance control of the grid were designed in this paper. A laboratory-scale four-terminal de grid constructed by a four-port MB2B is used to test the necessity, feasibility and security of the multi MB2B. Simulations of the start-up process, power flow control, dc fault isolation and automatic power rebalance validated the feasibility and advantages of the MB2B. All of the controllers in the de grid are achieved without requiring any telecommunication.