基于混合子模块的循环嵌套型模块化多电平换流器特性

摘要

模块化多电平换流器在柔性直流输电领域中已得到广泛的应用。针对传统半桥子模块无法清除直流侧故障的问题，许多具备直流故障阻断功能的新型子模块相继被提出，相比半桥子模块，这些新型子模块增加了额外的阻断器件，从而在电平数较多的情况下增加了换流器的损耗。而基于循环嵌套机理的模块化多电平换流器(NLMMC)拓扑具有高电平输出能力，结合该拓扑结构特点，提出一种混合子模块结构，应用到NLMMC之后，使该换流器在具有直流侧故障阻断能力的基础上，提高了电平输出能力，从而间接地减少了换流器的损耗。从该拓扑结构的工作原理入手，对该换流器的故障阻断机理和调制策略进行了分析，提出了分层电压平衡控制策略。最后通过PSCAD/EMTDC仿真平台搭建了仿真模型，对换流器的电平输出能力、损耗特性以及故障阻断能力进行了仿真验证。%Modular multilevel converter MMC has been widely applied in flexible high voltage direct current HVDC fields. In view of the problems that traditional half bridge sub-module HBSM cannot clear the DC side fault many new sub-modules with the ability of DC fault blocking have been proposed.Compared with half bridge sub-modules these new modules have additional blocking devices which increase the losses of converters in the case of huge output levels.The topology of nested-loop mechanism based MMC NLMMC has high level output ability and combined with the characteristics of topology structure a hybrid sub-module structure is put forward.Application to NLMMC shows that it gives the inverter not only the ability of DC fault blocking but also a high level output capacity which reduces the wastage of the converter indirectly.This paper starts with the working principle of the topology structure the modulation strategy is analyzed and a hierarchical voltage balance control strategy and the mechanism of fault blocking are discussed.Finally the capacity of level output loss features and ability of fault blocking are simulated through the PSCAD EMTDC simulation platform.