中文摘要：

推导直流一直流自耦变压器（De／Deautotr ansformer，DCAUTO）内部交流系统的动态特性，设计直流自耦变压器的控制器，分析高压侧直流故障以及低压侧直流故障时，直流自耦变压器的响应特性，提出将MMCl、MMC3部分子模块改造为自阻型子模块以隔离高压侧直流故障及低变比时在MMC1、MMC3额外串联半桥子模块以隔离低压侧直流故障的方法，分析双向直流故障隔离能力对DCAUTO造价的影响，论文随后在PSCAD／EMTDC上搭建一个±320kV／＋500kV1000MwDCAUTO的仿真算例，验证所提控制器与故障隔离方法的正确性。以测试的DC／DC为例，常规DC／AC／DC技术所需要的换流器总容量为2000Mw，而DCAUTO技术仅需1020Mw换流器即具备DC／AC／DC技术的全部功能（包括双向直流故障隔离能力1。常规DC／AC／DC的损耗率约为1．8％，而DCAUTO的损耗率约为0．97％，在低、中变比下，DCAUTO具备取代DC／AC／DC的潜力。

英文摘要：

Dynamics of the internal AC circuit of DC/DC autotransformer （DC AUTO） was derived, then the controller for DC AUTO was proposed. DC fault response during high voltage side DC fault and low voltage side DC fault was analyzed. A method of replacing part of the submodules in MMC1 and MMC3 with self-blocking submodule was proposed to isolate high voltage side DC fault, and a method of cascading additional half-bridge submodules at MMC1 and MMC3 was proposed to isolate low voltage side DC fault. The impact of dc fault isolating capability on converter cost of DC AUTO was analyzed. Technical feasibility of the proposed controller and DC fault isolation method were verified by simulations on a ＋320 kV/＋＋_500 kV, 1 000 MW DC AUTO using PSCAD/ EMTDC. Results show that a DC AUTO with bidirectional DC fault isolating capability has all the functions as a conventional DC/AC/DC. For the simulated test DC AUTO, the DC/AC/DC technology requires total converter rating of 2 000MW while only 1 020 MW is required in DC AUTO. Power loss ratio of DC/AC/DC at full power condition is about 1.8% while it is only 0.97% for DC AUTO. The DC AUTO is promising to replace conventional DC/AC/DC technology at low and medium DC voltage stepping ratio.