适用于常规直流改造的混合直流输电系统主电路拓扑研究

分析比较了适用于混合直流输电系统的2种主接线方式的优缺点，针对常规直流改造为混合直流的特点，指出了适用于常规直流改造为混合直流的主接线方式。针对柔性直流架空线路故障隔离困难的问题，分析对比了4种可行的处理方法，指出了每种方法的优缺点及适用场合，并指出了适用于常规直流改造为混合直流的架空线故障处理方法。结合上述架空线故障处理方法，分析总结了工程中可行的4种适用于常规直流改造为混合直流的拓扑结构，并提出了2种非对称子模块混合型混合直流输电拓扑结构。从技术性和经济性两方面对这6种拓扑结构进行了对比分析，并指出了每种拓扑结构的适用场合。

Research on circuit topology of hybrid HVDC system suitable for refurbishing existing LCC-HVDC

The advantages and disadvantages of two main connection schemes designed for hybrid HVDC(High Voltage Direct Current) system are analyzed and compared. According to the features of refurbishing the existing LCC-HVDC(Line Commutated Converter based HVDC) to hybrid HVDC, it is concluded that the bipolar connection scheme is more suitable. Considering the problem of the overhead line fault isolation in VSC-HVDC(Voltage Source Converter based HVDC) system, four feasible methods are analyzed and compared, the applicable occasions, merits and demerits of each method are analyzed, and the suitable methods for refurbishing LCC-HVDC to hybrid HVDC are pointed out. Combined with the above mentioned overhead line fault isolation method, four feasible topologies suitable for refurbishing LCC-HVDC to hybrid-HVDC are summarized, and two topologies of asymmetrical cell-hybrid MMC(Modular Multilevel Converter) are proposed. The applicable occasions of each topology are summarized by comparison in terms of technology and economy.