【作者】 李鹏飞；

【导师】 郭春义； 贺之渊；

【作者基本信息】 华北电力大学(北京) ， 工程硕士（专业学位）， 2019， 硕士

【摘要】 基于电网换相换流器(line commutated converter,LCC)和电压源型换流器(voltage source converter,VSC)的混合直流输电技术结合了 LCC的经济优势和VSC的技术优势,在近年来逐渐成为直流输电领域的研究热点,具有广阔的发展前景。从常规直流工程系统升级改造的角度,考虑对现有的常规直流系统进行柔性化升级,将受端换流站升级为柔性直流换流站,从而构建混合直流输电系统,是一种较为经济可行的思路。论文从常规直流工程改造入手,在对比分析了各混合直流系统级拓扑方案与各种换流器拓扑方案的基础上,总结了几类VSC拓扑的综合特性,开展了适用于常规直流输电受端柔性化改造的VSC拓扑选取工作。介绍了由半桥子模块与全桥子模块组合的混合型模块化多电平换流器(modular multilevel converter,MMC)拓扑结构以及子模块数量的配置方法。提出一种将原有的常规直流系统受端站升级为柔性直流换流站的方案,将常规柔直换流阀替换为半桥全桥混合型MMC换流阀,保留并利用了原有的换流变压器,降低了改造成本。首先,针对常规直流工程改造的情况,分析研究了受端LCC改造成双极和对称双极MMC两种主回路拓扑结构,对各类MMC拓扑及其变种开展研究工作,全面分析了各类MMC拓扑结构的技术特性以及在经济方面的优劣性,对适用于常规直流输电柔性化改造的受端站拓扑方案开展针对性的选取工作。其次,在确定系统主回路拓扑与受端站拓扑方案的基础上,介绍一种受端站拓扑方案——半桥全桥混合MMC的拓扑结构与工作原理,并介绍子模块数目的配置方法。再次,针对±500kV/3000MW等级的直流输电系统进行研究,介绍了直流输电系统主参数设计方法。包括主回路电流计算,子模块数量计算、子模块电容设计,桥臂电抗设计等。最后,利用半桥—全桥混合型MMC的过调制运行能力,提出一种常规直流工程受端站柔性化改造方案,并对所提出的方案进行主回路参数设计。结果表明,所提出的改造方案能够实现保留系统原换流变压器的柔性化改造,显著降低系统改造成本。在PSCAD/EMTDC环境下建立了相关仿真模型,仿真结果验证了该方案的可行性和主回路参数设计的正确性。更多还原

【Abstract】 Hybrid DC transmission technology based on line commutated converter(LCC)and voltage source converter(VSC)combines the economic advantages of LCC with the technical advantages of VSC,and has gradually become a Research hotspots in the field of direct current transmission have broad prospects for development.From the perspective of upgrading and reforming the conventional DC engineering system,considering the flexible transformation of the existing conventional DC system,it is more economical and feasible to transform the receiving end converter station into a flexible DC converter station to form a hybrid DC transmission system.Ideas.Based on the analysis of conventional DC engineering,the paper summarizes the hybrid DC system-level topology and various converter topology schemes,summarizes the comprehensive characteristics of several types of VSC topologies,and applies the conventional DC transmission receiving end.Flexible transformation of VSC topology selection work.The half-bridge-full-bridge hybrid modular multilevel converter(MMC)topology and the number of submodules are described.A scheme for upgrading the original conventional DC system to a flexible DC converter station is proposed.The conventional soft-reverse converter valve is replaced by a half-bridge full-bridge hybrid MMC converter valve,which retains and utilizes the original Converter transformers reduce the cost of retrofitting.Firstly,for the case of conventional DC engineering transformation,the two main loop topologies of the LCC and the bipolar and symmetric bipolar MMC are analyzed and studied.The research work on various MMC topologies and their variants is carried out.and various types of MMC are comprehensively analyzed.The technical characteristics of the topology and the advantages and disadvantages of the economy,the targeted selection of the end station topology suitable for the conventional DC transmission flexibility transformation.Secondly,on the basis of determining the system main loop topology and the end station topology scheme,this paper introduces a topological structure and working principle of the end station topology scheme,half bridge full bridge hybrid MMC,and introduces the configuration method of the number of submodules.Thirdly,the research on the HVDC transmission system of ±500kV/3000MW class is carried out,and the main parameter design method of HVDC transmission system is introduced.Including main loop current calculation,sub-module quantity calculation,sub-module capacitance design,bridge arm reactance design,etc.Finally,using the overmodulation operation capability of the half-bridge-full-bridge hybrid MMC,a flexible transformation scheme for the conventional DC engineering receiving end station is proposed,and the main circuit parameters are designed for the proposed scheme.The results show that the proposed retrofit scheme can realize the flexible transformation of the original converter transformer of the retention system and significantly reduce the cost of system transformation.The simulation model is established in the PSCAD/EMTDC environment.The simulation results verify the feasibility of the scheme and the correctness of the main loop parameter design.更多还原