MMC-HVDC运行特性分析及线路内部故障识别

发布时间：2018-04-10 07:33

本文选题：模块化多电平换流器型高压直流输电　切入点：故障暂态分析　出处：《昆明理工大学》2017年硕士论文

【摘要】：伴随着电力电子相关技术的发展,模块化多电平换流器(MMC)作为一种新型的多电平换流器拓扑结构,应用于高压直流输电领域后,具有诸多优点,形成了柔性直流输电的代表性技术。目前对MMC-HVDC的研究主要着重于控制设计方面,对MMC-HVDC保护和故障类仿真分析方面还需进一步的研究。本文采用电磁暂态仿真软件PSCAD/EMTDC搭建的MMC-HVDC仿真模型,分析了模块化多电平柔性直流输电系统整体运行情况,MMC换流器主要的拓扑结构和子模块运行机理,以及在现有MMC-HVDC输电系统保护策略的研究基础上分析了MMC-HVDC的调制和保护策略。对目前MMC换流器中经常采用的PWM调制策略进行分析,对基于PWM调制策略的MMC换流器进行仿真,仿真了不同电平数的换流器对输出波形信号的影响,验证MMC换流器滤除谐波的特性。同时还对MMC-HVDC系统保护策略,系统保护范围的划分进行了探讨,分析了基于断路器保护和基于换流器拓扑结构自清除故障能力的保护方案。研究对MMC-HVDC线路运行方式及故障识别有重要意义。在MMC-HVDC系统故障特性方面,充分考虑了线路频率阻抗特性、故障距离、过渡电阻等对故障暂态量的影响。给出了 MMC-HVDC系统仿真时子模块的个数、子模块的电容及MMC桥臂上的电抗计算过程。分析了双极故障情况下MMC子模块和直流线路单极接地故障下暂态电流的特性,并对系统直流侧单极接地故障和双极接地故障进行了仿真分析。在MMC-HVDC仿真的过程中增加了雷击故障,并对在MMC-HVDC系统中雷击产生的干扰和故障进行了仿真分析。基于此,提出了MMC-HVDC系统基于小波系数高低能量比的单端保护方法。在分析MMC直流侧阻抗频率特性后发现MMC换流器对故障信号中的高频成分具有明显的衰减作用,可以通过故障信号的波型特征和小波能量差异来实现交、直流侧故障的辨识,仿真验证该方法识别故障效果明显且有效。
[Abstract]:With the development of power electronic correlation technology, modularized multilevel converter (MMC), as a new topology of multilevel converter, has many advantages after it is applied in the field of HVDC transmission.The representative technology of flexible direct current transmission is formed.At present, the research of MMC-HVDC mainly focuses on control design, and further research on MMC-HVDC protection and fault class simulation is needed.In this paper, the MMC-HVDC simulation model based on the electromagnetic transient simulation software PSCAD/EMTDC is used to analyze the main topology and operation mechanism of the modularized multilevel flexible DC transmission system.The modulation and protection strategies of MMC-HVDC are analyzed on the basis of the existing protection strategies of MMC-HVDC transmission system.The PWM modulation strategy which is often used in MMC converter is analyzed. The MMC converter based on PWM modulation strategy is simulated, and the influence of different level converter on the output waveform signal is simulated.Verify the characteristics of MMC converter filter harmonic.At the same time, the protection strategy of MMC-HVDC system and the division of system protection range are discussed, and the protection scheme based on circuit breaker protection and self-clearing fault capability based on converter topology is analyzed.The research is of great significance to the operation mode and fault identification of MMC-HVDC line.In the aspect of fault characteristics of MMC-HVDC system, the effects of line frequency impedance, fault distance and transition resistance on fault transient are fully considered.The number of sub-modules, the capacitance of sub-modules and the reactance calculation process of MMC bridge arm in MMC-HVDC system simulation are given.In this paper, the characteristics of transient current in MMC submodule and unipolar grounding fault of DC line are analyzed, and the DC side unipolar grounding fault and bipolar grounding fault of the system are simulated and analyzed.In the process of MMC-HVDC simulation, the lightning strike fault is added, and the interference and fault caused by lightning strike in MMC-HVDC system are simulated and analyzed.Based on this, a single-end protection method based on high-low energy ratio of wavelet coefficients for MMC-HVDC system is proposed.After analyzing the impedance frequency characteristics of MMC DC side, it is found that the MMC converter has obvious attenuation effect on the high frequency component of the fault signal. The fault identification of AC and DC side can be realized by the wave type characteristic of the fault signal and the difference of wavelet energy.Simulation results show that the method is effective and effective.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

【参考文献】