MMC-MTDC输电系统直流侧故障的控制及保护策略研究

发布时间：2018-05-10 06:18

本文选题：多端直流输电系统 + 模块化多电平换流器　；参考：《兰州理工大学》2017年硕士论文

【摘要】：多端柔性直流输电技术尤其是以基于全控型器件的电压源换流器多端直流输电(Voltage Source Converter based Multi-Terminal Direct Current,VSC-MTDC)技术近年来受到各国重视并得以飞速发展,主要是由于其在功率的可控性和输电扩展性方面具有无可比拟的优势,多端柔性直流输电技术可在风电场联网、大电网互联以及孤岛供电中发挥其特点。从电压源换流器中发展而来的模块化多电平换流器(Modular Multilevel Converter,MMC)具备换流器容量大及损耗小等优点,因此本文以基于MMC换流站的多端直流输电系统(MMC-MTDC)为研究对象,对其各级控制方式、直流线路故障特性以及故障发生时的保护策略进行重点分析和研究。本文以三端MMC直流输电系统为例,对单个MMC换流站以及三端MMC直流输电系统的数学模型进行深入分析。在调制方式上选取最近电平逼近的方式,在站级控制方面,采用内环电流控制,外环为内环提供电流参考值得方式。在系统级控制方面,本文对比了不同的控制方式且基于对直流电压和功率需求的考量,选择了电压裕度控制,并在PSCAD/EMTDC中搭建了三端MMC直流输电系统的仿真模型,对此模型在正常运行以及主换流站因故退出运行这两种情况进行仿真研究。最后,本文针对MMC-MTDC系统的直流侧线路上的三种故障——单极接地故障、极间短路故障以及断线故障发生时的情形进行仿真,对每种故障的特性深入分析,然后提出了相应的保护策略使得系统稳定运行。经过在仿真软件PSCAD/EMTDC上的仿真结果表明本文所提出的电压裕度控制策略及所设计的控制器,能够让系统在功率需求有变动时自行转换各换流站的控制方式来平衡整个系统的有功功率,即时在主换流站退出运行时也能让剩余系统稳定运行维持供电;在直流侧故障发生时,电压裕度控制策略配合相应的保护策略也能让系统快速恢复稳定,消除故障带来的影响,提高了系统对于直流侧线路故障的处理能力。
[Abstract]:In recent years, the technology of multi-terminal flexible DC transmission, especially voltage source converter based on full-control devices, has been paid more and more attention to and developed rapidly in recent years. Because of its unparalleled advantages in power controllability and transmission expansibility, multi-terminal flexible direct current transmission technology can play its role in wind farm interconnection, large power grid interconnection and island power supply. The modular multilevel converter (Modular Multilevel converter) developed from the voltage source converter has the advantages of large capacity and low loss. Therefore, this paper takes the multiterminal DC transmission system based on the MMC converter station as the research object and its control methods at all levels. The fault characteristics and protection strategy of DC line are analyzed and studied. Taking the three-terminal MMC DC transmission system as an example, the mathematical models of a single MMC converter station and a three-terminal MMC DC transmission system are deeply analyzed in this paper. In the modulation mode, the nearest level approximation is selected. In the field of station level control, the inner loop current control is adopted, and the outer loop provides the current reference mode for the inner loop. In the aspect of system-level control, this paper compares different control methods and based on the consideration of DC voltage and power demand, selects voltage margin control, and builds the simulation model of three-terminal MMC HVDC transmission system in PSCAD/EMTDC. The model is simulated in normal operation and main converter station exit operation. Finally, this paper simulates three kinds of faults on DC side line of MMC-MTDC system, such as single-pole grounding fault, inter-pole short-circuit fault and break-line fault, and deeply analyzes the characteristics of each kind of fault. Then the corresponding protection strategy is put forward to make the system run stably. The simulation results on the simulation software PSCAD/EMTDC show that the proposed voltage margin control strategy and the controller designed in this paper. The system can balance the active power of the whole system by changing the control mode of each converter station when the power demand changes. Even when the main converter station is out of operation, it can make the remaining system run stably and maintain the power supply. When the DC side fault occurs, the voltage margin control strategy combined with the corresponding protection strategy can also make the system quickly restore stability, eliminate the influence of the fault, and improve the system's ability to deal with the DC side line fault.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

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