MMC-HVDC直流线路故障分析与保护策略研究

发布时间：2018-09-11 21:05

【摘要】：模块化多电平换流器(modular multilevel converter,MMC)的高压直流输电技术由于其换流器的结构特性,所以具有高度模块化、谐波含量低及调控灵活的优势,因此,在电网领域中得到了广泛的应用。目前,MMC-HVDC系统的交流侧故障是国内外研究的侧重点,而对于系统直流输电线路的故障特性方面的研究较少。因此,本文主要内容是对MMC-HVDC系统直流输电线路上的故障特性及其保护策略的研究分析,其内容结构如下:首先,叙述直流输电技术的研究背景及现状,可知柔性直流输电技术对解决分布式能源并网、风电场并网、海上作业平台供电、以及对偏远无源地区等供配电场合的问题,具有较高的可行性和经济性,对创建绿色、清洁的电网具有重要的价值和意义。其次,对MMC-HVDC系统的拓扑结构和工作原理、系统的调制方式、子模块电容均压控制和MMC-HVDC系统的控制体系结构进行研究分析,这为MMC-HVDC系统控制策略的分析及其系统的建模提供了理论基础与依据。然后,针对MMC-HVDC系统的换流器级控制,依次对直接电流控制、启动控制和相间环流控制,利用建立数学模型的方法对这三种控制策略作了理论的分析和研究。并在PSCAD/EMTDC的仿真软件上,搭建了相应的控制器模型,由仿真结果表明系统控制策略及搭建模型的正确性。最后,针对直流输电线路上的单极接地故障、双极短路故障和断线故障,从其故障机理进行分析和研究,对单极接地故障提出,通过设定不同的交直流侧的保护定值和增大故障极线路的绝缘性的保护策略;对于双极短路故障提出,故障时利用过电流抑制策略、闭锁换流器和跳开交流断路器的保护策略;对于断线故障,提出通过改变换流站的控制方式的保护策略;最后通过仿真验证其保护策略的有效性。
[Abstract]:The high voltage direct current (HVDC) transmission technology of modular multilevel converter (modular multilevel converter,MMC) has the advantages of high modularity, low harmonic content and flexible control, so it has been widely used in the field of power network. At present, the AC side fault of MMC-HVDC system is the focus of research at home and abroad, but the research on fault characteristics of HVDC transmission line is less. Therefore, the main content of this paper is to study and analyze the fault characteristics and protection strategies of HVDC transmission lines in MMC-HVDC system. The content structure is as follows: firstly, the background and current situation of HVDC transmission technology are described. It can be seen that flexible direct current transmission technology has high feasibility and economy to solve the problems of distributed energy grid, wind farm grid, offshore platform power supply, and remote and passive areas. Clean power grid has important value and significance. Secondly, the topology and working principle of MMC-HVDC system, the modulation mode of the system, the capacitive voltage sharing control of sub-module and the control system structure of MMC-HVDC system are studied and analyzed. This provides a theoretical basis for the analysis of the control strategy of MMC-HVDC system and the modeling of the system. Then, aiming at the converter level control of MMC-HVDC system, direct current control, startup control and interphase circulation control, the three control strategies are analyzed and studied theoretically by the method of establishing mathematical model. Based on the simulation software of PSCAD/EMTDC, the corresponding controller model is built. The simulation results show that the control strategy and the model are correct. Finally, according to the single pole grounding fault, bipolar short circuit fault and break line fault on HVDC transmission line, the fault mechanism is analyzed and studied, and the unipolar grounding fault is put forward. By setting different protection settings of AC / DC side and increasing insulation of fault pole line, for bipolar short circuit fault, overcurrent suppression strategy, locking converter and skip AC circuit breaker protection strategy are put forward in the case of bipolar short circuit fault. The protection strategy by changing the control mode of the converter station is proposed for the fault line break, and the effectiveness of the protection strategy is verified by simulation.
【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;TM755

【参考文献】