电网电压不平衡状态下MMC控制策略研究

发布时间：2018-03-27 22:27

本文选题：模块化多电平换流器　切入点：环流抑制　出处：《山东大学》2017年硕士论文

【摘要】：随着电力电子器件技术的进步和控制技术的发展,新型全控性半导体器件IGBT开始应用于高压直流输电领域。自从1997年世界上首个使用电压换流技术的直流工程——赫尔斯扬实验工程投入运行以来,目前已有多个柔性直流工程应用于可再生能源并网、大功率电机驱动、分布式发电并网、城市电网供电等方面。模块化多电平换流器(Modular Multilevel Converter,MMC)是电压源换流器拓扑中的一种。与其他拓扑结构相比,MMC具有谐波含量低、输出波形质量高、扩展性好、冗余备份简单等优点。但是由于自身拓扑结构固有的缺陷,MMC具有其他传统两电平、三电平拓扑没有的环流问题;并且当系统发生故障时,由于存在反并联的续流二极管,MMC无法通过自身结构阻断直流侧电流。故研究MMC环流问题及故障下控制策略问题具有重要的理论意义和实际价值。之前对于MMC环流的研究主要集中在稳态下的情况,且对于电网电压不平衡时的控制较复杂,需要引入多个控制器。本文对以上两点进行了深入研究,主要研究内容包括以下几点:(1)提出了一种MMC-HVDC在电网电压不平衡状态下的内环电流计算方法和环流抑制方法。在αβ坐标系中设计了一个基于非理想PR控制器的内环电流控制方法。与现有的正序、负序分别控制的方法相比,该控制方法更为精确。同时对于电网电压不平衡时环流分量进行了细致分析,分析结果显示该情况下的环流将由正序、负序、零序分量构成。为了抑制以上各分量,设计了相应的准PR环流抑制控制器,该控制器不仅具有良好的控制效果,还可以适应电网频率的波动。(2)提出了 MMC-HVDC一种改进的控制方法。为了有效控制MMC-HVDC,交流侧电流、环流以及子模块电容电压需要综合考虑,其中交流侧电流为基频分量,环流为二倍频负序分量。现有的方法是将交流分量、环流分量分开控制;然而当电网电压不平衡时,交流侧电流包含正序、负序分量,环流包括二倍频正序、负序、零序分量,分开控制会导致控制器设计复杂,系统稳定性降低。因此,本文中提出的方法不需要分离以上各分量,能有效控制交流正序、负序分量及环流中各分量,降低了控制器设计的数量和难度。(3)本文提出的各方法都在仿真环境中得到了验证,证明了本文分析的正确性和控制策略的有效性,证明本文提出的改进控制策略可以应用于实践。
[Abstract]:With the development of power electronic device technology and control technology, A new type of fully controlled semiconductor device (IGBT) has been applied to HVDC transmission. Since 1997, the world's first DC project using voltage commutation technology, the Hulse project, has been put into operation. At present, many flexible DC projects have been applied to the grid connection of renewable energy, the drive of high power motor, and the grid connection of distributed generation. Modularized multilevel converter (Modular Multilevel converter MMC) is one of the voltage source converter topologies. Compared with other topologies, MMC has lower harmonic content, higher output waveform quality and better expansibility. Redundant backup is simple, but due to the inherent defects of its own topology, MMC has other traditional two-level, three-level topology has no circulation problem, and when the system failure, Due to the existence of anti-parallel recurrent diodes, the DC current can not be blocked by its own structure. Therefore, it is of great theoretical and practical value to study the MMC circulation problem and the control strategy under the fault. The former is of great theoretical and practical value for the MMC circulation. Most of the research is focused on the steady-state situation. And the control of voltage imbalance in power network is more complex, so it is necessary to introduce multiple controllers. In this paper, the above two points are deeply studied. The main research contents are as follows: 1) this paper presents a method to calculate the inner loop current and reduce the circulation of MMC-HVDC under the condition of voltage imbalance in the power system. An inner loop based on the non-ideal PR controller is designed in the 伪尾 coordinate system. Current control methods-positive sequence with existing, The negative sequence control method is more accurate than the negative sequence control method. At the same time, the circulation component is analyzed carefully when the voltage is unbalanced. The results show that the circulation in this case will be positive sequence, negative sequence, In order to suppress the above components, the corresponding quasi-PR loop suppression controller is designed, which not only has good control effect, but also has good control effect. In order to effectively control MMC-HVDC, AC side current, circulation and capacitor voltage of submodule need to be considered comprehensively, in which AC side current is the fundamental frequency component. The current method is to control the AC component and the circulation component separately. However, when the voltage of the grid is unbalanced, the AC side current contains the positive sequence, the negative sequence component, the circulation includes the second harmonic positive sequence, the negative sequence, the zero sequence component. Separate control will lead to the complexity of controller design and the decrease of system stability. Therefore, the method proposed in this paper does not need to separate the above components, and can effectively control the ac positive sequence, negative sequence components and components in the circulation. The number and difficulty of controller design are reduced. (3) all the methods proposed in this paper are verified in the simulation environment, and the correctness of the analysis and the effectiveness of the control strategy are proved. It is proved that the improved control strategy proposed in this paper can be applied to practice.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM46;TM732

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