基于MMC的高压直流输电控制策略研究

发布时间：2018-04-30 16:47

本文选题：高压直流输电 + 模块化多电平换流器　；参考：《安徽理工大学》2017年硕士论文

【摘要】：传统两电平换流器(VSC)在高压直流输电(HVDC)领域越来越受到性能和电压等级的限制,而模块化多电平换流器(MMC)得益于其独特的拓扑结构,使它具有诸多其他低电平换流器无法媲美的优点,从而使MMC-HVDC技术在输电领域得到大力发展。本文从MMC拓扑结构、运行机制、调制技术、桥臂均压和环流抑制入手,提出一种改进的均压优化控制算法和基于记忆的环流抑制算法,相比于传统控制算法产生了有益效果。本文首先分析了 MMC主电路拓扑及运行机理,在此基础上阐述了三相MMC工作原理,主流调制策略。建立MMC的数学模型,分析其交流侧与直流侧电气量关系以及桥臂子模块电容和桥臂电感元件能量交换机制,并对MMC运行特性进行分析,进而揭示其控制原理,为后面章节研究坐标变换及控制策略奠定基础。其次在分析了子模块电容电压波动原理和桥臂环流产生机理的基础上,提出子模块均压和桥臂环流抑制策略。在均压控制研究中,介绍了以基于最近电平逼近调制(NLM)的电容电压排序法为代表的传统控制策略,在此基础上提出一种改进的均压优化算法,并在Matlab/Simulink平台中对两种方法的控制效果进行了仿真比较;在环流控制中,详细介绍了记忆控制原理,并将它应用于环流抑制器,与基于PI控制的传统环流抑制器进行了性能比较,并仿真分析。最后研究了 MMC-HVDC系统控制策略,主要搭建并对比了基于αβ两相静止坐标系下和dq两相旋转坐标系下的控制策略分别在稳态控制和交流系统暂态控制下的效果发挥。提出在αβ坐标系下采用比例谐振控制用于控制器的设计,并进行了仿真验证。针对稳态控制策略,分析比较了基于dq坐标系和αβ坐标系的数学模型,得出αβ坐标系下控制量无交叉耦合项的结论。据此设计了基于PR控制器的电流内环控制器,再搭配上基于PI控制的功率外环控制器,代替传统双PI控制器作为MMC-HVDC系统的稳态控制器;针对交流系统发生不对称故障时的暂态控制策略,运用对称分量法分别建立了 dq旋转坐标系和αβ静止坐标系下的正、负序分量的数学模型,提出在αβ坐标系下选择PR控制作为负序电流控制器,简化了控制器的结构。
[Abstract]:The traditional two-level converter (VSC) is more and more limited by its performance and voltage level in HVDC, while the modularized multilevel converter (MMC) benefits from its unique topology. It has many advantages that other low level converters can not be compared with each other, so that MMC-HVDC technology has been greatly developed in the field of transmission. Starting with MMC topology, operation mechanism, modulation technology, bridge arm voltage equalization and circulation suppression, this paper presents an improved equalizing voltage optimal control algorithm and a memory-based circulation suppression algorithm, which has a beneficial effect compared with the traditional control algorithm. In this paper, the topology and operation mechanism of MMC main circuit are analyzed, and the working principle and mainstream modulation strategy of three-phase MMC are described. The mathematical model of MMC is established, and the relationship between AC side and DC side, as well as the energy exchange mechanism of bridge arm module capacitance and bridge arm inductor is analyzed. The operation characteristics of MMC are analyzed, and the control principle is revealed. It lays a foundation for the later chapters to study coordinate transformation and control strategy. Secondly, based on the analysis of the principle of capacitance voltage fluctuation and the generation mechanism of the bridge arm circulation, the submodule voltage equalization and the bridge arm circulation suppression strategy are proposed. In the research of voltage sharing control, the traditional control strategy, which is based on the capacitor voltage ranking method based on the nearest level approach modulation (NLM), is introduced. On this basis, an improved equalizing voltage optimization algorithm is proposed. The control effects of the two methods are simulated and compared in the Matlab/Simulink platform. In the circulation control, the principle of memory control is introduced in detail, and applied to the circulation suppressor, and the performance of the traditional circulation suppressor based on Pi control is compared. And simulation analysis. Finally, the control strategy of MMC-HVDC system is studied, and the effect of the control strategy based on 伪尾 two-phase stationary coordinate system and dq-two-phase rotating coordinate system in steady state control and AC system transient control respectively is built and compared. The proportional resonance control is used in the design of the controller in 伪尾 coordinate system, and the simulation is carried out. According to the steady-state control strategy, the mathematical models based on dq coordinate system and 伪尾 coordinate system are analyzed and compared, and the conclusion that there is no cross-coupling term in 伪尾 coordinate system is obtained. According to this, the current inner loop controller based on PR controller is designed, and the power outer loop controller based on Pi control is used to replace the traditional double Pi controller as the steady state controller of MMC-HVDC system. In view of the transient control strategy in the case of asymmetric fault in AC system, the mathematical models of positive and negative sequence components in dq rotating coordinate system and 伪尾 stationary coordinate system are established by using symmetric component method, respectively. In the 伪尾 coordinate system, PR control is chosen as the negative sequence current controller, which simplifies the structure of the controller.
【学位授予单位】：安徽理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

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