【作者】 王亮；

【导师】 谭国俊；

【作者基本信息】 中国矿业大学 ， 电气工程， 2015， 硕士

【摘要】 模块化多电平变换器(Modular Multilevel Converter,MMC)因其具有公共直流母线的模块化拓扑结构的特点而被广泛应用于高压直流输电、电能质量治理以及电气传动等领域,因此对MMC及其控制策略的研究有着理论和工程意义。本文主要对MMC的相关控制策略进行研究,包括调制策略、子模块电容电压控制策略、内部环流抑制策略,本文还设计研制了一台MMC五电平的实验样机,并对本文采用的控制策略进行实验验证。介绍了MMC拓扑结构与常见的子模块结构,建立了MMC数学模型,研究了MMC运行控制规律;论述了适用于MMC的调制策略,分析了各种载波调制以及最近电平逼近调制的实现方法;重点研究和分析了输出相电压分别为五电平、九电平时载波移相调制的区别以及脉冲移相代替载波移相的可行性。从桥臂能量脉动变化规律入手,分析子模块电容电压波动规律,推导电容选取的原则;结合MMC拓扑结构和工作原理,研究了一种利用自身直流母线对悬浮电容预充电的方法;对传统排序法进行改进,采用一种基于双保持因子及排序电压上下限的优化排序法,在保证各子模块电容电压均衡的前提下有效降低开关器件的开关频率。分析了环流形成机理、环流的性质与作用;从桥臂功率脉动的角度出发分析了影响二倍频环流幅值的因素,推导了桥臂电感选取公式;研究了基于模块变动选择法的环流抑制策略,并将其与优化排序算法相结合,达到抑制环流、均衡电容电压、降低开关频率的目的。从主回路和控制系统两个角度研制了一台五电平MMC实验样机,主回路设计包括主要器件参数设计与选型,控制系统设计包括控制系统架构设计和程序设计;在所研制的MMC实验样机上对基于模块变动选择算法和优化排序算法的控制策略进行实验验证,实验结果表明该控制策略可以均衡子模块电容电压、降低开关频率、有效减小环流幅值,验证了上述控制策略的可行性与正确性。更多还原

【Abstract】 Modular Multilevel Converter(shorted for MMC)has been widely applied into HVDC, power quality control, electric drive and other fields due to its characteristic of modular topology of common DC bus, so the research on MMC and its control strategy is of theoretical and practical significance. The relevant control strategies of MMC are studied in this paper including modulation strategy, control strategy of sub-module capacitor voltage, suppressing strategy of internal circulation, a 5-level prototype is also developed and the control strategy adopted is verified.Topology and common sub-module structures of MMC are introduced, and then mathematical models of MMC are established as well as its regulation of operation control. Modulation strategy applied to the MMC is studied including carrier phase shifted(shorted for CPS), pulse phase shifted(shorted for PPS), nearest level modulation(shorted for NLM), which the CPS on the conditions of 5-level and 9-level output phase voltage is research focus. The feasibility of pulse phase shifted instead of carrier phase-shift is analyzed.Fluctuation of capacitor voltage in sub-module is analyzed from the variation of energy fluctuation of bridge arm, the principle of selecting capacitor is deduced. Combined with the topological structure and working principle of MMC, a method which flying capacitor can precharge with its DC bus is studied. The traditional sorting method is improved by using optimization sorting method of dual factors and voltage limit to balance capacitor voltage in sub-module, the frequency of switch device can be reduced in views of balancing capacitor voltage of sub-module.The mechanism, quality and functions of circulation formation are analyzed. The factors of influencing the magnitude of the doubling-frequency circulation are analyzed from the power fluctuation of bridge arm, and the formula of inductor selection of bridge arm is deduced. Strategy of circulating current suppression based on the module changing selection method is given to realize circulating current suppression, capacitor voltage balancing, switching frequency reduction combined with the optimized sorting algorithm.A 5-level MMC prototype is developed respectively from the main circuit and the control system. The main circuit includes the design and selection of main device parameters, the control system includes the design of architecture and programming of the system. The control strategy based on the algorithm of module changing selection and optimized sorting is tested and analyzed on the MMC-5L prototype.The experimental results show that sub-module capacitor voltage is balanced, switch frequency is reduced, and the circulating current amplitude is decreased effectively under the adopted control strategy, the feasibility of the control strategy is verified.更多还原