模块化多电平变流器输出电流及电压波形改善研究
发布时间：2019-03-20 15:43
【摘要】：近年来,随着电力电子技术在风力发电、轻型高压直流输电等领域的应用,高压大功率电力电子设备得到国内外学者的广泛关注。模块化多电平变流器(modular multilevel converters, MMC)因其结构模块化,采用子模块级联的形式,具有良好的扩展性、运行损耗低、输出波形质量好、良好的冗余容错性、可靠性好等诸多优点,被认为是未来最具备应用价值的高压大功率电力电子变换拓扑之一。本文研究了模块化多电平变流器的拓扑结构和基本工作原理,建立了MMC的数学模型,对MMC环流和电容电压波动进行了分析,阐述了目前常用的调制策略和工作特性,重点研究了最近电平逼近调制技术(nearest level modulation,NLM),NLM调制实现简便,控制系统计算量小,适合MMC电平数较多的场合,当MMC电平数较少时,最近电平逼近调制方式输出电流的波形质量差、谐波含量高且不能精确跟踪参考电流。针对最近电平逼近调制方式在中低压领域MMC中的应用,本文提出了一种改进的最近电平逼近调制策略,即采用电流滞环控制器对最近电平逼近调制结果进行修正,即在双闭环控制结构的基础上加入环流控制器、稳压控制器、均压控制器等附加控制器,附加控制器在主控制器计算出的上、下桥臂电压参考值的基础上加入一定的修正量。该调制策略易于实现,动态性能好,控制器计算量小,能够对参考电流进行良好的跟踪,降低了电流谐波含量,显著改善MMC输出电流波形。本文针对模块化多电平变流器子模块电容电压波动影响子模块参数选择及降低交流电压输出质量的问题,分析了子模块电容电压波动、环流及传输功率等物理量之间的关系；引入准比例谐振控制器和陷波器,通过对MMC内部环流控制来抑制MMC子模块电容电压波动,不需要进行传统的坐标变换,有效的减少了计算量,有利于控制器的简化设计,在保证MMC子模块参数设计不变的情况下,能够有效抑制MMC子模块电容电压波动,改善MMC输出的交流电压波形。本文在MMC应用于电力牵引系统、高压变频调速系统及其他中高压大功率等方面做出了有益的尝试。
[Abstract]:In recent years, with the application of power electronics technology in wind power generation, light HVDC transmission and other fields, high-voltage and high-power electronic equipment has been widely concerned by scholars at home and abroad. Modular multilevel converter (modular multilevel converters, MMC) has many advantages, such as modularization, adopting sub-module cascade, good expansibility, low running loss, good quality of output waveform, good redundancy and fault tolerance, good reliability, and many other advantages, such as good expansibility, low running loss, good output waveform quality, good redundancy and fault tolerance, good reliability and so on. It is considered to be one of the most valuable high-voltage and high-power electronic transformation topologies in the future. In this paper, the topological structure and basic working principle of modular multilevel converter are studied, the mathematical model of MMC is established, the MMC circulation and capacitance voltage fluctuation are analyzed, and the common modulation strategies and working characteristics are described. This paper focuses on the study of the nearest level approximation modulation technology (nearest level modulation,NLM), NLM modulation is easy to realize, the control system calculation is small, suitable for more MMC level, when the MMC level number is less, the control system is suitable for the situation of more level, when the number of MMC level is less. The output current of the nearest level approximation modulation mode has poor waveform quality, high harmonic content and can not accurately track the reference current. In view of the application of the nearest level approximation modulation method in the medium and low voltage domain MMC, an improved nearest level approximation modulation strategy is proposed in this paper, in which the current hysteresis controller is used to modify the nearest level approximation modulation result. On the basis of double closed loop control structure, an additional controller, such as loop controller, voltage regulator, equalizing controller and so on, is added. The additional controller adds a certain amount of correction on the basis of the reference value of the voltage of the lower arm and the upper part of the controller calculated by the main controller. This modulation strategy has the advantages of easy realization, good dynamic performance and low computational complexity. It can track the reference current well, reduce the harmonic content of the current, and improve the output current waveform of the MMC significantly. In this paper, the relationship among capacitance voltage fluctuation, current circulation and transmission power of modular multilevel converter sub-module is analyzed, which affects the parameter selection of sub-module and reduces the output quality of AC voltage, and analyzes the relationship among capacitance voltage fluctuation, circulating current and transmission power of sub-module. The quasi-proportional resonant controller and notch filter are introduced to restrain the capacitance voltage fluctuation of MMC sub-module by controlling the internal circulation of MMC. The traditional coordinate transformation is not necessary, and the calculation is reduced effectively, which is beneficial to the simplified design of the controller. The capacitance voltage fluctuation of the MMC sub-module can be effectively suppressed and the AC voltage waveform of the MMC output can be improved under the condition that the parameters of the MMC sub-module are not changed. This paper makes a beneficial attempt in the application of MMC in electric traction system, high voltage variable frequency speed regulation system and other medium and high voltage and high power systems.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM46
[Abstract]:In recent years, with the application of power electronics technology in wind power generation, light HVDC transmission and other fields, high-voltage and high-power electronic equipment has been widely concerned by scholars at home and abroad. Modular multilevel converter (modular multilevel converters, MMC) has many advantages, such as modularization, adopting sub-module cascade, good expansibility, low running loss, good quality of output waveform, good redundancy and fault tolerance, good reliability, and many other advantages, such as good expansibility, low running loss, good output waveform quality, good redundancy and fault tolerance, good reliability and so on. It is considered to be one of the most valuable high-voltage and high-power electronic transformation topologies in the future. In this paper, the topological structure and basic working principle of modular multilevel converter are studied, the mathematical model of MMC is established, the MMC circulation and capacitance voltage fluctuation are analyzed, and the common modulation strategies and working characteristics are described. This paper focuses on the study of the nearest level approximation modulation technology (nearest level modulation,NLM), NLM modulation is easy to realize, the control system calculation is small, suitable for more MMC level, when the MMC level number is less, the control system is suitable for the situation of more level, when the number of MMC level is less. The output current of the nearest level approximation modulation mode has poor waveform quality, high harmonic content and can not accurately track the reference current. In view of the application of the nearest level approximation modulation method in the medium and low voltage domain MMC, an improved nearest level approximation modulation strategy is proposed in this paper, in which the current hysteresis controller is used to modify the nearest level approximation modulation result. On the basis of double closed loop control structure, an additional controller, such as loop controller, voltage regulator, equalizing controller and so on, is added. The additional controller adds a certain amount of correction on the basis of the reference value of the voltage of the lower arm and the upper part of the controller calculated by the main controller. This modulation strategy has the advantages of easy realization, good dynamic performance and low computational complexity. It can track the reference current well, reduce the harmonic content of the current, and improve the output current waveform of the MMC significantly. In this paper, the relationship among capacitance voltage fluctuation, current circulation and transmission power of modular multilevel converter sub-module is analyzed, which affects the parameter selection of sub-module and reduces the output quality of AC voltage, and analyzes the relationship among capacitance voltage fluctuation, circulating current and transmission power of sub-module. The quasi-proportional resonant controller and notch filter are introduced to restrain the capacitance voltage fluctuation of MMC sub-module by controlling the internal circulation of MMC. The traditional coordinate transformation is not necessary, and the calculation is reduced effectively, which is beneficial to the simplified design of the controller. The capacitance voltage fluctuation of the MMC sub-module can be effectively suppressed and the AC voltage waveform of the MMC output can be improved under the condition that the parameters of the MMC sub-module are not changed. This paper makes a beneficial attempt in the application of MMC in electric traction system, high voltage variable frequency speed regulation system and other medium and high voltage and high power systems.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM46
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