模块化多电平换流器及其控制技术研究

发布时间：2018-05-31 20:40

本文选题：模块化多电平换流器 + 直流输电　；参考：《哈尔滨工业大学》2017年博士论文

【摘要】：模块化多电平换流器与传统的多电平变换器拓扑相比较,展现出诸多优异的性能,例如其电压等级与功率等级可以达到±400kV/500MW以上、转换效率高于99%、模块化结构、扩展容易、可靠性高以及输出电压波形质量好等。这些优点使模块化多电平换流器具有广阔的应用前景,成为了近年来国际电力电子领域研究中最热点的课题之一,并已在柔性直流输电领域获得了初步应用,极大地推动了离岸风力发电系统的建设。与此同时,人们也开始研究能否将模块化多电平换流器拓展到大功率电机变频器等其他中高压电力电子应用当中。但是由于模块化多电平换流器是一种相对新兴的拓扑结构,目前对其调制、能量分布等基本理论的认识还不够全面,导致不能彻底分析并优化其工作性能。另一方面,模块化多电平换流器在启动预充电、子模块故障保护、电容电压波动抑制技术等方面也仍存在着一系列技术困难。在此背景下,本文首先从模块化多电平换流器的基本运行原理出发,对其载波移相调制进行傅里叶分析,发现了载波移相角对电压电流谐波特性的影响规律,并对应提出了优化的移相角选取方法。另一方面,通过对换流器内部功率传递机理的分析,从理论上解释了模块化多电平换流器电容电压平衡的控制依据,进而设计了分层解耦的平衡控制器。最后建设了完备的模块化多电平换流器实验平台,并介绍了平台中各部分软硬件的结构参数。论文其次针对模块化多电平换流器的启动与子模块故障这两种特殊工作情况进行研究。分析了模块化多电平换流器特有的子模块电容器启动预充电问题,在此基础上分别对直流侧启动与交流侧启动提出闭环恒流充电方法,可有效缩短启动时间、避免充电过程中的电流浪涌。对比了模块化多电平换流器子模块冷备用与热备用两种不同冗余机制的优缺点,分析了不同冗余机制下子模块故障后的电路特征,提出了完整的故障诊断与穿越控制方法。以上所提方案均在实验样机上进行了详细的实验验证。制约模块化多电平换流器广泛应用的一个瓶颈问题是子模块中需要昂贵笨重的高压大容量电容器作为功率支撑元件,以限制电容电压波动不超出允许范围。因此,如何降低电容器容量成为了降低换流器成本、体积以及变频器应用中驱动电机低速运行的关键问题。本文通过对子模块的连接形式进行优化,提出了改进型换流器结构,其中顶层、底层以及中间子模块的电容电压波动可显著降低,并提出了二倍频电容电压波动抑制的控制方案。而对于更为严重的基频波动,研究发现可通过降低直流母线电压的方式予以抑制,进而提出在模块化多电平换流器的直流母线上引入串联开关,结合适当的电流控制,可有效降低直流母线电压平均值,大幅抑制子模块电容电压的基频波动。以上波动抑制方案均在实验样机上进行了详细的实验验证,具有一定的工程应用前景。基于以上所提出的运行控制方法,论文最后进一步对模块化多电平换流器的衍生结构进行研究,旨在拓展其应用范围。首先提出将模块化多电平换流器应用为串联型直流输电分接装置,采用全桥型子模块结构,可有效解决直流线路附近村庄或小城镇的供电问题。同时该结构仅需较少的元件数量,具备很高的转换效率与可靠性。进一步地,通过将两组模块化多电平换流器构建成面对面结构,作为直流潮流控制器,能够解决未来直流电网中环路潮流不可控的问题。最后介绍了基于模块化多电平换流器的直流融冰装置,指出其相比于传统晶闸管型融冰装置展现出的技术优势,并提出了子模块电容电压的优化控制方法以及无覆冰天气下的STATCOM运行模式,最大程度地利用了该装置的安装容量。这一部分研究均得到了仿真或实验上的验证,为模块化多电平换流器的扩展提供了新的理论借鉴。
[Abstract]:The modular multilevel converter is compared with the traditional multilevel converter topology, showing many excellent performances, such as its voltage level and power level can reach more than 400kV/500MW, conversion efficiency is higher than 99%, modularization structure, easy expansion, high reliability and good output voltage waveform quality. These advantages make the modular much more. Level converter has a broad application prospect. It has become one of the most hot topics in the field of international power electronics research in recent years. It has been applied in the field of flexible direct current transmission. It has greatly promoted the construction of offshore wind power generation system. At the same time, people have begun to study whether the modular multilevel converter can be expanded. However, because the modularized multilevel converter is a relatively new topology, the basic theory of its modulation and energy distribution is not fully understood at present, which leads to the failure to thoroughly analyze and optimize its performance. On the other hand, modularized multi electricity. The flat converter still has a series of technical difficulties in starting precharge, submodule fault protection and capacitive voltage fluctuation suppression technology. Under this background, this paper first starts from the basic operation principle of modularized multilevel converter, and carries out Fu Liye analysis on its carrier phase shift modulation, and finds the carrier phase shift angle to voltage power. On the other hand, the control basis of the capacitive voltage balance of modularized multilevel converter is explained theoretically by analyzing the mechanism of power transfer inside the converter, and then a balanced decoupling controller is designed. Finally, the complete construction is built. The modular multilevel converter experimental platform is introduced, and the hardware and software structure parameters of each part of the platform are introduced. Secondly, the paper studies the two special work conditions of the starting and sub module failures of modularized multilevel converter. A closed loop constant current charging method is proposed on the basis of DC side start and AC side start, which can effectively shorten the start time and avoid the current surge during the charging process. Compared the advantages and disadvantages of two different redundancy mechanisms of the modular multilevel converter sub module cold standby and hot standby, the paper analyzes the different redundant mechanism after the failure of the module. A complete fault diagnosis and crossing control method is proposed. All the above schemes have been tested on the experimental prototype. A bottleneck problem that restricts the extensive application of the modular multilevel converter is that the expensive and heavy HV large capacity capacitor is required as a power support element in the sub module. The capacitance voltage fluctuation does not exceed the allowable range. Therefore, how to reduce the capacity of the capacitor becomes the key problem of reducing the cost, volume and the low speed running of the motor in the application of the inverter. This paper optimizes the connection form of the sub module, and puts forward the structure of the improved converter, the top layer, the bottom layer and the middle submode. The capacitance voltage fluctuation can be reduced significantly, and the control scheme of the two frequency doubling capacitor voltage fluctuation suppression is proposed. For the more serious fundamental frequency fluctuation, it is found that it can be suppressed by reducing the DC bus voltage, and then the series switch is introduced on the DC bus of the modular multilevel converter. The current control can effectively reduce the average voltage of the DC bus voltage and greatly restrain the fundamental frequency fluctuation of the capacitance voltage of the sub module. All the above fluctuation suppression schemes have carried out detailed experimental verification on the experimental prototype, and have a certain engineering application prospect. Based on the above proposed operation control method, the thesis further further modularized multi electricity. The derivative structure of the flat converter is studied in order to expand its application range. First, the modular multilevel converter is applied to a series DC transmission connection device. The whole bridge submodule structure is used to effectively solve the power supply problems in the villages and small towns near the DC line. The high conversion efficiency and reliability are prepared. Further, by constructing the two modular multilevel converter into face structure as a DC power flow controller, it can solve the problem of uncontrollable flow power in the future DC power grid. Finally, the DC ice melting device based on modular multilevel converter is introduced. The technical advantages of the traditional thyristor type ice melting device are presented, and the optimal control method of the capacitance voltage of the sub module and the operation mode of the STATCOM without ice cover are put forward. The installation capacity of the device is used to the maximum extent. This part of the study has been verified by simulation or experiment, and the expansion of the modular multilevel converter. The exhibition provides a new theoretical reference.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM46

【相似文献】