【作者】 许赟；

【导师】 邹云屏；

【作者基本信息】 华中科技大学 ， 电气工程， 2008， 博士

【摘要】 随着电力电子技术的不断发展,在高压大功率的用电领域,柔性交流输电、高压直流输电、高压大型电机的变频调速等都离不开大功率的电力电子装置。在实现高压大功率变换的几种解决方案中,多电平变换器由于具有减少器件的开关应力,优化输出波形,提高转换效率等优点,因而受到了较多关注。混合级联多电平作为多电平技术发展中的一项创新性技术,为高压大功率变换器的研制开辟了一条新思路。STATCOM的技术是基于变流器的FACTS技术的一个基础技术,因而本文在对混合多电平电路拓扑结构研究的基础上,对基于改进型混合级联多电平变换器的STATCOM进行研究。本文将从研究混合多电平的拓扑结构、调制方法、输出波形的频谱分析、控制系统到其在无功补偿中的应用这一思路进行系统的研究,以下是本文的主要研究工作:本文将众多的混合多电平拓扑结构进行归纳分析,给出了混合级联多电平基于并联和串联思想,以广义多电平半桥桥臂为基本单元的通用拓扑生成方法,按照该方法可以衍生出更多的混合多电平拓扑。同时根据目前混合多电平拓扑的特点和实际应用的要求,研究了一种颇具实用价值的改进型混合级联多电平变换器,该拓扑将具有相同的母线电压的一个二极管钳位H桥模块与若干个两电平H桥模块级联,通过阶梯波与多载波PWM调制相结合的混合调制方法得到输出电压。然后对调制方法进行数学上的分析,构建了三种常用载波分布下调制过程的三维数学模型,通过对模型的双Fourier级数展开和严格的数学推导,得到了在不同载波分布下输出电压的解析表达式,由此可知该变换器输出波形的完整的频谱信息。本文对传统混合级联多电平变换器中存在的直流侧功率倒灌现象进行研究,给出了改进型混合级联型多电平变换器在混合调制策略下保证不存在功率倒灌现象的阶梯波的调制方法。为了将该拓扑实际应用,本文设计了基于微处理器DSP与大规模集成电路FPGA相配合的控制系统结构,并通过使用重复控制设计了一台基于混合级联多电平拓扑的逆变器。本文分析了STATCOM进行无功补偿的原理,提出了一种基于改进型混合级联变换器的STATCOM的拓扑结构。根据级联多电平变换器可以分相对系统进行无功补偿的特点,采用无零序电流方案设计了三相STATCOM,分别对电网电压三相对称或不对称时,补偿平衡或者不平衡的三相无功电流进行仿真,证实了分相控制在这些情况下都有比较好的补偿效果,非常具有研究价值。随后通过对电流环的数字控制系统的分析,给出了P控制器的稳定范围,并通过对PI控制,直接重复控制、PI+重复复合控制的比较研究,得出了PI+重复复合控制可以使电流环拥有较好的系统响应速度的同时拥有较好的稳态性能。本文针对自适应滤波算法中常规的最小均方算法(LMS)应用于电流检测时期望的缺点,在分析该方法中自适应权值的变化规律的基础上,提出了两种有效的变步长LMS算法:即基于检测误差的相干平均值和基于重复思想去除重复出现的谐波电流干扰的思想来调节步长的变步长的LMS算法,并用仿真和试验进行了验证。更多还原

【Abstract】 With the development of the Power Electrical technology, the applications of high power PE devices in the high voltage high power field such as FACTS、HVDC、VFVS are more important than before. In the several solutions of high voltage high power transformation, the Multilevel Converter received wide attentions for its capability of increasing the output voltage magnitude and reducing the output voltage and current harmonic content, decreasing the switch frequency and the voltage of each power semiconductor. As an innovative technology, the hybrid multilevel converter brings a new way to the research of the high power converter. STATCOM is the basic technology of the FACTS technology; therefore based on the hybrid cascade multilevel converter’s topology research, a noval STATCOM of a hybrid cascade multilevel converter is particularly discussed. The order of the disquisition is from the topology’s structure to modulation, spectral analysis, control circuit and the application of the static var compensator. The followings are the main work:Analyzing of the numerous hybrid multilevel topologies, a universal generative topology is obtained by the parallel and series ways based on the generalized multilevel half bridge. By this method, more hybrid multilevel topologies can be derived from it. From the hybrid multilevel converter’s characters and the commands of the actual application, a valuable improved hybrid cascade multilevel converter is presented. This proposed converter is the series-connection of a Neutral-Point-Clamped (NPC) converter and several common H-bridge converters with equal dc bus voltage, and by a hybrid modulation method which incorporates square-wave synthesis in conjunction with unipolar triangle carried-based PWM method the output voltage wave is obtained. Based on the anatomy of hybrid modulation process in nature, 3-D mathematic models are built about three kinds of carrier dispositions frequently. Further, by double Fourier series expansion and intricate derivation, strict output analytic solution is acquired. The output analytical solution contains all original informations of the output waveform spectra.The problem of the power flow change in the cascade modules in the traditional hybrid cascade topology is considered, and the square waves’ modulation ranges which ensure the converter don’t have the power flow change in the improved hybrid cascade multilevel converter’s hybrid modulation strategy is obtained. For the actual application of the topology, a based on FPGA-DSP control circuit is devised, and a hybrid cascade multilevel inverter is carried out by the repetitive control.After the reactive power compensation principle of the STATCOM is analyzed, a novel STATCOM structure based on the improved hybrid cascade multilevel converter is presented. In virtue of the separated phase character of the cascade topology, a reactive power compensation system is designed by the non-zero-order current mode to control. By this design, the simulations which included the conditons of the symmetry or asymmetry grid voltage and balance or unbalance reactive load current obtained good results, and is improved to be a valuable control method. Following the analyses of the digital current loop control system, a comparison research between the PI controller, the repetitive controller and their composite control method is presented, and the composite control based on the digital PI controller and the digital repetitive controller is proposed to improve the composition performance of the digital PI controller, when the repetitive controller enhancs the steady state performance, the PI controller ensuring dynamic performance.Through theoretically investigating into the convergence process of the two weighting factors in the adaptive harmonic filter, two novel algorithms are presented to modify the least mean square (LMS) algorithm. The first LMS algorithm update the step-size from the time-average of error signal and the second algorithm based on avoiding the repetive harmonic disturb to provide a fast convergence at early stages and ensure a small final maladjustment. Both of them can greatly shorten the transient period while keeping steady-state accuracy.更多还原