【作者】 吴智超；

【导师】 邹云屏；

【作者基本信息】 华中科技大学 ， 电力电子与电力传动， 2005， 硕士

【摘要】 近年来,多电平功率变换技术因其在高压大功率应用场合的广阔前景,已成为电力电子领域的研究热点。围绕多电平变换器,新型电路拓扑及相关调制策略层出不穷。无论从广度还是深度而言,多电平技术研究都得到极大推动。本文以传统多电平逆变器拓扑为起点,重点研究混合多电平逆变器拓扑及其调制方法,并且构建了调制过程的数学模型,进而解析复杂的输出波形。基于单相二极管钳位5 电平逆变器,本文研究了二极管钳位级联型拓扑。这种拓扑是将多个单相二极管钳位5 电平逆变单元串接,合成输出更多电平数的电压。本文定义了混合多电平拓扑、混合调制方法,随后介绍了一种新型的混合二极管钳位级联多电平逆变器。这种新型逆变器是将具有不同直流母线电压的多个二极管钳位多电平逆变器串联。本文详细分析了直流母线电压比值为2:1 的两单元级联拓扑,提出了适用于此拓扑的新型混合调制方法,并进行了试验验证。作为对单相二极管钳位多电平拓扑的简化,本文研究了一种新型的不对称5 电平逆变器。这种新型逆变器是将半桥二极管钳位逆变器和传统两电平半桥逆变器共享同一直流母线电压而获得。本文分析了这种拓扑采用的方波和消谐波PWM 结合的调制方法。在这种调制策略下,新型逆变器允许开关速度较快的器件和耐压值较高的器件协同工作。文章将这种逆变器与其它四种单相5 电平逆变器进行了比较,对整个方案进行了试验验证。输出电压频谱分析为逆变器系统优化设计提供重要的信息,这一工作可通过计算机仿真完成。但由于开关波形误差和DFT 算法的影响,仿真分析的效果取决于调制参数的选择,若要保证仿真精度,调制参数必须受特定限制。因此,仿真分析频谱存在适用范围不广的缺陷,而严格数学解析输出频谱无疑能够克服以上不足。本文基于对混合调制过程本质的剖析,建立了在三种常用载波分布下调制过程的三维模型。针对模型,通过双FOURIER 级数展开和繁琐的数学推导,求得了输出电压的严格解析表达式。所有解析表达包含了完整的原始输出波形频谱信息,文中总结了输出电压的频谱特性。从文中分析过程可以看出,这种方法得到的结果不仅适用于非过调制而且适用于过调制,不仅对同步调制成立而且对异步调制成立。并且这种分析方法为不同调制方式下的输出PWM 波形的频谱分析提供了一种启发性的思路。更多还原

【Abstract】 In recent years, multilevel power conversion technology has been becoming hot point in power electronic research due to extensive outlook in high power application. Novel topologies and modulation strategies concerning multilevel converters are emerging continuously. As far as the width and depth are concerned, research on multilevel technique is advanced greatly. To begin with traditional multilevel topologies, this paper focuses on topologies and modulation methods of hybrid multilevel inverters. Besides, mathematic models illustrating modulation process are constructed to parse complicated output waveforms. Based on single-phase diode-clamp 5-level inverter, diode-clamp cascaded multilevel inverter is presented. The topology consists of multiple single-phase diode-clamp 5-level units in series to synthesize more levels output. The concepts of hybrid multilevel topology and hybrid modulation method are defined clearly in the paper. As followed a new hybrid diode-clamp cascaded multilevel inverter is introduced. The inverter is based on connection of several diode-clamp inverter modules with different dc bus voltage values. An example is discussed in detail that two modules are linked with dc bus voltage 2:1. Also a new hybrid modulation method feasible in the inverter is put forward. Experiment validation is carried out. An asymmetric 5-level inverter is presented as simplification to single-phase diode-clamp multilevel topology, which is composed of a half-bridge diode-clamp inverter and a conventional half-bridge inverter in share with a common split-capacitor power supply. It is analyzed in the paper that square-wave operation combines with subharmonic PWM. In terms of the modulation scheme above, the new configuration makes faster devices and high voltage devices operating in synergism possible. Comparison with four other single 5-level inverters is made in the paper. In order to verify the proposed approach experiment is developed. Output spectral analysis provides essential information for optimal design on whole inverter system. In general, computer simulation is responsible for the work. However, simulation results are susceptible to modulation parameters choice owing to switch waveforms error and DFT algorithm adopted. Considering simulation results accuracy modulation parameters have to be limited to certain extent. Thus simulation on spectral analysis is short in generality. Alternatively rigorous mathematical analysis on output spectra exactly overcomes the deficiency above. Based on the anatomy of hybrid modulation process in nature, 3-D mathematic models are built under three kinds of carrier dispositions frequently used. Further, by double FOURIER series expansion and intricate derivation, strict output analytic solution is acquired. The output analytical solution contains complete original information on output waveform spectra. Output spectral characteristics are summed up in the paper. Results from mathematical analytical solution are applicable not only to non overmodulation but also to overmodulation, and valid not only to synchronous modulation but also to asynchronous modulation. Further more, analytical solution educes an illuminative clue for spectral analysis on complicated output PWM waveforms based on different modulation strategies.更多还原