双电源非对称三电平逆变器及其调制策略的研究

发布时间：2018-12-09 16:34

【摘要】：逆变器是太阳能发电的重要构成部分,其主要作用是将太阳能电池中不稳定的直流电转变为三相交流电,从而实现并网发电,因此保证高质量的输出电压和输出频率,降低谐波将会是逆变器的主要研究方向。而逆变器中开关数目众多,结构复杂,因此也是太阳能发电系统中最容易损耗电能,造成发电效率低,成本投入大的部件。因此,对于逆变器的研究尤为重要。首先,论文介绍了光伏产业的现状以及现代逆变器的发展及研究现状,着重强调了研究多电平逆变器的重要性。多电平逆变器越来越受到工业和军方的关注。低电压可以通过级联的H桥、箝位式或者混合类型的多电平逆变器来驱使中高低的电平。由于多电平逆变器电平数量的增加,总的谐波失真也随之减小。多电平逆变器也对于保护环境起到了不可磨灭的作用。其次,论文对现有的三电平逆变器的拓扑结构和调制技术做了详细的阐述。现有的逆变器的结构主要包含二极管箝位式三电平逆变器和级联式多电平逆变器,分析了这几种逆变器的拓扑结构、工作原理及其优缺点。以NPC三电平逆变器为例,介绍了三角载波层叠法、三次谐波注入正弦PWM和次优调制、不连续PWM调制、上平顶波调制和下平顶波调制、对称平顶波调制、消除特定谐波法及空间矢量法的调制原理。然后,提出了一种新型的双电源非对称三电平逆变器拓扑结构,该结构的前级采用双电源双Buck降压变换器为后级逆变桥路提供四路电平,后级三相逆变桥包含四路开关桥臂。详细分析了前级双Buck变换器的工作原理以及后级三相逆变桥的四种工作状态。并将对称平顶波调制、1/4三次谐波注入、空间矢量调制应用到该非对称结构当中。分析了采用对称平顶波和1/4三次谐波注入调制时开关管的开关动作的产生机制,详细介绍了在NPC三电平逆变器基础上的空间矢量调制的每个步骤。并提出了一种新的调制策略-M相不动调制。最后,在Matlab/Simulink环境中进行仿真,分析了仿真结果,验证了双电源非对称三电平逆变器的可行性及调制策略的正确性。
[Abstract]:Inverter is an important component of solar power generation. Its main function is to convert the unstable direct current in solar cells into three-phase alternating current, so as to realize grid-connected power generation, so as to ensure high quality output voltage and output frequency. Harmonic reduction will be the main research direction of inverter. The inverter has a large number of switches and complex structure, so it is the most easy to lose electrical energy in the solar power system, resulting in low efficiency and large cost components. Therefore, the research of inverter is particularly important. Firstly, the status quo of photovoltaic industry and the development and research status of modern inverter are introduced, and the importance of studying multilevel inverter is emphasized. Multilevel inverter is attracting more and more attention from industry and military. Low voltage can be driven by cascaded H-bridge, clamped, or hybrid multilevel inverters. As the number of multilevel inverters increases, the total harmonic distortion decreases. Multilevel inverter also plays an indelible role in protecting the environment. Secondly, the topology and modulation technology of the three-level inverter are described in detail. The current structure of the inverter mainly includes diode clamped three-level inverter and cascaded multilevel inverter. The topology, working principle, advantages and disadvantages of these inverter are analyzed. Taking NPC three-level inverter as an example, the triangular carrier stacking method, third-harmonic injection sinusoidal PWM and sub-optimal modulation, discontinuous PWM modulation, upper flat-top wave modulation and lower flat-top wave modulation, symmetric flat-top wave modulation are introduced. The modulation principle of special harmonic method and space vector method is eliminated. Then, a novel topology of asymmetric three-level inverter with double power supply is proposed. The front stage of the structure uses dual power supply dual Buck step-down converter to provide four levels for the backstage inverter bridge, and the rear three-phase inverter bridge contains four switching arms. The working principle of the front-stage double Buck converter and the four working states of the rear-stage three-phase inverter bridge are analyzed in detail. The symmetric flat-top wave modulation, 1 / 4 third harmonic injection and space vector modulation are applied to the asymmetric structure. In this paper, the mechanism of switching operation of switching tube with symmetric flat-top wave and 1 / 4 third harmonic injection modulation is analyzed, and each step of space vector modulation based on NPC three-level inverter is introduced in detail. A new modulation strategy, M phase invariant modulation, is proposed. Finally, the simulation results in the Matlab/Simulink environment are analyzed, and the feasibility of the dual-power asymmetric three-level inverter and the correctness of the modulation strategy are verified.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM464

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