新型多电平高效逆变器及其调制方法研究

发布时间：2018-12-27 10:37

【摘要】：由前级升压器和后级逆变电路构成的两级结构的逆变器具有一些优点:它能适应较低的或大范围变化的直流侧电压,工作于较高的稳定电压的后级逆变电路的效率较高、成本较低且易于控制。但是现有的基于boost结构的前级升压器带来的功率损失和成本增加会抵消这些优点,以至于两级结构的逆变器不具有优势,选用两级结构的逆变器多是被动选择。为降低两级逆变器的功率损耗,提高两级逆变器的实用价值,文章从三个方面予以改进:(1)改变拓扑结构。提出了一种两级式三相逆变器,该拓扑结构前级利用两个互补的buck变换器,能够为后级提供四路输出电平,并且一部分电能直接从电源供电,不经过前级,可以大大减小前级的电流。通过Matlab/Simulink仿真,计算出前级双buck结构比普通boost结构的前级开关损耗降低了86%以上。后级采用非对称三电平结构,能够利用前级电路的特点来减小后级开关损耗。(2)改变调制方法。针对互补buck型两级逆变器结构的特点,提出了依托中间电平调制法。分别从前级开关损耗、后级逆变器开关损耗、磁损耗等方面详细比较了依托中间电平调制法与三次谐波注入法、对称平顶波调制法以及不注入零序分量的正弦波调制法各自的优缺点,研究结果证明了依托中间电平调制法能够全方位降低逆变器的损耗,是该逆变器最理想的调制方法。(3)软开关技术。使用了一种ZVS PWM软开关实现策略,应用于所提出的具有两个buck结构的两级逆变器的前级,能够使前级的所有开关管实现软关断。通过仿真和实验验证了该方案的正确性和可行性。
[Abstract]:The two-stage inverter, which is composed of the front stage booster and the back stage inverter, has some advantages: it can adapt to the low or wide range of DC side voltage, and it is more efficient to work in the back stage inverter circuit with higher stable voltage. Low cost and easy to control. However, the power loss and cost increase brought by the existing front-stage booster based on boost structure will offset these advantages, so the two-stage inverter has no advantage, and the two-stage inverter is mostly passive. In order to reduce the power loss of the two-stage inverter and improve the practical value of the two-stage inverter, this paper improves it from three aspects: (1) changing the topology. In this paper, a two-stage three-phase inverter is proposed. The topology structure uses two complementary buck converters to provide four output levels for the rear stage, and a portion of the electric energy is supplied directly from the power supply without passing through the front stage. The current in the front stage can be greatly reduced. By Matlab/Simulink simulation, it is calculated that the switching loss of the front double buck structure is more than 86% lower than that of the common boost structure. The rear stage adopts an asymmetric three-level structure, which can reduce the switching loss of the back stage by utilizing the characteristics of the front stage circuit. (2) the modulation method is changed. According to the characteristics of complementary buck two-stage inverter, an intermediate level modulation method is proposed. This paper compares the intermediate level modulation method with the third harmonic injection method in detail from the aspects of the front stage switching loss, the back stage inverter switching loss, the magnetic loss and so on. The advantages and disadvantages of symmetric flat-top wave modulation method and sine wave modulation method without zero sequence component are discussed. The results show that the intermediate level modulation method can reduce the loss of inverter in all directions. It is the most ideal modulation method for the inverter. (3) soft switching technology. In this paper, a ZVS PWM soft switch implementation strategy is applied to the front stage of the two-stage inverter with two buck structures, which can make all the former switches soft off. The correctness and feasibility of the scheme are verified by simulation and experiment.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464

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