【作者】 龚博；

【导师】 秦忆； 程善美；

【作者基本信息】 华中科技大学 ， 控制理论与控制工程， 2013， 博士

【摘要】 三电平变换器的出现,为高压大功率系统的实现提供了同时兼顾大容量和高性能的解决方案。因此三电平技术已经成为电力电子技术中一个非常活跃的研究方向。在三电平结构中,二极管箝位型三电平逆变器以其结构简单、成本较低等优点得到广泛的研究和应用。本文对二极管箝位型三电平逆变器的正弦脉宽调制策略进行了深入研究,同时建立平均中点电流模型,对二极管箝位型三电平逆变器中点电压的波动进行了分析。本文讨论了三电平逆变器中点电压波动产生的原因,为系统直流滤波电容的设计和中点电压控制提供了理论依据和指导。在此基础上,本文分别从载波和调制波的角度,研究不同调节量对中点电压的影响。本文以中点电流为基础深入分析了载波幅值对中点电压的影响作用,具体推导出中点电压与载波幅移的数学表达式,从而在此基础上提出了基于载波幅移的中点电压的控制方法。将载波幅值的改变等效到改变调制波上可以得到同样的中点电压波动抑制效果,为了简化计算,便于实现,又提出了中点电压控制的调制波方法,该方法也为三电平载波与调制波相互转换提供了新思路。本文研究了载波交叠与中点电压的关系,分析了改变载波垂直位置的载波交叠方法对中点电压的影响作用,从而在此基础上得到了基于载波交叠的中点电压控制方法,为了防止在线性调制区出现过调制对系统输出造成不利影响,提出了基于载波交叠和载波幅移的混合载波交叠方法,该方法可以通过只改变一组载波的幅值来实现对中点电压波动的抑制。在充分研究载波交叠量的基础上,提出了基于载波交叠的SPWM调制策略。该调制策略使交叠区间对称地分布在横轴两侧,中点电压不会发生偏移,但是可以有效地提高系统(尤其是在调制比较低时)的输出波形质量。调制波改变主要有两种形式,一种是叠加直流分量,一种是叠加谐波分量,本文分析了调制波改变对中点电压的影响。本文证明了叠加直流分量可以使中点电压发生偏移,同时给出了三电平SPWM方法与SVPWM方法区间的映射关系。因此叠加直流偏移量的方法也可以引入到三电平SVPWM方法中,在此基础上提出了基于叠加直流偏移量的中点电压波动的抑制方法。本文进一步分析了叠加谐波分量对中点电压的影响,当注入的是六倍次谐波时,中点电压会发生偏移,偏移的方向可以用注入谐波的相位来控制,并且给出了中点电压偏移与注入的谐波幅值的具体关系。在此基础上提出了基于六次谐波注入的闭环中点电压控制方法。为了对以上理论研究进行验证,搭建了基于DSP+CPLD双核结构的三电平逆变器实验平台。在实验平台上对本文所提出的三电平中点电压的波动特性以及基于载波和基于调制波的中点电压控制策略等进行了实验研究。仿真和实验结果验证了本文理论研究工作的正确性。更多还原

【Abstract】 The emergence of three-level converter provides the solutions for the realization of high-voltage high-power system with large-capacity and high-performance, therefore, the three-level technology has become a very active area in power electronics technology. As the advantages of simple structure and low cost, the diode clamped three-level inverter has been widely studied and applied.Sinusoidal pulse width modulation strategy for diode clamped three-level inverter is detailedly studied in this dissertation. And the neutral point current model is established, the variation and offset of neutral point voltage are analyzed. The causes of neutral point voltage fluctuation are discussed, and the research provides a theoretical basis and guid-ance for the filter capacitors design and the neutral point voltage control. Based on the analysis, the impacts of different adjustments on neutral point voltage are studied from the angle of the carrier wave and modulated wave, respectively.The impact of the carrier’s amplitude on the neutral point voltage based on neutral point current, and derives the mathematical expression between neutral point voltage and scale of the carrier’s amplitude is studied in this dissertation. With the relationship between neutral point voltage and carrier’s amplitude, a neutral point voltage control scheme based on carrier amplitude scaling is proposed. The same effect can also be achieved by an equivalent transformation of the carrier amplitude scaling to modulation wave. In order to simplify the calculation, facilitate the realization, the modulation wave control mode for neutral point voltage control is proposed. It also explores new ideas of the conversion be-tween carriers and modulation wave in three-level systems. The relationship between neu-tral point voltage and carrier overlap is studied in this dissertation. With analyzing the im-pact of the carrier overlap method based on changing the vertical position of the carriers on the neutral point voltage, the neutral point voltage control scheme based on carrier overlap is proposed. In order to avoid the adverse effects of the over modulation in linear modulation area, a hybrid carrier overlap method based on carrier amplitude scaling is proposed, the neutral point voltage control can be achieved by changing only one carrier’s amplitude. In the full study of the carrier’s overlap, a SPWM modulation strategy based on the carrier overlapping is proposed. The overlap displays a symmetrical distribution on the horizontal axis for the strategy, it does not make the neutral point voltage offset, but can effectively improve the output waveform quality (particularly in the low modulation area).There are two main forms of modulation wave changes, one is by adding DC offset, and the other is by adding harmonic components. The impact of the changed modulation wave on the neutral point voltage is analyzed. The DC offset can make the neutral point voltage shift is proved, and the range mapping relationship between SPWM and SVPWM for three-level systems is given, in this dissertation. Therefore, adding DC offset can also be introduced into the three-level SVPWM method. And the neutral point voltage control scheme by adding DC offset is proposed. The relationship between adding harmonic com-ponents and neutral point voltage is further analyzed, it shows that the neutral point volt-age will shift by adding6n times harmonic components, the direction of shift is deter-mined by the phase of injected harmonic components. The specific relationship between neutral point voltage and injected harmonic amplitude is given. With the relationship, the closed-loop neutral point voltage control method by injecting sixth-order harmonics is proposed.In order to validate the above theoretical studies,a three-level inverter is built based on the DSP+CPLD platform. All proposed strategies and analysis, three-level neutral point voltage fluctuation characteristics, the proposed neutral point voltage control strategy based on carriers and modulation wave, are studied on the experimental platform. Simula-tion and experimental results fully verify the correctness of theoretical research in this dis-sertation.更多还原