三电平NPC变换器中点电压波动抑制策略研究

发布时间：2018-01-28 12:19

本文关键词： 中点箝位型零序电压注入双调制波混合调制载波变幅调制　出处：《北京交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：三电平中点箝位型(Neutral-Point-Clamped,NPC)变换器具有结构简单,开关应力小,开关损耗少,电磁干扰低等优点,但其固有的中点电压不平衡的问题限制了这一拓扑在实际工业生产中的应用。本文主要针对三电平NPC变换器中点电压不平衡的问题进行研究。详细分析了三电平NPC变换器的工作原理,研究了变换器直流侧中点电压平衡机理。在此基础上,深入分析了零序电压和中点平均电流之间的关系,分三种情况讨论了零序电压的取值限制对中点平均电流的影响。零序电压注入法可以很好地控制三电平NPC变换器直流侧的中点平衡,具有原理简单、计算简便等优点,但是在调制系数较大或者功率因数较低的情况下存在不可消除的低频波动。双调制波法可以在全范围内消除中点波动,但会造成开关频率的增大和谐波性能恶化。针对零序电压法和双调制波法的优势和劣势,提出了零序电压注入和双调制波混合的调制方法,这种混合调制方法达到了在消除低频波动的同时又能最大程度上降低开关频率和保持谐波性能的目的。深入研究了载波变幅调制对三电平NPC变换器输出参考电压的影响,得出了载波幅值随着直流侧上下电容电压成比例变化时三电平NPC变换器能够输出理想基波幅值的参考电压和保持输出参考电压伏秒平衡的结论。在此基础上,提出了基于载波变幅求解零序电压的中点电压平衡控制方法。该方法首先将载波幅值按照直流侧上下电容电压成比例变化,保持输出参考电压相关特性,然后根据控制直流侧中点电压平衡的原理向三相参考电压中注入合适的零序电压,控制直流侧中点电压平衡。这种控制策略不仅能够使直流侧中点电压达到平衡,而且还能保持输出参考电压的相关特性。搭建了三电平NPC变换器实验平台,并对本文所提出的控制策略进行了实验。实验结果证明了本文所提出的中点电压平衡控制策略的正确性和有效性。
[Abstract]:Three-level Neutral-Point-Clampedn NPC (NPC) converter has the advantages of simple structure, low switching stress, low switching loss and low electromagnetic interference. However, the inherent neutral point voltage imbalance has limited the application of this topology in practical industrial production. In this paper, the unbalanced neutral point voltage of three-level NPC converter is studied in detail. The principle of level NPC converter. The mechanism of neutral voltage balance in DC side is studied, and the relationship between zero-sequence voltage and midpoint average current is analyzed. The effect of zero sequence voltage limit on the average neutral current is discussed in three cases. The zero sequence voltage injection method can well control the neutral point balance in the DC side of the three-level NPC converter, and the principle is simple. It is easy to calculate, but there are some low frequency waves in the case of high modulation coefficient or low power factor. The double modulation wave method can eliminate the midpoint fluctuation in the whole range. However, the switching frequency will increase and the harmonic performance will deteriorate. Aiming at the advantages and disadvantages of zero-sequence voltage method and dual-modulation wave method, a hybrid modulation method of zero-sequence voltage injection and dual-modulation wave is proposed. The hybrid modulation method can reduce the switching frequency and maintain the harmonic performance at the same time as eliminating the low frequency fluctuation. The output reference of the three-level NPC converter based on the carrier variable amplitude modulation is deeply studied. The effect of voltage. It is concluded that the three-level NPC converter can output the reference voltage of the ideal fundamental amplitude and keep the balance of the output reference voltage in volts when the carrier amplitude varies proportionally with the voltage of the DC side up and down. On this basis, the conclusion is drawn that the three-level NPC converter can output the reference voltage of the ideal fundamental amplitude. . A midpoint voltage balance control method based on carrier amplitude-varying solution to zero sequence voltage is proposed. Firstly, the carrier amplitude is proportional to the upper and lower capacitance voltage of the DC side to maintain the output reference voltage-related characteristics. Then according to the principle of controlling the midpoint voltage balance at the DC side, a suitable zero-sequence voltage is injected into the three-phase reference voltage. This control strategy can not only balance the neutral voltage of DC side, but also maintain the characteristics of output reference voltage. A three-level NPC converter experimental platform is built. The experimental results show that the proposed midpoint voltage balance control strategy is correct and effective.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM46

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