三电平逆变器断续混合调制与中点平衡控制研究

发布时间：2018-05-05 07:04

本文选题：二极管箝位式拓扑结构 + 三电平逆变器　；参考：《沈阳工业大学》2017年硕士论文

【摘要】：光伏中点箝位型并网逆变器的原理是利用太阳能电池板储存的直流电能转化为可以直接并网使用的交流电,对其性能的有严格的要求。本文深入分析了NPC型三电平并网逆变器,着重解决其存在于调制方法的和中点电位波动中的两个问题。首先,本文前期参阅了许多的国内外有关书籍资料,综述了光伏发电的背景和意义,国内外的研究现状以及光伏系统的分类,详细阐述了NPC型逆变器的调制策略和中点波动问题的研究现状。其次,重点分析了逆变器的几种重要的拓扑结构,对结构不同的逆变器的特点进行了比较分析,并且总结出逆变器的数学模型。为了达到降低开关损耗同时保证低的谐波畸变和输出电压的质量的目的,深入分析了七段式调制和五段式调制各自的特点以及不足,七段式调制的优点是能够保证输出电压稳定,五段式的特点为可以降低开关频率。结合两者的优点,根据五段式断续调制策略开关停滞区间为120°,按照开关动作次数更少,且每次开关动作时只允许一个桥臂动作,推导出断续混合调制策略,即一个基波周期内的相邻30°扇区采用不同的调制方法,并且通过计算将两电平作用时间修正为三电平,简化了计算过程,归纳出断续混合调制策略的实现方法。最后,针对二极管箝位式拓扑结构的固有中点电位波动问题,在断续混合调制策略的方法下提出了一套中点电位控制方案,将两电容的差值不断与标准值进行比较,通过判断差值的大小,以反比例调整正负半周断续脉宽的宽度,改变小矢量的作用时间。如果正半周箝位的部分延长,其保持高电平状态的时间也相应的延长,因此高电平状态下的小矢量作用时间增加。同时负半周箝位的部分缩短,低电平状态小矢量作用时间缩短。正负半周断续部分的反比例调整,保证了一个周期内箝位角度是固定的,避免了断续部分与其他相的重叠。
[Abstract]:The principle of grid-connected photovoltaic inverter is to convert the stored DC energy from solar panels to AC which can be directly connected to the grid, which has strict requirements for its performance. In this paper, NPC three-level grid-connected inverter is deeply analyzed, and two problems existing in modulation method and neutral point potential fluctuation are emphatically solved. First of all, this paper reviewed many domestic and foreign books, summarized the background and significance of photovoltaic power generation, domestic and foreign research status and photovoltaic system classification. The modulation strategy and midpoint fluctuation of NPC inverter are described in detail. Secondly, several important topology structures of the inverter are analyzed, the characteristics of the inverter with different structure are compared and analyzed, and the mathematical model of the inverter is summarized. In order to reduce switching loss and ensure the quality of harmonic distortion and output voltage, the characteristics and shortcomings of seven-segment modulation and five-segment modulation are analyzed. The advantage of seven-segment modulation is that the output voltage is stable and the five-segment modulation can reduce the switching frequency. Combining the advantages of the two methods, according to the five-segment intermittent modulation strategy, the switching stagnation range is 120 掳, according to the number of switching actions is less, and only one bridge arm is allowed for each switching operation, the intermittent mixed modulation strategy is deduced. In other words, different modulation methods are used in the adjacent 30 掳sector of a fundamental wave period, and the two-level action time is corrected to three-level by calculation, which simplifies the calculation process and induces the realization method of intermittent mixed modulation strategy. Finally, aiming at the inherent midpoint potential fluctuation of diode clamped topology, a set of midpoint potential control scheme is proposed under intermittent mixed modulation strategy. The difference between the two capacitors is constantly compared with the standard value. By judging the magnitude of the difference, the width of positive and negative half-cycle intermittent pulse width is adjusted in inverse proportion, and the action time of small vector is changed. If the partial length of the positive half-cycle clamping is extended, the time of holding the high level state is also prolonged accordingly, so the time of small vector action in the high level state is increased. At the same time, the negative half cycle clamping part is shortened, and the low level state small vector operation time is shortened. The inversely proportional adjustment of the positive and negative half-cycle intermittent parts ensures that the clamping angle is fixed in a period and avoids the overlap between the intermittent parts and other parts.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464

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