多电平逆变器空间矢量调制策略及电容电压平衡研究

发布时间：2018-03-26 00:38

本文选题：多电平　切入点：逆变器　出处：《兰州理工大学》2014年硕士论文

【摘要】：多电平逆变器以其高性能和大容量方面的突出优势已成为人们研究与应用的热点之一。在多电平逆变器的多种控制策略中,空间矢量脉宽调制(SVPWM)算法具有调制比大、能够优化输出电压波形等优点,通过对SVPWM算法改进可以改善控制性能。三电平NPC逆变器以其结构简单、成本较低等优点得到了广泛的研究和应用,但电容电压平衡是影响其安全运行和输出性能的关键问题之一,对该问题的研究具有重要的理论和工程价值。论文以三电平NPC逆变器为例对不同坐标系下多电平SVPWM调制方法进行了研究。为解决计算复杂的问题,根据基本矢量在α'β'两相坐标平面的坐标都是整数的规律,研究得到一种在α'β\侈坐标系下多电平SVPWM的通解,实现多电平SVPWM算法的统一简化。利用得到的多电平SVPWM通解,提出了一种电路中各个开关器件的开关次数最少的调制方案,即每次只有一相输出电压改变,且只改变一个电平单位的切换。为了寻求合适的切换路径以降低开关次数,在α'β'平面上,提出了特征网络和特征四边形的概念,利用扇区序列S的每个顶点去逼近参考电压矢量ur。。研究表明参考电压轨迹的半径所在的范围不同,特征网络具有两种不同的形状。在这两种特征网络中,以特征四边形为基础分析了总开关切换次数最小的切换路径,提出了优化开关频率的SVPWM算法。仿真结果表明,该算法在一个参考电压周期内的总开关切换次数与相同参数下同相层叠正弦调制算法相比降低了25%。针对NPC型逆变器存在的电容电压波动问题,提出一种小矢量在线自调节的方法,此方法可以实现NPC电容电压在各个工况点的有效控制。论文从矢量和中点电流的影响角度深入分析了中点电位平衡控制的规律,通过设计平衡系数,动态调节不同小矢量的作用时间,以此实现对电容电压的控制。仿真实验及结果验证了分析结论和控制方法的正确性。最后,设计了三电平NPC逆变器及实验方案,进行了硬件和软件设计,并进行仿真研究。
[Abstract]:Multilevel inverter has become one of the hotspots in research and application because of its outstanding advantages in high performance and large capacity. In many control strategies of multilevel inverter, space vector pulse width modulation (SVPWM) algorithm has a large modulation ratio. The output voltage waveform can be optimized and the control performance can be improved by improving the SVPWM algorithm. The three-level NPC inverter has been widely studied and applied because of its simple structure and low cost. However, capacitor voltage balance is one of the key problems affecting its safe operation and output performance. The study of this problem has important theoretical and engineering value. In this paper, a three-level NPC inverter is taken as an example to study the multilevel SVPWM modulation method in different coordinate systems. In order to solve the complex problem of calculation, according to the law that the coordinates of the basic vectors in the 伪'尾 'two-phase coordinate plane are integer. In this paper, a general solution of multilevel SVPWM in 伪'尾\ luxury coordinate system is obtained, and the unified simplification of multilevel SVPWM algorithm is realized. Using the obtained general solution of multilevel SVPWM, a modulation scheme with minimum switching times for each switch device in the circuit is proposed. That is, only one phase output voltage changes, and only one level unit switching. In order to find a suitable switching path to reduce the number of switches, the concepts of characteristic network and characteristic quadrilateral are proposed on the 伪'尾 'plane. Using each vertex of sector sequence S to approach the reference voltage vector ur.The study shows that the radius of the reference voltage locus is different, and the characteristic network has two different shapes. Based on the characteristic quadrilateral, the switching path with minimum switching times is analyzed, and the SVPWM algorithm is proposed to optimize the switching frequency. The simulation results show that, Compared with the in-phase stacked sinusoidal modulation algorithm with the same parameters, the total switching times of the algorithm in a reference voltage cycle are reduced by 25%. Aiming at the problem of capacitor voltage fluctuation in NPC inverter, a method of on-line self-adjusting with small vector is proposed. This method can realize the effective control of NPC capacitor voltage at each working point. The law of midpoint potential balance control is deeply analyzed from the angle of vector and midpoint current, and the balance coefficient is designed. The effect time of different small vectors is dynamically adjusted to realize the control of capacitor voltage. The simulation experiment and result verify the correctness of the analysis conclusion and the control method. Finally, the three-level NPC inverter and its experimental scheme are designed, and the hardware and software are designed and simulated.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464

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