多电平变流器SVPWM简化算法研究

发布时间：2018-06-22 02:45

本文选题：二极管钳位式多电平变流器 + 五电平NPC/H桥变流器　；参考：《中国矿业大学》2014年硕士论文

【摘要】：多电平变流器具有减小输出电流、电压谐波及降低开关器件应力的优点，其应用越来越广泛，脉宽调制算法是决定变流器输出特性的关键因素之一。本论文分别以三相三线制二极管钳位式多电平变流器、级联式多电平变流器为研究对象，对其调制方法进行详细分析和研究，给出易于实现的简化调制策略。针对三相三线制二极管钳位式多电平变流器，传统空间矢量脉宽调制策略(SVPWM)扇区判断繁琐，作用时间计算复杂，本文提出二极管钳位式三电平变流器简化SVPWM算法，该算法的思路：基于分类算法推导各桥臂开关的开关时刻，归纳其特点，给出算法实现的简化方法。算法在实现过程中无需扇区判断等中间步骤，可直接根据参考电压得出各开关的开关时刻。对三电平简化SVPWM算法进行仿真和实验验证，结果表明所提出的简化调制策略能够较准确的等效参考电压。将简化算法推广到五电平，与基于非正交60g h坐标系空间矢量脉宽调制算法比较，简化算法的运行速度及效果均优于后者。控制中点电位平衡是制约三电平NPC（Neutral-Point Clamped）拓扑结构推广和应用的一大难题。本文在分析各矢量对变流器中点电位影响效果的基础上，采用控制中点电荷的方案调节直流侧中点电位，理论分析可知通过控制正负小矢量的作用时间能够抵消直流侧中点电荷，使中点电位达到动态平衡。结合三电平简化SVPWM调制策略，推导中点电位简化控制策略，仿真结果表明采用的调制策略能够控制中点电位在允许范围内。考虑死区效应，分析在不同电流极性情况下，变流器理想输出电压与开关状态的关系，在此基础上给出死区优化补偿策略，仿真验证了该死区补偿策略的有效性。五电平NPC/H桥变流器相比于钳位式多电平变流器，钳位二极管少，不存在均压问题，论文研究该拓扑的换流方式，建立多电平变流器的数学模型，以此为理论基础，分析其调制策略。对比钳位式五电平NPC拓扑，根据变流器输出电平与开关状态的对应关系，在分析和确定五电平NPC/H桥各开关器件编号的前提下，应用五电平简化SVPWM实现其调制；结合载波相移(SPWM)与三电平简化SVPWM算法，令两个三角载波相位相差π/2，，将五电平NPC/H桥变流器的调制转化为三电平变流器的调制。仿真验证两种调制方法均能实现五电平NPC/H桥变流器的调制，且载波相移调制策略的运行速度与仿真效果优于五电平简化SVPWM控制方法，实验验证了载波相移与三电平简化SVPWM相结合调制策略的有效性。
[Abstract]:Multilevel converter has the advantages of reducing the output current, voltage harmonics and reducing the stress of switching devices. The pulse width modulation algorithm is one of the key factors to determine the output characteristics of the converter. In this paper, three-phase three-wire diode clamped multilevel converters and cascaded multilevel converters are taken as the research objects. The modulation methods are analyzed and studied in detail, and a simplified modulation strategy is given. Aiming at three-phase three-wire diode clamped multilevel converter, the traditional space vector pulse width modulation (SVPWM) sector judgment is tedious and the calculation of operation time is complicated. In this paper, a simplified SVPWM algorithm for diode clamped three-level converter is proposed. The idea of this algorithm: based on the classification algorithm, the switching time of each arm switch is deduced, the characteristics of the switch are summarized, and the simplified method of the algorithm implementation is given. In the process of implementation, the switching time of each switch can be obtained directly from the reference voltage without the intermediate steps such as sector judgment. The simulation and experimental results of the three-level simplified SVPWM algorithm show that the proposed simplified modulation strategy can provide an accurate equivalent reference voltage. The simplified algorithm is extended to five levels. Compared with the space vector pulse width modulation algorithm based on non-orthogonal 60g h coordinate system, the speed and effect of the simplified algorithm are better than that of the latter. Controlling neutral-point potential balance is a difficult problem that restricts the promotion and application of three-level NPC (Neutral-Point Clamped) topology. Based on the analysis of the effect of each vector on the midpoint potential of the converter, the midpoint potential at the DC side is regulated by the scheme of controlling the mid-point charge. Theoretical analysis shows that the midpoint charge can be offset by controlling the action time of positive and negative small vectors, and the midpoint potential can reach dynamic equilibrium. Combined with the three-level simplified SVPWM modulation strategy, the simplified neutral point potential control strategy is derived. The simulation results show that the proposed modulation strategy can control the neutral point potential within the allowable range. Considering the dead-time effect, the relationship between the ideal output voltage and the switching state of the converter under different current polarity is analyzed. On the basis of this, the dead-time optimal compensation strategy is given, and the effectiveness of the damned zone compensation strategy is verified by simulation. Compared with the clamped multilevel converter, the five-level NPC-H bridge converter has fewer clamping diodes and no voltage-sharing problem. This paper studies the converter mode of the topology and establishes the mathematical model of the multilevel converter, which is the theoretical basis. The modulation strategy is analyzed. Compared with the clamped five-level NPC topology, according to the corresponding relationship between the output level of the converter and the switching state, and under the premise of analyzing and determining the switching device numbers of the five-level NPC-H bridge, the five-level simplified SVPWM is used to realize the modulation. Combining the carrier phase shift (SPWM) algorithm with the three-level simplified SVPWM algorithm, the phase difference between the two triangular carriers is 蟺 / 2. The modulation of the five-level NPC-H bridge converter is converted into the modulation of the three-level converter. The simulation results show that both of the two modulation methods can realize the modulation of five-level NPC-H bridge converter, and the speed and simulation result of the carrier phase-shift modulation strategy are better than that of the five-level simplified SVPWM control method. The effectiveness of the modulation strategy combined with carrier phase shift and three-level simplified SVPWM is verified by experiments.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM46

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