模块化多电平变流器综合控制策略研究

发布时间：2018-07-09 15:37

本文选题：模块化多电平变流器 + 充电控制　；参考：《哈尔滨工业大学》2014年硕士论文

【摘要】：随着电力电子技术向着高压、大功率变换方向的不断发展，尤其是电压源型变流器在柔性直流输电系统中的广泛应用，针对大功率变流器的研究越发重要。然而，传统两电平及多电平变流器在高压领域应用时控制复杂，扩展性差，成为了其发展的制约瓶颈。模块化多电平变流器(Modular Multilevel Converter,MMC)因其具有模块化结构，在传统变流器优势的基础上，增加了向不同电压等级的扩展性，更加适用于输电领域。本文首先对MMC拓扑结构，运行原理，数学模型，及PWM调制策略进行了分析，基于以上分析对内部环流成分及模块电容容量的计算进行了研究。其次，针对MMC启动时模块电容电压的建立进行了研究，提出了从交流侧为电容恒流充电的方法，将上、下桥臂各视为两并联于同一电网的变流器，进行解耦控制，为模块电容恒流充电。本文提出的充电方法，不仅避免了过流冲击现象，而且同一桥臂电容同时充电，充电快速，一致性好。再次，针对模块电容电压平衡及环流控制问题，分析了现有控制方法，从能量角度推导出了上、下桥臂之间平衡控制的最快途径。本文提出相间电容电压平衡结合环流抑制，相内桥臂间与桥臂内平衡的三级控制策略，通过相间电压平衡结合环流控制，实现相间电压均衡，并将环流控制为直流量，消除环流谐波的目的，相内通过桥臂之间与桥臂内的平衡控制，平衡了相内电容电压。然后，针对基于MMC换流站的输电系统的控制，分析了功率控制原理，利用前馈解耦控制达到对有功和无功功率分量的独立控制目标。在此基础上，对MMC互联交流电网异常工况下给出应对措施，分别对具有高阻抗电网和电网电压不平衡情况时，得出换流站控制方式，使MMC换流站能够带故障安全运行。最后，，本文设计搭建了MMC实验样机平台，通过Matlab仿真对提出方法研究，并在实验装置上进行验证。结果均表明提出方法的正确性和有效性。
[Abstract]:With the development of power electronics technology towards high voltage and high power conversion, especially the wide application of voltage source converter in flexible DC transmission system, the research of high power converter becomes more and more important. However, the traditional two-level and multilevel converters have complex control and poor expansibility when they are applied in the high voltage field, which has become the bottleneck of their development. Modular multilevel converters MMC (Modular multilevel Converters MMC) is more suitable for transmission because of its modularized structure and the advantages of traditional converters which increase the expansibility to different voltage levels. In this paper, the topology, operation principle, mathematical model and PWM modulation strategy of MMC are analyzed. Based on the above analysis, the calculation of the internal circulation composition and the capacitance capacity of the module is studied. Secondly, the establishment of module capacitor voltage during MMC start-up is studied, and the method of charging capacitor constant current from AC side is put forward. The upper and lower arms are regarded as two converters parallel to the same power grid, and decoupling control is carried out. Constant current charge for module capacitance. The charging method proposed in this paper not only avoids the phenomenon of overcurrent shock, but also charges simultaneously with the same bridge arm capacitance, which makes the charging fast and consistent. Thirdly, aiming at the problems of capacitor voltage balance and circulation control of modules, the existing control methods are analyzed, and the fastest way to balance control between upper and lower arms is deduced from the angle of energy. In this paper, a three-stage control strategy of capacitor voltage balance and interphase voltage balance is proposed to realize the voltage balance between two phases, and the circulation is controlled as a direct flow rate by combining the voltage balance between the phases with the current suppression, and the balance between the two arms of the phase and the inside of the bridge arm. The purpose of eliminating the circulation harmonics is to balance the capacitance voltage between the two arms. Then, the principle of power control is analyzed for the control of transmission system based on MMC converter station. The feedforward decoupling control is used to achieve the independent control goal for active and reactive power components. On this basis, the countermeasures are given for MMC interconnected AC power grid under abnormal working conditions. When there are high impedance power grid and voltage imbalance, the control mode of converter station is obtained, so that MMC converter station can operate safely with fault. Finally, the MMC experimental prototype platform is designed and built, and the proposed method is studied by Matlab simulation, and verified on the experimental device. The results show that the proposed method is correct and effective.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM46

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