基于三电平三相逆变器的调制策略研究

【作者】 李政学；

【导师】 李正熙； 陈亚爱；

【作者基本信息】 北方工业大学 ， 检测技术与自动化装置， 2007， 硕士

【摘要】 近年来，新型三电平逆变器由于具有输出容量大、输出电压高、电流谐波含量小的优点，在中高压调速领域、交流柔性供电系统的无功补偿中得到了广泛的应用。本文主要对三电平逆变器的拓扑结构及调制策略进行了深入研究，论述和分析了三电平变换技术的关键性问题，并得出了相应结论。本文首先对中高压三电平逆变器的发展现状做了较为详细的综述，以中点箝位三电平逆变器的基本拓扑结构为基础，着重分析了三电平空间电压矢量调制基本原理，提出了一种采用最近三矢量法合成参考矢量的空间矢量脉宽调制算法，给出了小三角形区域判断规则、合成参考电压矢量的相应输出电压矢量作用顺序和开关信号的产生方法，探讨了影响三电平逆变器中点电压平衡的主要因素，并推导出各合成电压矢量的作用时间。有三种主要的中点电位控制方法：①、消极“控制”：在一系列开关周期中交替使用正负小矢量，这种方式只有在负载平衡情况很好的情况下使用，而且这种方法的鲁棒性很差。②、滞环控制：是最简单也是最流行的闭环中点电位控制策略，使用这种方法需要知道每相的电流方向，能使中点电位趋势平衡的小矢量将被选择。该方法的缺点是仍将产生中点电位波动。③、控制m_s0和m_s1使中点电位精确平衡，这种方法需要测量相电流的大小和方向。优点是能抑制中点波动，缺点是由于引入额外的开关状态而增加开关损耗，而且鲁棒性也不如滞环控制方法。在三电平逆变器空间矢量调制策略的数字化实现中，给出了控制系统的总体设计方案，分别设计了系统的硬件结构和部分软件流程，硬件部分主要包括双DSP及CPLD的设计，软件部分包括各部分程序及软件仿真，在对软件仿真结果详细分析的基础上，对实验结果进行了分析，比较和研究。实验和仿真结果都证明了本文提出的空间矢量调制策略及三电平逆变器拓扑结构的可行性及优越性。更多还原

【Abstract】 Three-level inverters have been becoming increasingly popular in recent years in medium-high voltage ac drive systems and FACTS equipments, mainly due to their high voltage-capability, high output quality, low switching losses and low EMC concerns. The paper primarily makes an in-depth research on the multilevel inverter topological structure and modulation strategy, and then the key problems concerning multilevel converter technique are described and analyzed. Firstly, the development of medium-voltage three-level inverter is introduced ; based on the basic topology of three-level neutral-point-clamped inverter, the basic principle of Space Vector Pulse Width Modulation for three-level inverter is described. A novel Space Vector Modulation algorithm is proposed by using the nearest three vectors as reference voltage vector. The judging rules of the small sectors and the out voltage vector sequence are presented as well as the producing of the signals for SVPWM. The main factors for the neutral-point imbalance are discussed . Also, the dwelling time of each vector is computed. The analysis of other sectors is realized by transforming the sectors.Passive "control" , where the positive and negative small vector is selected alternatively in each new switching cycle. This method can work only in the case of perfectly balanced load and perfectly balanced PWM scheme, which is unlikely to happen in practice. This method would have difficulties to recover from line or load transients. Still, this "control" method can be used to establish a benchmark for NP controller performance. This benchmark can then be used to evaluate the performance of other NP control methods. Hysteresis type control is perhaps the simplest and most popular closed loop NP control scheme. This method requires the knowledge of the current direction in each phase. Based on that information, the small vectors that will move the NP voltage in the direction opposite from the direction of unbalance can be selected. The downside of this method is the current ripple at half the switching frequency. Active control schemes that control the current modulation indexesm_s0 and m_s1. Ingeneral, these schemes require measurement of the voltage unbalance in the NP, and often require measurement of the amplitudes of the phase currents as well. The benefits of these schemes is that they do not have the ripple at half the switching frequency, and some variations of these control schemes can balance the NP exactly. Unfortunately, they all increase the switching losses due to introduction of additional switching states, and may be less robust than the hysteresis type control schemes.In the digital realization of SVPWM modulation in three-level inverter, the design scheme of control system is provided, system hardware structure and software flowchart is designed separately, mainly includes the design of double DSP and CPLD. The realization manner of SVPWM is analyzed in detail, program and experimental results are analyzed and compared. The feasibility and superiority of SVPWM in three-level inverters are proved.更多还原