模块化多电平功率变换系统基础研究

发布时间：2018-08-30 19:43

【摘要】：近年来电力电子变换器技术得到了飞速发展，高压大功率能量转换系统的需求也日益增长。多电平变换器通过改进变换器自身拓扑结构来突破功率半导体器件容量的限制，已成为高压大功率电能变换应用领域中的一种理想的解决方案。模块化多电平变换器(Modular Multilevel Converter, MMC)以其突出的技术特点，克服了传统多电平变换器的缺陷，是目前高压大功率电力系统中最有吸引力的多电平变换器拓扑结构。为此，本文围绕模块化多电平功率变换系统的电压平衡方法、调制技术、容错控制策略以及在光伏发电领域的应用进行了深入细致的研究。具体内容包括以下几个方面：论文首先分析了MMC的子模块电容电压平衡问题。从MMC运行机制出发，建立MMC广义动态模型，分析和比较了两种传统子模块电容电压平衡方法，然后在此基础上提出一种基于归并网络的预测排序算法，分别从提高排序算法的效率和限制排序算法的工作频率两方面进行了改进，使子模块电压平衡控制方法对硬件的依赖程度降低，能够减轻控制器负担，降低变换器的开关频率。论文对MMC的阶梯波调制和标量脉宽调制的两种调制技术进行了深入的研究。首先研究了适用于MMC的阶梯波调制技术，针对牛顿迭代法在求解阶梯波调制的MMC开关角时的局部收敛性问题，提出一种改进的混合粒子群优化算法，在求解的开始阶段采用粒子群优化算法全局范围内随机搜索开关角方程的迭代初值，之后运用牛顿法快速迭代到精确解。其次，针对MMC矢量调制标量化问题，提出一种具有电容电压平衡能力的标量脉宽调制方法，在一维矢量空间上以最近的两个电平线性地合成期望输出电压，合成矢量的作用时间只需要简单的占空比计算即可实现，可以省去繁琐的三角函数运算和坐标变换。论文对上述两种调制技术进行了仿真和实验验证。针对MMC系统的子模块故障问题，对无冗余备用的模块化多电平变换器容错控制方法进行了研究。提出基于零序电压注入方法的故障容错控制策略，讨论零序电压注入的可行性，在此基础上研究零序电压注入对MMC相间功率分配的影响。容错运行时的各个子模块电容的额定电压保持恒定，避免了电容电压波动对系统的暂态冲击和相间环流骤升，增强了MMC的故障穿越能力，并且无须增加额外的硬件成本。最后，论文研究了基于MMC拓扑结构的光伏并网功率调节系统的控制策略。首先分析了采用MMC拓扑结构的大规模光伏电站并网逆变器系统配置的技术特点和优势，为深入理解模块化多电平光伏并网功率调节系统的有功和无功的双向传输的可行性，给出基于空间矢量分析的系统运行模式的推导过程，研究了含无功和谐波补偿的光伏系统运行极限。为实现系统运行中的稳定控制，提出了一种基于标量脉宽调制的有功和无功功率协调控制策略，这种方法能够确保公共直流母线电压的稳定，，并有效地提高大规模光伏电站并网逆变器系统的利用率。
[Abstract]:In recent years, power electronic converter technology has been developed rapidly, and the demand for high voltage and high power energy conversion system is increasing. Multilevel converter breaks through the limitation of power semiconductor device capacity by improving the topology of the converter itself, and has become an ideal solution in the field of high voltage and high power power conversion applications. Modular Multilevel Converter (MMC) overcomes the drawbacks of traditional multilevel converters with its outstanding technical characteristics. It is the most attractive topology of multilevel converters in high voltage and high power power power systems. Methods, modulation techniques, fault-tolerant control strategies and their applications in the field of photovoltaic power generation are studied in detail.
Firstly, the capacitor voltage balance problem of MMC sub-modules is analyzed. Based on the operation mechanism of MMC, the generalized dynamic model of MMC is established, and two traditional capacitor voltage balance methods are analyzed and compared. The frequency of the sequence algorithm is improved in two aspects, which makes the sub-module voltage balance control method less dependent on the hardware, reduces the controller burden and reduces the switching frequency of the converter.
In this paper, two modulation techniques of MMC, stepped wave modulation and scalar pulse width modulation, are studied in depth. Firstly, the stepped wave modulation technique for MMC is studied. Aiming at the local convergence of Newton iterative method in solving the switching angle of MMC with stepped wave modulation, an improved hybrid particle swarm optimization algorithm is proposed. In the initial stage, particle swarm optimization algorithm is used to search the initial value of the switching angle equation randomly in the global scope, and then Newton method is used to quickly iterate to the exact solution. The expected output voltage is synthesized linearly by the level. The time of synthesizing vector can be realized only by calculating the duty cycle. The complicated trigonometric function operation and coordinate transformation can be omitted.
Aiming at the sub-module fault of MMC system, the fault-tolerant control method of non-redundant standby modular multilevel converter is studied. A fault-tolerant control strategy based on zero-sequence voltage injection method is proposed. The feasibility of zero-sequence voltage injection is discussed. On this basis, the influence of zero-sequence voltage injection on MMC inter-phase power distribution is studied. The rated voltages of capacitors of each sub-module under staggered operation are kept constant, which avoids the transient impact of capacitor voltage fluctuation on the system and the sudden rise of Inter-circulating current, enhances the fault traversing capability of MMC, and does not require additional hardware costs.
Finally, the control strategy of grid-connected PV power regulation system based on MMC topology is studied. Firstly, the technical characteristics and advantages of grid-connected inverter system configuration for large-scale PV power plants with MMC topology are analyzed in order to understand the two-way transmission of active and reactive power in modular multi-level PV grid-connected power regulation system. In order to realize the stability control of the system, a coordinated control strategy of active and reactive power based on scalar pulse width modulation (SPWM) is proposed, which can ensure the common straightness. The voltage of the bus is stable, and the utilization ratio of grid connected inverter system of large scale PV power station is effectively improved.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM46

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