【作者】 申科；

【导师】 蔡兴国；

【作者基本信息】 哈尔滨工业大学 ， 电力系统及其自动化， 2014， 博士

【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。更多还原

【Abstract】 In recent years, the power electronic converter technology has a rapiddevelopment, which cause the high power energy conversion system demand growsheavily. One perfect solution to breakthrough the limitation of power semiconductordevice capacity is improving the topology of the converter itself. With itsoutstanding technical features, the modular multilevel converter (MMC) overcomesthe defects of traditional multilevel converter successlly. So it is the most attractivemultilevel converter topologies in the high-voltage high-power electric powersystem. This paper have a deeply study about the modular multilevel powerconversion system which including voltage balance control methods, modulationtechniques, fault-tolerant control strategies and the application to photovoltaicpower generation system. The specific contents are as follows:The paper firstly analyzes the problems of sub-modules capacitor voltagebalance in MMCs. Starting from the operation mechanism of MMCs, a generalizeddynamic model of the MMC is set up. Based on analysis and comparison of the twotraditional submodules capacitor voltage balance methods, this paper presented amerge network based prediction sorting algorithm, making the improved efforts onthe optimization of the sorting algorithm efficiency and operating frequencyrespectively, by using a simple capacitor voltage estimation to determine the modeselection of pulse rotation and voltage sorting, the proposed method can reduce thedependence on the hardware level, as well as cutdown the controller burden and theswitching frequency of the converter.Then the staircase modulation and scalar PWM methods for MMC are studied.For the staircase modulation, to overcome the local convergence of the Newtoniteration method in solving the switching angles, a improved hybrid particle swarmoptimization (PSO) algorithm based staircase modulation strategy for MMC isproposed. This algorithm utilizes PSO to randomly search the optimal initial valuesof switching angles, which can accelerate the iterative speed at the next step of theNewton iterative processes. For the problem of scalarization of vector modulation,this paper also presents a scalar PWM algorithm with the capacity of capacitorvoltage balance. The algorithm based on the nearest level modulation (NLM)technique, which features a linearly synthesized output voltage by means of simplearithmetic calculations of duty cycles to determinate the switching sequences andthe duration times, saving the tedious trigonometric function calculations andcoordinate transformation. Simulation and experimental results verify thecorrectness and effectiveness of the proposed modulation methods. To solve the sub-module failure problem of MMC system with no redundancybackup, a zero sequence voltage injection based fault-tolerant control strategy forMMC is proposed. The feasibility of the zero sequence voltage injection isdiscussed, and on this basis the impact on the interphase power allocation of theMMC system is revealed. In fault-tolerant mode the rated capacitor voltage of eachmodule can keep constant, improving the system transient stability under the impactof the capacitor voltage fluctuation and avoiding the swell of the interphasecirculating currents. The strategy strengthens the fault ride-through ability of theMMC, and do not need to add additional hardware cost.Finally, the control strategy of the grid-connected photovoltaic (PV) powerconditioning system based on MMC topology is studied. The technicalcharacteristics and advantages of the large-scale PV power station which adopts thegrid converter system configuration of the MMC topology are analyzed. For thedeep understanding the feasibility of bidirectional active and reactive powertransmission of the modular multilevel PV power conditioning system, thederivation process of the system operation mode based on space vector analysis isgiven, and the system operating limits which contain reactive power and harmoniccompensation are studied. For the realization of system stability control, this paperproposes a scalar PWM based active and reactive power coordinated controlstrategy. This strategy can ensure the stability of the dc bus voltage, and effectivelyimprove the utilization rate of large-scale PV power station.更多还原