【作者】 杨晓峰；

【导师】 郑琼林；

【作者基本信息】 北京交通大学 ， 电力电子与电力传动， 2012， 博士

【摘要】 随着电力电子技术的飞速发展,多电平变换器及其控制技术的研究正逐渐成为高压大功率电力应用领域的研究热点。模块组合多电平变换器(MMC)以其独特的结构优势,克服了传统多电平变换器的不足,同时在高压电力系统的电能质量问题尤其是负序问题治理方面具有良好的潜力。本文围绕MMC的关键技术、装置系统设计及其在电能质量领域的应用进行了深入细致的研究。论文首先分析了MMC的环流特性及影响环流的关键因素,建立了MMC的环流模型,研究结果表明环流无法完全消除,可通过改进控制策略的方法抑制其中的电压控制分量；相间环流的存在表明MMC可通过公共直流母线实现三相电网之间的有功和无功能量交换,这是MMC实现负序电流平衡应用的理论基础。在分析MMC环流模型基础上,提出了一种通用环流抑制策略,可有效抑制环流对桥臂电流、共模电压和公共直流母线电流低频振荡的影响。接着,论文研究了MMC系统关键参数的谐波解析式,提出一种基于改进型开关函数的谐波抑制策略,能有效抑制桥臂电流中的低次谐波分量,降低对桥臂电感的滤波要求。推导了MMC的数学模型,分析了电流解耦控制原理,为进一步研究MMC的动态和稳态运行特性提供了依据。论文研究了适于MMC特点的脉冲调制技术。对直流电压控制开环条件下多载波正弦脉宽调制技术及脉冲移相技术应用于MMC的输出特性对比研究表明,载波移相SPWM技术更适合于MMC的控制。研究了一种双调制波载波移相SPWM技术(DM-CPS-SPWM)及其在MMC中的具体实现方法,并提出一种载波循环分布的载波层叠SPWM(CD-ROT-SPWM)技术,实现了有功能量在功率单元中的近似平均分配。论文研究了MMC的直流电容电压控制策略。提出了两种无需外加直流供电电源的预充电控制方案,解决了MMC直流电容电压的同步初始化问题。分析了引起直流电容电压不平衡的根本原因,研究了一种基于自身平衡控制算法的直流电容电压控制策略。仿真和实验结果表明该控制方法具有良好的稳态和动态特性,实现了直流电容电压的稳定平衡控制。论文同时研究了MMC装置系统设计和实现中的关键问题。分析了MMC主电路参数的设计原则,开发了两套MMC样机实验系统及一套基于DSP和FPGA的数字化主从式控制系统。最后,论文完成了MMC在电能质量治理领域的研究实例。研究了基于MMC的STATCOM装置(M-STATCOM)的电路结构、工作原理和控制方案；确定了负序平衡应用下M-STATCOM的容量需求；仿真和实验结果表明,M-STATCOM不仅可实现感性／容性无功发生功能,也可实现对包括负序、无功和谐波在内的电能质量问题的综合治理,进一步验证了本文提出的控制策略的有效性和可行性。更多还原

【Abstract】 With the rapid development of power electronics technology, multilevel converter and its control strategies is becoming one of the hot spots in the field of high-voltage and/or high-power applications. Modular multilevel converter (MMC), features with the characteristics such as high modularity, low generation of harmonics, etc, is one of the next-generation multilevel PWM converters intended for medium-or high-voltage utility grid without line-frequency transformers. So the study on some key issues of MMC, experimental system design and its application in power quality controls, especially for the negative-sequence balancing, has been conducted in depth in this dissertation.By controlling the role of circulating current as current controlled voltage source (CCVS), the circulating current model of MMC was proposed. Analysis of the key factors affecting the circulating current shows that circulating currents cannot be completely eliminated, but can only be suppressed by means of control. The existing of the phase-to-phase circulating current component, which produced by redistributing the active power among three phases through the common dc-bus, shows that MMC is suitable for the need to achieve negative-sequence balancing applications. Based on the circulating current model, a universal circulating current suppressing strategy has been proposed and adopted for improving the power quality of leg current, suppressing the common-mode voltage and the low frequency oscillation appeared in the common dc-bus current.Detailed DC capacitor voltage has been developed using the switching functions concept. Moreover, a harmonic elimination technique based on the modified switching function is applied for suppressing the low-order harmonics in leg currents, which will further reduce the leg inductor requirement. On the basis of derivation of its accurate mathematical model, the current decoupling control theory is proposed, which provides the theorial fundamental for the further research on the steady-state and dynamic-state performance of MMC.The carrier phase-shifted SPWM (CPS-SPWM) is more suitable for MMC control compared with other multi-carrier SPWM techniques. So, this dissertation proposes a double-modulation CPS-SPWM (DM-CPS-SPWM) according to the output characteristics of MMC, and the implementation of DM-CPS-SPWM in MMC has been explained in detail. Moreover, a new power banlance control schemes of carrier disposition SPWM (CD-ROT-SPWM) technology based on carrier rotating diposition concept is proposed. The new CD-ROT-SPWM technology ensures the output power balance among different power units.Two pre-charging control methods without any external DC voltage sources are proposed to solve the DC capacitor voltage initialization issue. By analyzing of the key factors of the DC capacitor voltage imbalance phenomenon, a combination of the individual voltage control and the averaging voltage control strategy is proposed for DC capacitor voltages balancing control, which steady-and dynamic-state performance is verified by both the subsequent simulation and experimental results.Based on the analysis of the design principles of the main circuit component parameters, two sets of experimental prototypes and a set of DSP and FPGA-based digital master-slave control system have been designed and constructed. Representative experiments have been carried out on the experimental prototypes, and the testing results have verified the research work in this dissertation.The concept of M-STATCOM is introduced firstly. The study on the working principle and control scheme under two different conditions are conducted. Simulation and experimental results show that M-STATCOM can not only be controlled in static var generating condition for reactive power regulation purpose, but also be suitable for the comprehensive compensation of all the power quality problems such as negative-sequence balancing, reactive power compensation and harmonics suppression. M-STATCOM shows good prospects in electrical traction lines, medium-or high-voltage power distribution system, etc.更多还原