【作者】 杨嘉伟；

【导师】 毛承雄； 陆继明；

【作者基本信息】 华中科技大学 ， 电力系统及其自动化， 2013， 博士

【摘要】 跨区互联大电网的形成以及远距离重负荷输电线路的出现，在实现电力资源的优化配置、提高电力系统经济性和可靠性的同时，也带来了一些新的问题，譬如怎样解决大区电网通过极少数联络线进行弱连接的情况下出现的低频振荡以及远距离重负荷输电电力的稳定性问题等。常规晶闸管励磁系统只能通过调节励磁电压来增强电力系统阻尼，对于现代电力系统宽范围的功率振荡，很难有效同时抑制。因此，如何提高电力系统稳定性及电力输送能力的研究工作显得日益重要。智能电网的建设要求实现电力能源的高效利用和提高供电可靠性、改善电能质量。非线性、冲击性负荷的增长和间歇性分布式能源接入使得电能质量问题有日益恶化的趋势，而现代用户对电能质量问题变得越来越敏感，对电能质量要求更高，特别是工业企业，有必要采用有效手段为这些用户提供优质电力。另一方面，目前高压电动机很大部分没有配备变频调速系统，增加了电量的损耗，这也不符合国家提出的建设节约型社会、节能减排的思想。电压源型变换器因其良好的控制特性及灵活的结构，在电力系统中有着广泛的应用。本文研究了电压源型变换器在电力系统中一些新的应用场合，涵盖发电、配电、用电以及用户电能质量调节等方面，主要有以下几个方面的研究内容：首先阐述了基于电压源型变换器的励磁系统的基本原理和相对于传统晶闸管励磁系统的优点；建立了电压源型变换器励磁系统在单机无穷大系统下的数学模型，运用阻尼转矩方法确定了无功注入电流对发电机阻尼转矩的贡献，从而揭示了无功注入电流改善电力系统阻尼特性的机理；分别分析了电压源型变换器励磁系统励磁回路和无功注入回路对电力系统暂态稳定性的提升；仿真和动模试验结果表明，与常规晶闸管励磁相比，电压源型变换器励磁系统能够有效提高电力系统阻尼，增强电力系统静态和暂态稳定能力，并且具备提高远距离输电系统输送容量的能力。紧接着，本文提出了一种基于电压源型变换器的无输入变压器高压多相电动机调速系统，阐述了系统基本结构和工作原理，设计了相应的控制策略及DSP实现方式；该系统与具有独立定子绕组的电机配合使用，能够减小对电力电子器件耐压和通流的要求，省去了传统的移相变压器，从而减小成本和体积；在低压九相电动机实验平台上进行的实验结果验证了该系统的正确性和可行性。随后，本文介绍了基于电压源型变换器模块化结构的10kV/400V/500kVA电子电力变压器工业样机的研制情况，详细叙述了其控制构建与控制策略设计；提出了通过调节逆变器输出有功功率实现级联H桥整流器直流均压的新方案；设计了基于正、负序双环电流控制的三相有功功率调节方法；对电子电力变压器启动流程进行了分析和设计；仿真和低压实验表明所设计的控制策略能够维持电子电力变压器的正常运行，有效的保证直流电压平衡并适应电网以及负载不平衡等工况。最后，本文提出了基于电子电力变压器的有载调压装置，将电子电力变压器作为常规电力变压器的附属调节装置，可以大幅度减小电子电力变压器的体积和成本，并实现对电压的快速、连续调节；比较了电子电力变压器和常规电力变压器不同的连接方式，给出了两种具体的实现方案，设计了相应的控制策略；数值仿真和小样机实验结果表明，在指令指突变、供电电压波动、装置故障、负载突变以及供电电压不对称、跌落和突升等多种工况下，提出的有载调压装置都能够有效地将负载电压维持在给定值。更多还原

【Abstract】 The interconnection of large area power grids and the appearance of long-distancepower transfer lines with heavy loads contribute to the best use of power resources andimprovements of economy and reliability of power generation and transmissions. But at thesame time they also bring new issues into power system stability and control, especiallylow-frequency oscillations. The traditional thyristor excitation systems can only providedamping through field windings and it is difficult to tune the controller parameters tosuppress the large range of power oscillation frequency. Therefore, the research on how toimprove the stability and transfer capacity of modern power systems becomes more andmore important.High-efficiency utilization of electrical power and improving power supply qualityand reliability are important requirements for smart grids. The increasement of non-linearloads and high-capacity impact loads and the presence of distributed generation (DG) haveheightened power quality depravation. However, the requirement to the electric energyquality of users, especially industry enterprises, has been more and more rigorous. It isnecessary to provide high quality power supply for special users through effectiveapproaches. On the other hand, most of high voltage motors are not equipped with variablefrequency speed systems at present, which increases power lose and is not consistent withthe guiding ideology for energy-saving and emission reduction in Chinese electric powerindustry.Due to the good control characteristics and flexible structure, voltage source converter(VSC) has widespread application in power systems. This dissertation mainly studies on thenew applications of VSC, including power generation, distribution, consumption and powerquality regulation as follows:First is the research on the basic theory of VSC excitation system and its advantages ascompared to traditional thyristor excitation systems, and the Philips-Heffron model of asingle-machine infinite bus system with VSC excitation system is established. The dampingtorque analysis is applied to confirm the damping contribution of reactive current injection,so the mechanism of improvements of power system damping characteristics is revealed.The transient enhancements by excitation control and reactive current control of VSCexcitation system are analyzed separately. The simulation and physical model results showthat, VSC excitation system can improve damping significantly and improve power systemstatic-state and transient stability when compared with thyristor excitation systems; and it also has the ability to improve the maximum transfer capability of long-distancetransmission systems.Then, a VSC-based transformerless variable frequency speed system for high voltagemulti-phase motor is proposed in this dissertation, which decreases requirements on voltageand current stress of power electronic devices; so the size and cost can be reduced. Thecorresponding control strategy is developed and implemented in DSP. The experimentalresults in a nine-phase motor laboratory prototype show the correctness and feasibility ofthe proposed system.Then, this dissertation introduces the development of a VSC-modular-based10kV/400V/500kVA electronic power transformer (EPT), and discusses the control systemdesign process in detail. A new DC voltage balance method has been proposed for cascadedH-bridge converters through regulating the active power of inverters. The positive andnegative sequence current separate control strategy is utilized for operation of unbalancedthree-phase loads. The start-up process of EPT is also analyzed and designed. Thesimulation and low voltage prototype results show that EPT with the developed controlmethods could work normally, maintain the DC voltage balance, and adapt to unbalancedoperation.At last, a fast and continuous voltage regulator is proposed in this dissertation. EPTserves as an auxiliary voltage regulator for the line frequency transformer, so that the sizeand cost of EPT can be reduced significantly. Different connections between EPT and linefrequency transformer are compared. Two sample schemes are given and correspondingcontrol method is developed. The simulation and experimental results demonstrate that theproposed voltage regulator is able to maintain load voltages at the desired value effectivelyunder operation conditions, such as reference value change, voltage flicker, voltage rise,voltage dip, load changes and EPT fails.更多还原