【作者】 刘黎明；

【导师】 康勇；

【作者基本信息】 华中科技大学 ， 电力电子与电力传动， 2006， 博士

【摘要】 FACTS技术的出现带给高压输电系统用户新的机遇和挑战,它改变了过去交流输电不能灵活控制和不能满足增长的电力需求的局面,是实现电力系统安全、经济、综合控制的重要措施,为复杂电力系统的稳定运行提供了一种很好的调节手段。在FACTS家族中最具有代表性的元件是STATCOM、SSSC、UPFC,其中STATCOM是最早实用化的FACTS装置,可以实现系统电压的稳定;而SSSC可以实现传输线路阻抗的调节且不会引发振荡;UPFC作为最灵活的FACTS装置可以单独做STATCOM和SSSC运行,又可以组合起来进行潮流调度和电压控制,因此有必要对这三种FACTS装置进行深入的研究。本文针对目前以上三种FACTS装置研究中存在的问题,进行了以下四个方面的工作。考虑到FACTS装置的成功应用要求对其所有可行的方法和它们的运行特性有一个清楚的了解,本文首先讨论了STATCOM注入电流运行范围、注入功率运行范围。建立了STATCOM的数学模型,分析了直流母线电容电压的暂态过程和系统电压平衡,在此基础上设计了相应的控制系统。安装在长距离输电线上的STATCOM能够支撑输电系统关键节点的电压,提高系统输电能力,因此本文讨论了不同的安装位置对STATCOM调节线路传输功率的影响。理论分析得出STATCOM安装在线路的中间时,其调节线路传输的有功功率最大,能够更好地提高系统的稳定性。考虑到STATCOM控制策略的选择是其能否更好地实现补偿效果的关键,本文讨论了目前应用于STATCOM的无功补偿控制模式和自动电压控制模式,认为对于配电系统来说自动电压控制模式是一个更好的选择。并且比较了STATCOM的三种自动电压控制模式:稳压控制模式、直接电压下垂控制模式和带电流补偿的电压下垂控制模式,发现如果允许电压下垂,在给定最大的电容和电抗值的情况下,STATCOM补偿的范围可以加大,可靠性更高。此外,通过分析可知,合理设计控制系统可以使得STATCOM能够增加系统的第一摇摆稳定性,抑制系统振荡。其次,讨论了SSSC注入电压运行范围、注入功率运行范围。建立了SSSC的数学模型,分析了直流母线电容电压的暂态过程,提出了一种无外部储能装置的SSSC自启动方案。SSSC的控制策略主要有直接电压补偿控制模式和阻抗补偿控制模式,本文通过对两种控制模式下SSSC补偿范围、功角特性的分析得出,SSSC采用直接电压补偿控制是最好的选择,给出了相应的控制系统设计。为了更为直观地了解SSSC对系统功率的影响,本文在系统接收端电压和发送端电压幅值、相位一定的情况下,给出了系统各部分有功和无功功率二维坐标平面图。对比了在改变同样大小的系统接收端的有功功率的时候,STATCOM和SSSC输出的无功功率的大小,最后得出在实际的运行条件下,SSSC工作效率更高。此外,在单机无穷大系统中分析了SSSC抑制系统振荡特性。再次,本文通过分析发现UPFC在潮流控制时对系统接收端和发送端相位都有较大影响,考虑了这个因素,本文更为准确的分析了UPFC的潮流控制能力。研究了UPFC系统中各部分的功率运行范围,通过数学推导发现系统各部分的功率受多个变量的影响,为了更直观地分析UPFC的运行轨迹,本文给出了UPFC系统各部分的二维功率运行平面和三维功率运行曲面,通过观察其二维功率运行平面和三维功率运行曲面可见,线路传输有功/无功功率的每一个运行点都是唯一与一个UPFC串联输出电压相对应的。但对于UPFC串联部分注入电网的功率而言,一定的功率运行点可能对应多个串联输出电压,因此要实现对电网潮流的有效控制,必须直接对线路电流或线路传输的有功/无功进行控制。通过分析UPFC在线路中的不同安装位置对其潮流调控能力的影响,得出UPFC的安装位置应根据实际要求综合考虑。考虑了UPFC装置内部各变量之间的关系,给出了UPFC的相对完整的控制系统,并联变换器采用了协调控制策略,串联变换器采用了交叉耦合控制和交叉解耦控制,并且通过仿真验证了控制系统的有效性。最后,建立了一个功率容量为15kVA的小型FACTS实验系统,结合教研室的技术力量和动态模拟实验室的条件,在380V的两个无穷大系统和800V的单机无穷大系统中,对STATCOM、SSSC和UPFC的性能作了实验研究,得到了大量有效的实验结果,为将来FACTS装置在实际系统中的应用奠定了坚实的基础。更多还原

【Abstract】 FACTS technology brings the users of high voltage transmission systems fresh opportunities as well as challenges. It appears to be one the most important alternatives to overcome both the inflexible condition of most of the power sytems and the continuously growing demand of power. It is an effective method to realize security, the economical, integrated control of power systems. It offers a good way to improve the stability operation of complex and interconnected power systems. This paper gives an overview of the emerging FACTS technology with emphasis on the STATCOM, SSSC and UPFC. Of the FACTS controllers of interest here, the STATCOM has the ability to increase/decrease the terminal voltage magnitude and, consequently, to increase/decrease power flows in the transmission line. The SSSC controls power flow by changing ehe series reactance of the line and is immune to classical network resonances. The UPFC is the most comprehensive multivariable FACTS controller.It can not only work separately as a STATCOM or a SSSC but also control the transmission line real and reactive power in the transmission line, improve the transient stability margins, damp power oscillations and provide voltage support. So it is necessary to further research the performances of FACTS controllers. To solve the problems existed in the research field of FACTS controllers above, this paper works in the four areas as listed below.The successful incorporation of FACTS controllers in the power systems requires a clear understanding of all possible approaches and their operating characteristics. In this paper, first, a systematic study is performed to derive operating areas of the shunt current injection and power injection of STATCOM. By the analysis of mathematical model, DC bus voltage and voltage balance of the STATCOM system, the corresponding control system is designed. STATCOM installed in the long transmission line can support key nodes voltage and improve transmission capacity of the power system. So this paper discusses how STATCOM for controlling the transmittable power in the transmission line depends on the location of STATCOM in the network. The analysis indicates that STATCOM installed in the middle line can control furthest the transmittable power in the transmission line and enhance transient and steady state stability of power systems. Considering the control scheme being the key to achieve better compensation, this paper discusses the reactive power compensation mode and automatic control mode of STATCOM. It can be concluded by analysis that the automatic voltage control mode is a better choice for the distribution systems. The automatic voltage control mode includes three types: the constant voltage control mode, the direct voltage droop control mode, the voltage droop control mode with the compensating current. By comparing three control modes above, it is shown that the linear operating range of a compensator with given maximum capacitive and inductive ratings can be extended if a regulation droop is allowed. On the other hand, it is reasonable to expect by analysis that, with suitable and fast controls, STATCOM can change the power flow in the system during and flowing dynamic disturbances so as to increase the transient stability limit and provide effective power oscillation damping.Second, a systematic study is performed to derive operating areas of the series voltage injection and power injection of SSSC. By the analysis of mathematical model, DC bus voltage, this paper proposes ans describes the self-startup technique of SSSC without energy storage. In this paper, two different compensation control modes of SSSC, the voltage compensation mode and the impendance compensation mode, are discussed. By analyzing compensation areas and power-angle characteristics of SSSC based on two above compensation modes, it can be concluded that the voltage compensation mode is better suitable for SSSC and the corresponding control system is designed. Under certain conditions, the certain magnitudes and phases of sending-end voltage and receiving-end voltage, this paper presents power operation plane plots of SSSC in a two-dimensional space. It provides an intuitionistic measure for understanding how SSSC impacts on the system power. This also compares the power ratings of STATCOM and SSSC when performing the same reactive power compensation job. As a result, SSSC is superior to STATCOM in actual operation. Moreover, the power oscillation damping performance of SSSC is analyzed in a simple single machine infinite bus system.Third, this paper discovers that the phases of the sending-end voltage and the receiving-end voltage change with the power flow in the transmission. Considering the factor, this paper accurately analyzes the power flow control performance of UPFC. Furthermore, the real/reactive power absorbed/injected by the components of the UPFC system during power flow changes is plotted in 2D and 3D space respectively. That provides an effective method to determine the power rating of the power conversion parts of the UPFC and judge the availability of the control scheme for UPFC. By observing the power map, it can be found that every point of the transmission real & reactive power is corresponding to a certain voltage injected by the series part of the UPFC. However, for the power map of the injected power by the series part of the UPFC one power operating point may corresponding to more than one voltage injected by the series part of the UPFC. Therefore, it is necessary for effectively controlling power flow to directly control the transmission line current or real/reactive power in control system. By analyzing the effect of placement of UPFC to power flow control, it is conclude that placement of UPFC should be considered based on actual demand. Considering the internal relations among the variables of UPFC, a relatively complete control system is designed: a coordinated control scheme is used in shunt converter, cross-coupling control scheme and cross-decoupling control scheme are used in series converter. Simulation results show the effectiveness of the proposed control system.At last, a 15kVA FACTS experimental system is established in this paper. Combining office technology and the dynamic simulation laboratory conditions, this paper studies the performance of STATCOM, SSSC, UPFC in two infinite bus systems at 380V rating and a simple single machine infinite bus system at 800V rating. And abundant effective experimental results are gotten in this paper. These works lay a sound foundation of the powerful FACTS controllers for future application.更多还原