【作者】 朱鹏程；

【导师】 陈坚； 康勇；

【作者基本信息】 华中科技大学 ， 电力电子与电力传动， 2005， 博士

【摘要】 自80 年代以来基于电力电子技术的FACTS 技术得到了广泛重视和研究。在众多FACTS 元件中由串、并联双变换系统组成的统一潮流控制器(UPFC)不仅可以独立作为STATCOM 和SSSC 运行,而且组合在一起构成UPFC 时能实现对所在线路有功、无功潮流的独立控制,因此具有独特的研究价值。本文针对目前UPFC 研究中存在的问题,进行了以下六个方面的工作。首先,本文详细分析了UPFC系统在潮流调节的过程中各部分吸收、发出有功/无功功率的变化情况,并首次在三维空间中绘出了各部分的功率运行曲面,为有效选取UPFC各部分的功率容量和判断潮流控制方案的可行性提供了一个直观的手段。通过观察UPFC输出侧线路潮流的运行曲面,可以发现功率曲面上的每一个运行点都是唯一的与一个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。因此只能通过控制UPFC串联输出电压来控制线路传输功率潮流。通过对UPFC电压控制特性的讨论得出,为了维持UPFC输入端电压恒定必须由其并联部分补偿适当的无功功率,其关系近似呈一种线性关系。同时分析表明,在UPFC输入端电压幅值维持不变的情况下,UPFC输出端线路无功传输潮流的变化和UPFC串联部分吸收的无功功率实际上是由UPFC的并联部分提供的; UPFC端电压幅值的控制既可以从并联侧控制也可以从串联侧控制,同样线路传输无功潮流也可以有两种不同的控制手段。其次,针对UPFC 并联变换器的运行要求,指出了其主电路参数选取过程中应注意的问题并给出了一套有效的主电路参数设计方案。通过选择合适的电路参数可以使得并联部分更容易达到相应的控制目标,为整个UPFC 系统的平稳运行提供了保证。在此基础上,本文给出了相应的解耦控制方案和控制器设计方法并针对并联变换器单独作为STATCOM 运行的情况讨论了几种不同的电压控制模式及效果。此外,还讨论了SSSC 和DVR 的控制系统及其在实际系统中平滑切入电网的过程,并通过建立SSSC 的小信号模型设计出相应的SSSC 直流母线电压控制器。实验结果表明了所设计的控制系统具有良好的性能。SSSC 到底会不会引发次同步振荡?目前有不同的说法,本文通过分析和实验表明SSSC 在阻抗模拟模式下若控制不适当则有可能引发次同步谐振。最后,本文对目前所提出的几种主要UPFC 潮流控制方法做出了详细的分析和更多还原

【Abstract】 Since 1980’s FACTS system, which is based on the technology of power electronics, have gotten more and more attention. Among the FACTS devices Unified Power Flow Controller composed of a parallel and a series conversion system can not only work separately as a STATCOM or a SSSC but also control the real and reactive power flow alone the transmission line independently. Such characteristics attract the eye ball of the researchers. To solve the problems existed in the research field of UPFC, this paper works in the six areas as listed below. First, the real/reactive power absorbed/injected by the components of the UPFC system during power flow changes is plotted in 3D space. 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. So only the series voltage injected by the series part of the UPFC can be controlled to manipulate the transmission power flow. According to the discussion of the voltage control characteristic of UPFC, to maintain the input port voltage of the UPFC constant, the parallel part of the UPFC must compensate proper reactive power and there is a linear relationship between the output reactive power of the parallel part and the input port voltage amplitude of the UPFC. On the other hand the analysis also indicates that when the voltage amplitude of the input port of the UPFC is controlled to be constant during the power flow variation, it is the shunt part of the UPFC that provides all the reactive power needed by the transmission reactive power variation and the variance of the reactive power absorbed by the series part of the UPFC. And it is shown that the input port voltage of the UPFC can be controlled by the shunt part of the UPFC as well as by the series part of the UPFC, while the reactive power flow of the transmission line can be controlled in two different way too. Second, according to the operation requirement of UPFC and STATCOM this paper presents effective methods and formulations to calculate and select the best circuit parameters for the parallel part of the UPFC. With the proper circuit parameters it is easier for the parallel part to realize it control target, and that ensures the stable operation of the UPFC system. Based on the analysis, the decoupling control strategy and the controller design procedure are presented. With the proposed control scheme and control parameter the parallel part works separately as a STATCOM is tested with experimental works, and the effects of several voltage control schemes are discussed. Third, in this paper the control system of the SSSC/DVR and the procedure of inserting the series device smoothly into the transmission line are discussed. The little signal model of the SSSC is established and used to design the dc bus controller for the SSSC. Experimental results indicate that the control system has good performance. Would SSSC cause Sub-Synchronous Resonance? Till now there are different opinions. In this paper analysis and experimental works are done to prove that SSSC will cause SSR with non-proper control in the capacitor simulation mode. At last, the main power flow control strategies for the UPFC are analyzed and compared. Simulation and experimental works are done to test the conclusions. The results prove that the cross coupling power flow control scheme has slow dynamic response performance, and the influence between the real and reactive power flow is small. The cross decoupling control scheme gets a faster response but during the power flow changes there will be a large power flow variation caused by coupling phenomenon. Coordination control add forward-feed signal to the real & reactive power reference of the parallel part of the UPFC, and it can improve the dynamic performance of the dc bus voltage control and the input port voltage control, however this control method can not improve the reactive power flow dynamic control performance. Based on the real & reactive power balance analysis, this paper proposes a novel control scheme for UPFC firstly, which is different to the conventional strategies. In this control scheme the parallel part of the UPFC is used to control the dc bus voltage and the transmission reactive power, the series part of the UPFC is applied to control the UPFC input port voltage and the transmission real power flow. Because the series part controlsthe UPFC input port voltage directly and acts as a DVR with real power flow control function, a less input port voltage variation is expected during the power floe changes. On the other hand because the reactive power output of the parallel part is controlled directly to manipulate the transmission reactive power flow, a faster reactive power flow performance is expected. Simulation and experimental works proved the effectiveness of the proposed control scheme, although this scheme does nothing to improve the dynamic performance of transmission real power flow control, its reactive power flow control performance is better than cross coupling control and there is little real power variation caused by coupling during the reactive power changes. Analysis indicates that this control scheme is insensitive to the transmission line parameter variation, so this proposed control scheme is an effective method to improve power flow control performance, when the transmission line parameter is not properly known. In this paper a hardware experimental system is established to test various control schemes of UPFC. And those are the first effective experimental results gotten in the nation. These works study the control characteristics of UPFC and make a useful exploration of the powerful FACTS device for future application in China.更多还原