【作者】 唐爱红；

【导师】 程时杰；

【作者基本信息】 华中科技大学 ， 电力系统及其自动化， 2007， 博士

【摘要】 在世界经济迅猛发展和不断融合的过程中,电力系统为了适应经济快速增长所带来的对用电需求的增加,全球主要国家和地区的电力系统目前都沿着高电压、大容量、大规模、远距离输电的方向发展。由于我国煤炭资源与用电主要负荷的分布不均现象,以及多条±500kV直流输电线路的建立,在我国实现西电东送和全国联网的呼声越来越高并且逐步成为可能。如何保证如此庞大而复杂的电力系统稳定可靠的运行已经成为目前电力工作者致力研究的一个主题。FACTS技术是将电力电子技术、现代控制技术及计算机技术与电力系统相结合的产物,它通过对输电系统的母线电压、输电线路电抗和相位角的控制,快速实现线路的有功和无功潮流调整,输送功率的合理分配,可以降低功率损耗和发电成本,提高交流系统的稳定性和传统交流输电系统的传输能力,充分利用输电线路的输电能力,满足电力系统安全、可靠和经济运行的目标。统一潮流控制器(UPFC)是FACTS家族中的一员,它以能同时对电力系统进行潮流调节、电压控制和振荡抑制的综合功能而倍受电力工作者的青睐。1998年世界第一台UPFC装置在美国Inez变电站的投入和成功运行不仅证明了UPFC在理论上的正确性和在实践上的可行性,也证明了UPFC能给电力系统带来巨大经济效益。但对如何实现UPFC可参考资料的透露却微乎其微。本文从各种参考文献入手,在总结前人所进行工作的基础上,进行了如下几项工作:首先,在分析UPFC工作原理的基础上,采用输电线路的热稳定电流和UPFC串联侧注入母线最大电压的乘积关系确定了UPFC的装置容量,考虑系统运行母线电压水平的限制和线路传输功率极限的限制,确定了UPFC的各项运行约束指标;使用电力系统暂态仿真软件PSCAD/EMTDC,结合所确定的UPFC各项运行约束指标,建立了包含基于IGBT的UPFC装置、基于SPWM电源逆变器的装置级控制系统、基于常规PI控制的系统级控制和以单机经双回线向无穷大系统送电的电力系统等详细动态仿真模型;分别进行了UPFC在电力系统稳态时对电力系统的有功功率调节、无功功率调节和系统母线电压控制等功能的仿真分析,UPFC装置直流母线电压的变动对UPFC性能影响的仿真分析,在无UPFC装置的输电线路上发生三相短路时UPFC对电力系统潮流、电压和振荡影响的仿真分析以及线路上发生不对称单相短路时UPFC对电力系统潮流、电压和振荡影响的仿真分析。论文建立了能完全反映UPFC各种运行约束条件和动静态运行特性的简化动态模型,采用两个等效的可控电压源表示UPFC的串并联变流器,考虑了串并联变流器与输电系统间的有功功率交换和两变流器间通过直流电容相耦合的有功功率平衡关系,推导了UPFC直流电容的动态等效模型;为保证模型的精确性,适当考虑了UPFC的线路和变流器功率管的电阻损耗,用一个与直流电容相并联的等效电阻表示。模型的建立为UPFC控制系统的研究工作提供了基础。充分利用模糊控制对控制对象依赖程度小和强鲁棒性的特点,结合常规PID控制器的优点,设计了一个以线路有功、无功功率的误差及误差变化率为输入的,以PI控制的比例系数和积分系数为输出的,可以对控制器参数进行自动调整的自适应模糊PI控制器;采用仿真分析的方法,确定了自适应模糊PI控制器的模糊控制规则和量化因子及比例因子参数;同时对控制器的性能进行了详细的仿真分析。运用PSS的基本原理,设计了一个以线路有功功率变化量为输入的比例式UPFC辅助控制器,将辅助控制器的输出同时使用于UPFC并联侧的母线电压控制器和串联侧的线路有功功率控制,可以有效抑制发生在输电线路上的低频振荡,还有利于控制受到大扰动时的电力系统。为了验证UPFC的工作原理和对实际UPFC装置性能的深入研究,研制了一套15kVA的UPFC装置及相应的控制系统;在单机无穷大动态模拟电力系统上分别进行了基于常规PI控制器和自适应模糊PI控制器的UPFC实验研究。该项工作的完成为今后对UPFC的深入研究提供了一个有用的实验平台。更多还原

【Abstract】 With the fast development of the worldwide economy, to meet the increasing demand of the power energy, modern power systems are developed rapidly characterized by the high-voltage, the large quantitative capacity, the large-scale spreading of area and the long-distance transmission. In our country, most of the power recourse is located in the north-west area, but the main power energy consumer is massed in the south-east area. As a result, it is necessary to transmit large amount of electrical power over long distance from the north-west to the south-east. How to ensure the stability and to enhance the reliability of the power systems is the main challenging problem.FACTS(Flexible AC transmission systems) which combines the techniques of the power electronics, computer, modern control theory provides powerful capability of regulating the active and reactive power flow, depressing the power losses and generation costs of the transmission line, improving the stability of the AC transmission systems of power system by controlling the bus voltage, transmission reactance and power phases. Therefore, it attracts great attention in the recent years.UPFC (the unified power flow controller) as one of the most powerful FACTS devices, can regulate the power flow, maintain the bus voltage and damp the oscillation of the power systems becomes the focus of the current research. The first practically used UPFC was realized in the Inez power station of America in 1998. Its successful operation demonstrated the effectiveness of the UPFC. However, very few information can be found from the publications about the details of the UPFC.By reviewing the published literatures about the UPFC, this thesis aims to investigate the performance of the UPFC by both the digital simulation as well as the experimental tests. The main work done by this thesis is as follows:Firstly, based on the analysis of UPFC, the capacity of the UPFC is determined by use of the multiple restriction including the thermal limits of the transmission line and the limits of the voltage injection by the series converter, Also, details about the operation parameters of the UPFC are determined with the consideration of the limits of the bus voltage and the power transmissions. Using the PSCAD/EMTDC software and the above mentioned results, the operation limits of the UPFC are investigated and a detail dynamic model for the UPFC is obtained which includes IGBT based converters, SPWM based converter control systems, a traditional PI based controller and a single-machine infinite-bus power system By use of this model, power flow and voltage regulation characteristics as well as the transient stability recovering ability of the UPFC on the power system in the steady state and transient state are investigated by the simulations.For the purpose of the promising efficiency, this thesis taking the controllable voltage sources as the series and shunt converters, this model includes all of the UPFC operating limits and can describe in detail of the static and dynamic properties for the UPFC. With the consideration the power exchanging between the AC power system and the converters and the balances of the active power among the two converters and the DC capacitor, this paper deduces a dynamic equivalent model for the DC capacitor of the UPFC. In order to guarantee the accuracy of the equivalent model, the losses of the device circuits and the IGBT is modeled by a resistance connected to the DC capacitor in shunt equivalent circuit. This simplified dynamic equivalent model of UPFC will be used in the study of the control system in the following chapter.Fuzzy control algorithm has an advantage of less depending to the accuracy of the mathematical model for the controlled system. It is used together with the conventional PID in this thesis. Therefore, a self-adaptive fuzzy PI controller is obtained and used for the UPFC. In the proposed control, two kinds of feedback inputs are used. One of the inputs is the errors of the line active and reactive power and the other one is the variation of the errors. The outputs of the control are feed forward to the control system.. A set of the fuzzy rules are obtained using the simulation results given in chapter 2, which is used to determine the corresponding coefficients of the fuzzy-logic controller. The simulations of both the steady state and transient state are carried out to investigate the characteristics of UPFC with the proposed controller. Comparison is made by the simulation results between the UPFC controlled by proposed and the conventional PI controller.Based on the principle of PSS, a supplement controller, which uses the variation of the power flow in the transmission line as the input and the output is used to control the bus voltage and the active power transmission to damp out the low frequency oscillation of the power system and to enhance the power system transient stability after large disturbances. Satisfy results are obtained and given in the thesis.For the purpose of demonstrating the effectiveness of the UPFC and the proposed control, a 15kVa experiment prototype UPFC is developed and tested in a laboratory physical test environment. Theoretical result obtained in the above mentioned chapters are verified. Details of the prototype UPFC and the controller are all given in the thesis together with the test results. Also, the performance of the two kinds of PI control is compared.更多还原