【作者】 李勋；

【导师】 陈坚； 杨荫福；

【作者基本信息】 华中科技大学 ， 电气工程， 2006， 博士

【摘要】 随着科学技术的发展,各种精密仪器和设备越来越多地得到使用,电力用户对电能质量的要求也越来越高。为改善配电系统电能质量问题,自上世纪八十年代末以来,基于电力电子技术的面向配电系统的FACTS技术(DFACTS)/用户电力技术(CUSPOW)得到了电力科研工作者的广泛关注。一系列的DFACTS元件相继得到研究和开发,其中由串、并联双变流器组成的统一电能质量调节器(UPQC)具有综合的电能质量调节能力,不仅可以改善电网输入电流的电能质量问题,也可以改善负载输入电压的电能质量问题,被认为是最有前途的电能质量调节器。本文针对三相四线制的UPQC,开展了以下一些研究工作,为此类电能质量调节器在配电系统中的实际应用进行了一些有益的探索。分析了三相四线UPQC的工作原理,指出UPQC的并联变流器受控为正弦电压源,而串联变流器受控为正弦电流源就可以实现UPQC对电能质量的综合调节。基于系统的理想控制作用及其等效电路模型,较深入地阐明了UPQC的静态工作特性,对串联变流器输出的补偿电压、并联变流器输出的补偿电流、不同工况下系统各部分吸收、发出有功功率/无功功率的情况以及串、并联变流器的伏安容量进行了详细分析,指出了在忽略串联变压器漏感的情况下补偿电压完全由负载电压及电网输入电压的幅值决定,补偿电流则受电网输入电压、负载电压及负载偏移角的影响,而变流器伏安容量则与负载功率因数、负载电流谐波畸变率、负载电压与电网输入电压的比值等因素有关。此外讨论了UPQC不同的主电路拓扑结构,指出其不同的应用场合及优缺点,并且基于三相三线制系统及三相四线制系统分析了串联变压器付方不同接法的适用性,指出了具有中线的串联变压器付方星型接法适用于三相四线制的UPQC系统。另外还介绍了一种基于MATLAB SIMULINK仿真环境的电路模型仿真技术,为后述的分析研究提供了有效的验证手段。分别在静止ABC及同步旋转dq0坐标系下建立了三相四线串联变流器及并联变流器的数学模型,指出了三桥臂构成的四线制串联变流器/并联变流器在三相坐标系下具有ABC三相独立而在dq0坐标系下具有dq轴耦合、0轴独立于dq轴的特性。研究了串联变流器的单独运行及其输入电流的控制。通过对非理想输入电压下串联变流器的分析,指出不平衡输入电压会在直流母线端电压中产生二次谐波的波动,反过来该二次谐波会在输入电流中产生三次谐波;而输入电压的N次谐波会在母线端电压中产生N-1及N+1次谐波,在输入电流中则产生相应次的谐波影响。为抑制输入电压不平衡及谐波的影响,本文提出了两种较为有效的控制策略:三相ABC独立控制及dq0轴控制,指出了两种控制策略下获取电流指令及设计电流控制器的一些特殊考虑。此外分析了直流母线端两组电容电压不平衡的原因,并提出了一种简单有效的抑制方法。仿真及实验结果表明针对串联变流器所提的各种控制方法是有效的。研究了并联变流器的单独运行及其输出电压的控制。首先讨论了非理想负载特性,指出负载的不平衡及非线性必然导致并联变流器输出电压的不平衡及谐波畸变。其次提出了一种适用于三相四线制变流器的三维空间矢量调节技术,克服了传统二维空间矢量调节技术在三相四线系统中应用的局限,仿真验证了该调节技术的可行性。最后对比了三相ABC独立控制及dq0轴电压电流双环控制的控制效果,指出采用所提的两种控制方法均可以获得较理想的平衡、稳定的电压输出,然而对输出电压中的负序分量及谐波的抑制能力有限。为此在dq0轴双环控制的基础上引入负序控制和谐波控制,或者在ABC独立控制中引入重复控制,则可以进一步消除输出电压中的负序分量和谐波。仿真及部分实验结果验证了所提控制方法的有效性。详细讨论了10kVA三相四线制UPQC实验装置的硬件电路设计和控制系统设计,给出了系统功率电路硬件参数的设计过程,以及串联变流器、并联变流器协调控制的双DSP控制系统原理及软件流程,提出了一种有效的系统投入与退出运行的策略。基于串、并联变流器的协调控制策略,对三相四线UPQC在各种工况下的运行进行了较全面的仿真研究及实验,详细分析验证了UPQC的系统性能,实验结果表明所提串、并联变流器的协调控制策略是有效的,较好地实现了UPQC对电网输入电流及负载输入电压的综合电能质量调节。更多还原

【Abstract】 DFACTS/CUSPOW, based on the power electronics technology for power distribution system, has drawn more attention since 1988. Unified Power Quality Conditioner (UPQC), composed of a parallel and series conversion system, is the most promising among all the DFACTS devices. It cannot only improve the network current quality but also the load voltage quality. This dissertation is dedicated to investigate the application of three-phase four-wire UPQC system in distribution network.The operation principle of three-phase four-wire UPQC system is analyzed. It shows that the combined power quality regulation of UPQC can be achieved by controlling the series converter as a sinusoidal current source and the parallel converter as a sinusoidal voltage source. The static operation principle is deeply analyzed based on the ideal control and the equivalent circuit model. The equations of system power flow, compensated voltage and current are established. The active and reactive power flow among two converters, power network and load are investigated under different operated conditions. Furthermore, the factors influencing system VA capability are also discussed. Two difference topologies are compared, including their application, merits and drawbacks. Moreover, the different connection types for secondary side of series transformer are analyzed in the three-phase three-wire or three-phase four-wire system. The analysis indicates that the Y-type connection with neutral line for series transformer is suitable for the three-phase four-wire UPQC system. A new simulation strategy based on Matlab Simulink environment is also introduced.Mathematical models of the three-phase four-wire series converter and parallel converter are established in ABC frame and dq0 frame respectively. The models show that each phase of the series/parallel converter is individual in ABC frame and 0 axis is independent of dq axis in dq0 frame. The current control strategies for series converter of UPQC are studied under ideal and non-ideal input voltage conditions. The influences of non-ideal input voltage are analyzed. The output dc voltage has the second harmonic and input current has the third harmonic due to the unbalanced supply. Nth input voltage harmonic results in the (N+1)th and (N-1)th harmonics in the dc voltage and Nth harmonic in the input current. In order to suppress the influence of non-ideal input voltage, two effective control methods are introduced. One is three-phase ABC individual control and the other is dq0 axis control. Special treatments and considerations for current controller are also indicated. The voltage unbalance between the two group capacitors is analyzed and a simple and valid method is provided. Simulation and experimental results verified the validity of the two control methods.The voltage control strategies for parallel converter of UPQC are investigated. The non-ideal load characteristics are discussed and their influences on output voltage are also indicated. Furthermore, a three-dimensional space vector modulation technique is introduced and its validity in three-leg four-wire converter is verified by simulation results. Several control methods are compared in order to suppress the influences of non-ideal load. These methods include three-phase ABC individual control, dq0 axis voltage and current dual loop control, dq axis negative sequence control, dq axis harmonics control, combined repetitive algorithms ABC control. Simulation and experimental results verified the effectiveness of these control methods.A 10kVA prototype of the three-phase four-wire UPQC is designed and built. The parameters of power circuit are designed and the coordinated control systems based on two digital signal processors (DSP) for series and parallel converter are introduced. Program flows are also provided. The instantaneous circuit simulation model of the whole system is built with Matlab Simulink. The basic characteristics of the UPQC are well verified by a large number of simulation and experimental results under fluctuating utility voltages and various linear and non-linear loads.更多还原