【作者】 杨辉；

【导师】 文福拴；

【作者基本信息】 华南理工大学 ， 电力系统及其自动化， 2010， 博士

【摘要】 由于电力工业放松管制、环境问题和能源危机的日益突出,特别是可再生能源和热电联产的开发利用,使得配电系统中分布式发电(Distributed Generation, DG)的份额不断增加。分布式电源常与配电系统相连接,在多个方面影响着配电系统的运行,其中保护问题已被认为是发展分布式发电的最大技术阻碍。传统的配电系统一般采用辐射状运行,且只有一个电源,潮流和短路电流的方向因而都是单一的,保护方案相对简单;分布式电源接入配电系统后,潮流和短路电流的方向会发生改变,传统的保护方案不再适用。随着配电系统中分布式电源数量和容量的不断增加,配电系统的结构和运行方式会更接近于输电系统,更复杂的保护系统设计因而就不可避免。然而,替换保护装置需要大量的投资,而且很难在短期内完成。在此背景下,深入、系统地研究含分布式电源的配电系统继电保护问题,对快速清除故障、恢复供电,减少停电损失以及分布式发电的发展,具有十分重要的理论和实际意义。虽然国内外对此作了一些研究,而且有些方法已经在实际中得到应用,但分布式发电技术相对较新,仍有很多重要问题没有得到很好的解决。本论文主要对配电系统潮流分析、分布式发电的特点及其对配电系统继电保护的影响、含分布式电源的继电保护协调等方面进行了深入研究。主要研究成果如下:1)为提高配电系统潮流计算的效率,提出了一种并行中断等待的前推回代算法。该方法对节点编号没有严格的要求,并将数字信号处理(Digital Signal Processing, DSP)技术中的并行流水线技术和单片机的中断等待技术应用于传统的前推回代法,使得计算时间明显减少。同时针对环网系统和有PV节点的情况对该算法进行了扩展。2)针对在配电系统潮流计算中,牛顿-拉夫逊法计算效率不高、收敛性不佳,前推回代法不便于处理系统环网和PV节点等问题,提出了两种改进的牛顿法:牛顿-下山算法和Broyden法。结果表明所提的两种改进算法在计算效率和收敛性方面都比常规的牛顿-拉夫逊法要好。所提算法对配电系统继电保护的在线快速调整具有十分重要的意义。此外,为了适应分布式电源接入配电系统的情况,对算法进行了扩展。3)概述了分布式发电的特点,并在此基础上着重阐述了可再生能源发电的一些基本特征。比较全面地建立了各类常见分布式电源的潮流计算模型,并主要从12个方面深入分析了分布式发电对配电系统继电保护的影响。4)为了解决分布式发电对配电系统过电流继电保护的影响问题,建立了一个描述过电流继电保护优化协调的混合整数非线性规划模型,并采用微分进化算法对该模型进行求解。该方法能够在满足协调约束的前提下,以最短的时间清除故障。5)为了解决可再生能源发电的间歇性和不确定性出力对继电保护的影响以及传统自适应保护的弊端,提出了一种离线计算的自适应过电流继电保护优化协调方法。该方法缩短了在线自适应调整继电器整定值的时间,并通过求解优化协调模型获得继电器整定值,使得保护系统在可再生能源发电出力的变化中始终保持最优状态。6)系统结构变化会使得流过继电器的故障电流发生改变,并相应地改变继电器的动作时间。针对这一问题,提出了一种能适应系统结构变化的过电流继电保护优化协调方法。建立了考虑系统结构变化的含分布式电源的继电保护优化协调模型,并采用改进微分进化算法对该模型进行求解。仿真结果表明所建立的过电流继电器优化协调模型能够较好的反映实际情况。最后对论文所做的研究工作进行了简要总结,并指出了这一领域有待进一步深入研究的问题。更多还原

【Abstract】 During the last two decades, the deregulation of the power industry, environmental issues, energy crisis and, in particular, a growing need for exploitation of renewable energy sources and combined heat and power (CHP) technologies have laid the foundations for an increased penetration of distributed generations (DGs) in distribution systems. In distribution systems with some DGs, as the DGs could impose great impacts on the system performance in many aspects both postitively and negatively, the protection issue is considered as the largest technical barrier for the further applications of distributed generations. Traditionally, distribution systems have been designed to operate radially with one supply source so both the power flow and short-circuit current are single-directional, which makes the protection issue easier. When distributed generation units are introduced in distribution systems, the power flow and short-circuit current would be changed to be bi-directional. As the share of distributed generation increases, distribution systems are more similar to transmission systems, thus more complex protection system design will be demanded. However, it is very expensive and time-consuming to replace the old protection systems. Given this background, it is very important to investigate the problems about protective relays in distribution systems with distributed generations. Although much research work has been done and some methods even developed and applied in the actual power systems, there are still many important issues to be solved. This dissertation focuses on several important, yet difficult, problems associated with protective relays in distribution systems with DGs, such as the power flow computation in distribution systems, the characteristics of distributed generations and their impacts on the protective relays in distribution systems, the optimal coordination of overcurrent relays in distribution systems with DGs. These problems are investigated systematically in this thesis and some significant results obtained.First, a new Back/Forward Sweep Method accommodating arbitrary numbing of nodes is developed, and applied to the power flow calculation in distribution systems. In the proposed method, an algorithm similar to the parallel-stream technique in digital signal processing (DSP) and the interruption-waiting technique in single chip microcomputers, named as the parallel and interruption-waiting method, is developed. The developed method is superior to some existing methods in the computational efficiency, and a further extension to deal with mesh networks and PV buses are made at last.Secondly, the Newton-Raphson power flow method is not very efficient and sometimes could even not converge when it is applied to distribution systems. The Back/Forward Sweep method is inconvenient to deal with mesh networks and PV buses in distribution systems although its convergence is good. Given this background, two modified Newton methods, i.e., the Newton-Downhill method and Broyden method, are developed. The research results show that the computational efficiency and convergence of the two proposed methods are much better than those of the Newton-Raphson method. The methods are also extended for distribution systems with DGs.Thirdly, the characteristics of DGs are described in detail, especially for the renewable energy generating units. The models of different kinds of DGs in power flow calculation are presented, and the impacts of DGs on protective relays in distribution systems investigated systematically from twelve aspects.Fourthly, the protective relay coordination problem in distribution systems is investigated with directional overcurrent relays taken as an example, and formulated as a Mixed Integer Nonlinear Programming (MINLP) problem. A mathematical model describing this problem is developed, and the well-developed differential evolution algorithm employed to find the optimal solutions. The proposed method could clear faults quickly with the coordination constraints respected.Fifthly, a novel adaptive protection scheme for the coordination optimization of overcurrent relays is proposed, and applied to settle down the impacts of the fluctuant power output of renewable generations on protective relays in distribution systems. In this scheme, the off-line calculation is employed to save the time for adjusting the relay setting. The relay setting could be obtained by the optimal coordination model, with an objective of keeping the protection system at the optimal state during the output power change of the renewable energy generation units.Sixthly, since the system configuration may change after a fault occurs, the fault current through the overcurrent protective relays could then change, thus the operation time of relays would be changed and further make the protection coordination problem more complicated. Given this background, a mathematical model, considering the system configuration change, for the optimal coordination of overcurrent relays in distribution systems with DGs is developed, and simulation results show that the developed method is correct and efficient.Finally, conclusions are made based on the research outcomes, and directions for further research indicated.更多还原