【作者】 杨晓宪；

【导师】 张保会；

【作者基本信息】 西安交通大学 ， 电气工程， 2006， 博士

【摘要】 随着电力改革的不断深入,对10kV中压配电网络的运行管理提出了越来越高的要求。配电自动化,远方抄表,用户负荷管理和需求侧管理等配电网管理系统正在逐步应用和工程实用化。制约配电网管理系统发展的技术上的瓶颈之一,是缺乏一种具有较高性能价格比的数据信息交换平台。电力线通信是以电力线作为传输信道,实现数据通信和信息交换的一种通信方式。10kV中压线路从变电站出发可以直接延伸到线路上的任何一个用户节点,由10kV电力网络构成的电力通信系统在传输信道的经济性、网络的覆盖面等方面存在着巨大的优势,是一种极具竞争力的配电网管理系统的信息交换平台。然而,电力网络以工频能量的传输、分配为目的,是一种典型的总线型结构。对于高频通信信号的传输而言,这种结构上的特点以及工频负荷的存在,导致电力线信道表现为非常恶劣的传输环境,使得电力线通信的研究具有较大的挑战性。本文旨在研究10kV中压电力网络的信道特性。在基于两个具有一定代表性的10kV中压电力网络现场测量结果的基础上,结合实验室的有关实验,在40kHz-2MHz的频率范围内,对10kV中压电力网络信道的主要特性包括噪声、阻抗、传输等方面进行了初步探索,获得了一些具有一定普适意义的结论,建立了相应的信道模型。主要研究内容包括:⑴根据10kV电力线信道的拓扑结构和基本特征,提出了基于10kV电力线信道物理特征的基本信道模型,讨论了表征信道特性的主要参数和测量方法。其中利用电力环网线路直接测量信道传输函数H(f)的幅频响应和相频响应的新方法,解决了一直难以处理的长距离物理信道相频响应频域直接测量的问题。同时采用平移矢量网络分析仪的校准参考面的方法,这种方法可以有效地消除耦合器等辅助设备对实际信道测量参数的影响,提高测量效率和数据处理精度。⑵对噪声特性进行了较为深入和全面的研究,初步认识了10kV电力网络信道的噪声水平,噪声的各种分布特性,以及电网运行状态与噪声特性的关系。研究表明,10kV电力网络的噪声水平与电网的结构、容量和负荷等有关,一般高于低压电力网络。噪声功率谱通常呈指数衰减分布,当与高一级电网间存在着较多的交叉跨越时,分布规律将受到高一级电网噪声特性的影响。在10 kV电力线上,供电端(首端)的噪声水平略高于受电端(末端),但基本上可以看作是沿线均匀分布的。相相间耦合的差模噪声一般不大于与其相关的两相单独对地耦合时的共模噪声,甚至可能远低于后者。⑶建立了信道噪声中背景噪声统计模型,并通过Pearsonχ2检验验证了模型的适应性。在时域,10kV电力网络的背景噪声服从不同的统计规律。在低频较宽的频段内,与通常所推测的Gaussian分布不同,无论是有色噪声还是白噪声,都服从Nakagami-m分布。当频率达到数十兆赫兹数量级时,则服从Gaussian分布。在频域,不同的网络可能具有不同的噪声模型,但表征它们的变化参数仍然服从Nakagami-m分布。⑷研究了10kV电力网络的阻抗特性,为通信耦合设备阻抗参数的优化设计和信道的阻抗匹配提供了理论上的支持。研究表明,10kV电力线信道的阻抗特性与系统的结构和配置有关。在1MHz频段以下,输入阻抗的动态范围为数十至数百欧姆。随着频率的增加,动态范围逐渐减小,最后趋于数十欧数量级,且基本呈纯电阻性。网络各个节点处的输入阻抗有所不同,但特性阻抗基本上是相同的。10kV电力线信道的输入阻抗基本不随着工频负荷而变化。变电站10kV母线上的电容器组的投切对输入阻抗没有影响。差模耦合的特性阻抗略大于共模耦合,但输入阻抗的动态范围也大于共模耦合。⑸对10kV电力线信道的宽带传输特性作了初步研究,包括信道的幅频响应和相频响应特性,信道的频率色散和时间色散等主要涉及数字通信方式的信道参数。10kV电力线信道呈典型的多径传输特征,信道的频率响应是振荡衰减的。在发送端/接收端间无分支线路、配电变压器等设备的情况下,相地耦合时,每km的衰减功率为10-20dB。信道的相频响应基本上呈线性相位。信道的窄带衰落服从Nakagami-m分布,衰落深度为3-10dB。信道的时变性较弱。当通信速率达到kbps数量级及以上时,可以作为时不变信道处理。信道是时间色散的,信道的rms时延扩展和相干带宽均与具体的网络结构有关,大致是数十微秒和数十千赫兹数量级。⑹深入研究了10kV电力网络信道的传输路径损失,提出了信道传输路径损失模型。研究表明,对信道路径损失影响最大的是TX/RX间接入的电气元件,例如配电变压器、分支线等所引起的分流衰耗。网络其他部分对信道间路径损失的影响较小。变电站母线上的并联补偿电容器组对信道路径损失几乎没有影响。通过分支线接入信道的元件的等值阻抗将被分支线本身所“平滑”。当元件阻抗值较低时,这一“平滑”效应有利于降低其对信道产生的分流衰耗。相相耦合方式的传输路径损失较相地耦合大致低5-15dB。更多还原

【Abstract】 With the power innovation going further, a more strict operation management of the 10kV medium voltage distribution network is required. The distribution power network management system, including the distribution automation, remote metering, load management and the demand side management is being applicable and engineering practicable. On of the technical bottlenecks constraining the development of distribution power network management system is the absence of a data exchange platform with higher ratio of performance to cost. Power line communications use the power network as a transmission channel to realize the data transmission and information exchange. As a more competitive information exchange platform of the distribution power network management system, power line communications take many advantages on the economic transmission channel and network coverage. Nevertheless, the traditional power network serves for the energy transmission and distribution of the mains frequency and exhibits a typical bus structure. For high-frequency communicating signal transmission, such structure and the existence of load of mains frequency result in a hostile environment for signal transmission. Such a hostile channel makes the research of power line communication being more challenging.This paper mainly focuses on the channel characteristics of the 10kV medium voltage power network. On the basis of empirical data obtained from two representative 10kV medium voltage power networks, and with the support of laboratory experiments, the basic channel characteristics are examined, including noise, impedance and transmission properties of the 10kV medium voltage power networks over the frequency ranging from 40kHz-2MHz. Some meaningful conclusions are exposed, and the corresponding channel model is established. The main studies include:(1)Based on the topology and some fundamental properties of the 10kV power line channel, a basic model representing the physical properties of the 10kV power line channels is proposed. Furthermore, the parameters describing the channel properties and practical research methods are discussed. The methods for measuring the channel parameters are examined. And a new approach which uses the electrical loop wires to directly measure the channel transfer function H(f)and obtains the amplitude response and phase response, is provided to deal with the direct measurement of phase response for a line of long length. This problem has puzzled the researchers for a long time. Also, the method of moving the reference plane of the network analyzer is used for the first time. This method can efficiently eliminate the impacts on measuring the practical channel parameters introduced by the auxiliary equipments such as coupling devices, which will improve the measurement efficiency and accuracy of the data process.(2)A relatively deep research on the noise characteristics on the 10kV power network is carried out. The noise level of the 10kV power networks depends on the power network structure, configuration, and loads. It is often higher than that of the low voltage power networks. The noise power spectrum density usually follows the exponential distribution. However, if the power lines cross with the lines of higher voltage class power networks, the distribution is impacted by the noise from the higher voltage power network. On the 10kV power line, the noise at the power supply side (head side) is a little higher than that at the receiving end (tail side). Whereas, the noise distributes uniformly. The system impedance at the busbar absorbs some noise power. The noise level of phase to phase coupling is usually lower than or at least not greater than or even much lower than those of the related two single phase to ground coupling, respectively.(3) The background noise is statistically analyzed and corresponding statistical models are established in the time domain and the frequency domain respectively. And the Pearsonχ2 test is used to estimate the model’s application. In the time domain, the background noises on the 10kV power network follow different statistical distribution. At lower frequencies and a broad band, both the white noise and colored noise follow the Nakagami-m distribution which is different with the commonly assumed Gaussian noise. Only at frequencies on the order of tens of megahertz, the noise distribution obeys Gaussian. In the frequency domain, even there are distinct functions to fit the spectrum profiles of different power networks, their parameters, however, still follow the Nakagami-m distributions.(4) The impedance characteristics of the 10kV power network are studied. The impedance characteristic is in correlation with the power system structure and its configurations. Below 1MHz, the dynamic range of the input impedance is from several tenths of ohms to several hundreds of ohms. The dynamic range is becoming narrower with frequency and tends to the order on several tenths of ohms at last, where it exhibits pure resistance. The input impedances at each network node are different but their characteristic impedances are the same. The input impedance of the 10kV power network is greatly steady and scarcely varies with the loads working at mains frequency. The capacitor group connected to the bus has no influence on the input impedance. The input impedances in differential mode and common mode coupling are almost symmetric. The impedance value in differential mode coupling is higher than that in common mode coupling. However, the dynamic range of the former one is larger.(5) A pilot study on the transmission characteristics of the 10kV power line channel is carried out. A 10kV power line channel has the characteristics of a typical multi-path propagation. The channel frequency response attenuates with oscillations. If there are no branches and distribution transformers between TX/RX, the power attenuation is about 10-20dB/km in phase to ground coupling.The corresponding phase response is linear. The narrowband fading follows Nakagami-m distribution. And the fading depth is 3-10dB. In general, the time variance of the channel is weak. If the communication data rate is up to kbps, it can be regarded as a time-invariant channel. The channel is time dispersed. Both the rms delay spread and coherence bandwidth of the channel are related to the practical power network structure. The corresponding values are about ten microseconds and several tens of kilohertz respectively.(6) Based on the transmission line theorem, the path loss over the 10kV power network channel is discussed. A simple path loss model is proposed for engineering analysis. The most severe impact on the path loss depends on electrical equipments connected between TX and RX. These equipments including distribution transformers and branches introduce some drain losses. Other parts of the network have little impact on the path loss. Also, the parallel compensation capacitor groups connected to the bus have no effect on the path loss. The equivalent impedance of any component wired into the network through a branch has been smoothed by that branch. If the impedance of the equipment is lower, thus smoothness favors the reduction of the drain loss caused by the corresponding equipment. The path loss is 5-15dB lower in phase to phase coupling than that in phase to ground coupling.更多还原