多频带自适应技术在电力载波方面的研究

智能电网的数字化和信息化建设,对电力载波通信技术提出了更高要求。传统协议标准如G3-PLC已难以适用于复杂、时变、差异性的电网信道,需要对其带宽标准和信道容量进行改进。正交频分复用技术(Orthogonal Frequency Division Multiplexing,OFDM)是电力载波通信的主流方法,可以在其固定带宽的基础上进行多频带改造,实现带宽的自适应选择和信道容量的扩增。为此,提出一种基于OFDM的多频带自适应技术,以实现在7. 8 kHz～10 MHz跨频带范围内自适应选择合适的工作频率和通信带宽,来完成信息的有效传输。从现场的低、中压测试结果看,所提出的多频带自适应技术能够有效增大信道容量,并提高数据传输的可靠性和电力载波通信的线路覆盖率。     

Robust Stability of Networked Load Frequency Control Systems with Time-Varying Delays

In deregulated power system scenario coupled with smart grid technology, for networked load frequency control (LFC), an open communication structure, owing to low cost and flexibility, is preferred over dedicated networks in the feedback control loop for transmitting/receiving the data between the geographically displaced power system and the control center. In such a control scheme, closing the feedback loop through an open communication channel, in turn, introduces two additive time-varying delays of dissimilar characteristics in the feedback path. These delays degrade the performance of the closed-loop system, and exert a destabilizing effect on the overall system. In this paper, using Lyapunov-Krasovskii functional approach, a less conservative stability criterion is presented to ascertain delay-dependent stability of such network-controlled LFC systems with two additive time-varying delays in the feedback path in the presence of uncertain load disturbance conditions. Unlike the existing results, which are derived by combining these two delays into one, the proposed result considers the two delays as separate entities thereby imparting more generalization into the stability analysis. The effect of unknown exogenous load disturbance is incorporated by mathematically modeling them as a bounded non-linear time-varying function of current and delayed state vectors.     

An efficient cooperative sensing scheme with bandwidth-limited control channel

The conflict between scarcity of spectrum resources and low spectrum utilization motivates the concept of cognitive radio, which allows secondary unlicensed users to borrow temporally unused spectrum bands from primary licensed users. Spectrum sensing is one of the key functionalities that enable spectrum hole discovery and interference avoidance. As single user spectrum sensing may experience performance degradation in harsh wireless environment due to fading and shadowing, user cooperation is introduced to exploit spatial diversity for better sensing performance. However, local sensing results must be transmitted via a control channel. The advantage of cooperative sensing can be compromised by bandwidth limitation of the control channel. To overcome this, a benching cooperative sensing scheme is proposed in this paper. This scheme can reduce time overhead of sensing information exchange under a communication constraint. Analytical results of periodic sensing efficiency are then deduced while sensing parameters are optimized. Based on these, a recursive sensing algorithm exploiting prior channel state information is developed. Numerical results are presented to demonstrate the potential of our scheme.     

流星余迹系统信道在星状拓扑结构下的设计优化

传统星状拓扑结构的流星余迹通信网络主站与从站采用相同的定速率定功率传输机制。综合星状拓扑网络结构特点与流星余迹信道的特性,本文在考虑传输延时,限带宽等实际因素下分别提出主站与从站不同的传输机制来优化性能。适合相对高数据吞吐量的主站的限带宽变速率传输机制使主站传输效率与定速率传输相比上升了450%;适合对耗能要求敏感的从站的变功率传输机制,在不降低其定速率传输能力的基础上节省55%的发射能量。本文还给出了主从站在指数衰减的流星信道模型下的仿真结果。     

Retracted: State estimation of Takagi-Sugeno fuzzy system in networked control system with stochastic time delays under unknown attacks

This article concerns the event-triggered fuzzy filter design for Takagi-Sugeno (T-S) fuzzy systems subject to deception attacks under the stochastic multiple time-varying delays. A sequence of random variables, which are mutually independent but obey the Bernoulli distribution, is introduced to account for the randomly occurring communication delays. In order to efficiently utilize limited network communication bandwidth resources, the event-triggering scheme is adopted. A fuzzy filter with the attacked input signal is presented. Moreover, due to communication delays caused by event-triggering schemes and transmission, the filter adopts non-synchronous premise variables with the system. Then, by utilizing a model transformation technique, the fuzzy systems are developed. Furthermore, using the piecewise Lyapunov functional method technique, the resulting criterion provides sufficient conditions to ensure that fuzzy systems under deception attacks are stochastically stable with an H_∞ performance. Accordingly, the conditions for the co-design of the fuzzy filter and event-triggering schemes are given. Finally, numerical simulation with the industrial process provided to verify the proposed event-triggered design.     

Biomechanical and perceptual constraints on the bandwidth requirements of sign language

Access to telecommunication systems by deaf users of sign language can be greatly enhanced with the incorporation of video conferencing in addition to text-based adaptations. However, the communication channel bandwidth is often challenged by the spatial requirements to represent the image in each frame and temporal demands to preserve the movement trajectory with a sufficiently high frame rate. Effective systems must balance the portion of a limited channel bandwidth devoted to the quality of the individual frames and the frame rate in order to meet their intended needs. Conventional video conferencing technology generally addresses the limitations of channel capacity by drastically reducing the frame rate, while preserving image quality. This produces a jerky image that disturbs the trajectories of the hands and arms, which are essential in sign language. In contrast, a sign language communication system must provide a frame rate that is capable of representing the kinematic bandwidth of human movement. Prototype sign language communication systems often attempt to maintain a high frame rate by reducing the quality of the image with lossy spatial compression. Unfortunately, this still requires a combined spatial and temporal data rate, which exceeds the limited channel of residential and wireless telephony. While spatial compression techniques have been effective in reducing the data, there has been no comparable compression of sign language in the temporal domain. Even modest reductions in the frame rate introduce perceptually disturbing flicker that decreases intelligibility. This paper introduces a method through which temporal compression on the order of 5 : 1 can be achieved. This is accomplished by decoupling the biomechanical or kinematic bandwidth necessary to represent continuous movements in sign language from the perceptually determined critical flicker frequency.     

A brief discussion of abbreviations [From the Editor]

Abbreviations are a wonderful invention. They help us to say a lot in a very little space. This was very important in the early development of wireless communication, where Morse code was the radio operator's character set. Long words and phrases required relatively long periods of time to be transmitted using this rather slow, narrow bandwidth communications method. To try to correct this problem, radio operators devised and borrowed from telegraph operators standard abbreviations such as the Q code to represent common phrases. For example, QTH referred to the radio operator's location, QRM was radio interference, and QSL meant please acknowledge receipt of this message.     

宽带电力线载波点对点通信性能测试平台设计

在Q/GDW 1379.4-2013通信单元检验技术规范的要求下,为测试低压宽带电力线载波通信单元的工作频段、载波信号发射功率谱密度、抗衰减能力、抗噪声干扰和抗阻抗变化等基本通信性能,给电网公司建设宽带电力载波远程集抄系统提供数据参考和方案依据。根据宽带电力线载波技术的特点搭建了点对点通信性能测试平台。该平台采用三级级联双SMA电源滤波组合,可有效隔离电网谐波、脉冲信号及电力线背景噪声对宽带载波通信单元性能的影响,使测试平台能够充分模拟低压电力线通道,还原现场集抄台区的运行状况,评估载波通信单元的实际可用性。试验数据证明:所建点对点通信性能测试平台试验环境纯净,对2MHz~30MHz通带内的信号衰减达93 d B,可确保宽带载波通信产品测试结果的稳定可靠。     

基于ATM E1的网络远动通道组建

为了适应电力调度自动化信息量不断增多的需求,网络远动通道应运而生,并且使用越来越广泛。文章就江苏农村电力信息网建设中的通信问题,针对美国思科公司Cisco 8500系列设备光纤通信的异步传输(ATM)模式,提出了利用ATM E1电路进行改造,以实现变电站网络远动信息传输功能,文章从网络通道构成、接口转换、E1电路软件配置和通道测试等方面作了深刻的阐述。农村信息网建设当初,设备没有配置以太网接口板,现有的E1端口不能直接与网络设备相连。通过实践证明,使用网桥将带宽为2．048Mbps的E1接口转换成10Mbps以太网接口,实现变电站远动信息的传输,是完全可行的。从而节省了以太网接口板的巨额投资,效果很好,实用性强。     

智能电网调度控制系统主备同道信息对比技术分析

为提高智能电网调度控制系统前置通信的可靠性与数据通道的冗余度,采用双远动装置分别接入双平面的调度数据网,即采用主备通道进行信息传输,这样就存在调控主站多通道接收的值及接收的频度不尽相同的可能。提出了一种智能电网调度控制系统多通道信息智能比对方法,通过网络监听方式获取主厂站信息交互通信报文,利用智能比对算法对遥信、遥测、事件顺序记录（sequence of event,SOE）、遥控、遥调等通信规约参数进行比对,根据比对结果及时输出告警事件。智能电网调度控制系统多通道信息智能比对技术是实现主厂站通道通信质量监测的有效手段,通过该技术可及时发现通道的异常,大大提高了调度自动化系统运行的效率。     

基于几何随机的非平稳车载信道建模及相关性分析

车载(V2V)通信系统是未来智能交通系统的重要组成部分,其非平稳特性已经在信道测量中得到验证。针对V2V多入多出通信系统,提出一种非平稳双环几何随机信道模型。为了描述信道的非平稳性,将到达角(AOAs)和离开角(AODs)的时变特性引入模型中,推导了模型的空间互相关函数(CCF)和时间自相关函数(ACF)等时变统计特征。此外基于修正等面积法(MMEA),开发了相应的仿真模型,研究了散射环境、移动端的移动状态以及天线偏角对信道统计特性和非平稳性的影响。仿真结果表明,所提模型可以有效模拟V2V信道非平稳性,平稳状态下信道的统计特性与平稳双环模型的统计特性具有一致性,验证了本模型的正确性。     

星间通信中带宽和功率联合分配算法

针对星间通信链路的资源分配与现实中业务需求和信道条件不能匹配,导致有限的星上资源不能得到充分利用的情况,本文通过构建星间通信系统容量模型,提出了一种星间通信中带宽和功率协调分配算法。算法根据不同链路具有不同信道条件和业务需求,采用拉格朗日对偶理论和次梯度法,通过对功率和带宽的二次迭代,最终的到功率和带宽的最优解。仿真结果表明本算法能够有效地为不同链路分配合理的带宽和功率资源,使系统总容量得到明显的增加,并对系统资源利用率进行显著的提高。     

Multipath characterization of indoor power-line networks

The time- and frequency-varying behavior of an indoor power-line network is the result of variable impedance loads connected to its termination points. In fact, any signal transmitted through such a communications network is subject to time-varying multipath fading. In this paper, an analytical calculation method is presented, which can be used to determine the multipath components of any point-to-point channel in the indoor power-line environment. The method calculates all transmission characteristics of the network and, therefore, it can be exploited in the process of designing proper transmission algorithms for optimizing system performance. The proposed method is applied to an example network to demonstrate its usefulness in explaining the network's time-dependent behavior and in estimating channel parameters, such as subchannel bandwidth, multipath delay spread, fading conditions, etc.     

Adaptive H∞ event-triggered load frequency control in islanded microgirds with limited spinning reserve constraints

Using an islanded microgrid (MG) with large-scale integration of renewable energy is the most popular way of solving the reliable power supply problem for remote areas and critical electrical users. However, compared with traditional power systems, the limited spinning reserves and network communication bandwidth may cause weak frequency stability in the presence of stochastic renewable active outputs and load demand fuctuations. In this paper, an adaptive event-triggered control (ETC) strategy for a load frequency control (LFC) system in an islanded MG is proposed. First, a bounded adaptive event-triggered communication scheme is designed. This not only saves on network resources, but also ensures that the control center has a sensitive monitoring ability for the MG operating status when the frequency deviations have been efectively damped. Secondly, by fully considering the spinning reserve constraints and uncertain communication delays, the LFC system is described as a nonlinear model with saturation terms. Design criteria for ETC parameters are strictly deduced based on Lyapunov stability theory. Finally, an ETC parameter optimization algorithm based on random direction search is developed to reconcile the bandwidth occupancy and control performance. The efectiveness of the proposed method is verifed in an MG test system.     

无线紫外光与射频混合链路中继协作方案性能分析

将无线紫外光通信与传统射频通信进行优势互补结合,针对双链路异构组网时的中继协作混合传输问题,采用建模与数值计算分析的方法,对比分析了不同策略和参数条件下系统的中断概率和误码率性能。基于无线紫外非直视散射信道和射频无线衰落信道的各自特点,建立了描述双链路并行传输中继与协作问题的模型,给出了3种典型情况下的传输策略。通过理论分析和数值计算的方法,给出了不同策略下混合链路中继的中断概率和误码率表达式,并在不同信道参数条件下对系统性能进行了对比分析。研究结果表明,相比于无线紫外光单链路传输,混合链路的中继协作策略在不同距离和不同参量条件下获得更低的系统中断概率。在误码率为1×10^-6条件下,双链路中继传输可以在不同湍流强度和不同莱斯因子情况下可获得约0.4～6.1 dB的信噪比增益改善。     

继电保护与通信专业的技术配合问题探析

电力通信和继电保护专业之间存在着技术鸿沟,但又密不可分。为了使2个专业密切结合,文章通过对传输220 kV线路继电保护业务通信通道的3个典型故障案例的现场试验分析,说明了造成两项技术难以配合的直接原因,阐述了继电保护、电力通信以及高压检修专业互相配合的重要性,指出只有增进技术层面的相互了解、协调配合一致,才能确保电力系统继电保护信号安全可靠地传输。     

变电站信息数字化综合传输方案

阐述了采用IP技术实现变电站的遥测、遥信、遥控、遥调、遥视、远程诊断维护、故障录波等信息综合数字化传输的原则、技术条件和实现方法。指出其中的关键技术问题是如何分配各类信息的传输带宽和如何控制信息的传输流量,给出了一种优先保证实时性强的信息传输的带宽分配方法和一种通过控制发送方各类信息的传输速率来控制传输流量的方法。在通信软件的编制方法上,提出了通信软接口的概念。将通信软件分为2个层次：IP传送层和协议编解码层,有利于传输协议的标准化。所提出的方法经E1通信测试可以满足各类数据实时性的要求,其结论同样适合于基于IP技术的宽带数据传输。     

IEC60870-5传输规约的应用及试验

讨论了变电站与控制中心的通信信息和传输特点,分析了变电站内远动、继电保护、故障录波、安全自动、环境监控及生产等装置的信息内容和传输要求以及生产控制信息的传输现状,指出IEC60870-5系列传输规约的101为基本远动任务配套标准,102为满足电量计费系统的传输,103为继电保护信息的需要。提出对于大型变电站与控制中心间较复杂的数据信息传输,利用网络允许多协议同时并存和较高的传输速率及容量的特性,以一个网络化的数据传输通道同时采用IEC60870-5系列的4个配套标准(101、102、103、104)传输信息;在较小的变电站,用1 200～9 600 bit/s速率的串行通道,在扩展配套标准IEC60870-5-101引入同用分类服务,实现远动、保护等信息同时传输的方案。指出应用中信息传输时间、对多运行状态对象的控制、继电保护定值的传输、传输厂站信息文档等为尚需解决的问题。     

智能电网用电信息采集系统通信技术应用分析

文章通过对用电信息采集系统业务需求、系统业务架构及系统业务流程进行分析,明确了通信信道层在用电信息系统中的重要作用,介绍了集中器到用电信息系统平台的远程通信技术及采集器到集中器的本地通信技术,并对远程通信技术和本地通信技术分别进行了分析比较,即明确各种通信技术的优缺点后可因地制宜地选择合适的通信方案,可为用电信息通信系统建设提供参考。     

基于MSTP的EOS传输通道性能测试

随着光纤通信技术的发展,越来越多的企业开始在MSTP上利用EOS技术组建本企业的信息网。此举在为数据通信提供便捷的同时,也随之带来该传输网的带宽分配、协议封装以及如何衡量和评价传输电路对数据业务的影响等问题。文章以湖南电力信息广域网为测试背景,根据不同数据封装协议和带宽分配方案,讨论了一种EOS传输通道的性能测试方法,定性地分析了EOS传输电路对所提供数据通信业务的影响,为今后带宽分配决策和数据封装协议的选择提供了理论依据。