Power-Line Communication Channel Model for Interconnected Networks—Part II: Multiconductor System

In this paper, we present an approach to determine the transfer function for multiconductor power-line networks with distributed branches and load terminations for broadband power-line communication (BPLC) applications. The applicability of the proposed channel model is verified numerically in time domain using the finite-difference-time domain (FDTD) method for the solution of transmission lines. The channel model simulation results are in excellent agreement with the corresponding FDTD results. The model therefore could be useful in the analysis and design of BPLC systems involving multiconductor power-line topology.      

Channel Model for Broadband Power-Line Communication

This paper presents a novel approach to model the transfer function of a power-line network. The channel frequency responses of a single-phase power-line channel with interconnections are derived considering different loading at different branches. The model is verified using Alternative Transients Program-Electromagnetic Transients Program (ATP-EMTP). The model simulation results are comparable to ATP-EMTP results. Therefore, the modeling can be considered as a procedure to characterize the power-line channel     

Indoor Power-Line Communications Channel Characterization Up to 100 MHz—Part I: One-Parameter Deterministic Model

Advanced communication technologies have allowed the power-line-communication (PLC) channel to be a transmission medium that enables the transfer of high-speed digital data over the classical indoor electrical wires. The development of PLC systems for Internet, voice, and data services requires measurement-based models of the transfer characteristics of the mains network suitable for performance analysis by simulation. This paper presents a deterministic model describing the magnitude and phase of complex transfer functions of power-line networks using only one parameter. First, a PLC channel classification is realized, and an average magnitude and phase channel model by class is proposed. Second, the multipath characteristic of PLC channels is introduced. A statistical-based channel magnitude generator is built, and a group delay-based phase model is suggested.     

Indoor Power-Line Communications Channel Characterization up to 100 MHz—Part II: Time-Frequency Analysis

Estimations of coherence bandwidth and time-delay parameters from wideband channel sounding measurements made in the 30 kHz-100 MHz band in several indoor environments are described in and taken back in this paper. Powerline communications (PLC) modems rather see a channel which starts almost from 2 MHz . A comparison between coherence bandwidth and time-delay parameters estimated in both frequency bands 30 kHz-100 MHz and 2 MHz-100 MHz is elaborated in this paper. Results are intended for applications in high-capacity indoor power-line networks. The investigation is aimed to show that the PLC channel studies in a band starting from a frequency lower than 2 MHz distorts the real values that an implementer should take, as the PLC modem see only the frequencies from 2 MHz. The coherence bandwidth and the time delay parameters are estimated from measurements of the complex transfer functions of the PLC channels. For the 30 kHz-100 MHz frequency band, the 90 th percentile of the estimated coherence bandwidth at 0.9 correlation level stay above 65.5 kHz and below 691.5 kHz. It was observed to have a minimum value of 32.5 kHz. The maximum excess delay spread results show that 80% of the channels exhibit values between 0.6 s and 6.45 s. And a mean rms delay spread of 0.413 s is obtained. The passage to the 2 MHz-100 MHz frequency band induced an increase of the coherence bandwidth, whose min value is brought back to 43.5 kHz, and an important reduction of the time delay parameters: The min, max, mean, and standard deviation values of the maximum excess delay are almost divided by 2. For the twice frequency bands, this paper studies, also, the variability of the coherence bandwidth and time-delay spread parameters with the channel class , and thus with the location of the receiver with respect to the transmitter, and finally relates the rms delay spread to the coherence bandwidth.     

A Medium-Voltage Cables Model for Power-Line Communication

The aim of this paper is the development of a theoretical model of medium-voltage (MV) cables in the frequency range of 25–200 kHz, which can be easily implemented in the Simulink enviroment. Two transmission-line configurations: 1) line-ground and 2) line-line were considered. The model requires the knowledge of the transmission channel parameters in the frequency domain. Thus, a characterization of MV cables in the two transmission-line configurations by means of experimental measurements was performed on commonly used MV cables, RG7H1R, of different sections, 95 mm$^{2}$ and 185 mm$^{2}$ with an aluminum core and copper shielded. To validate the model, a comparison between the attenuation constant $alpha$ measured and the one simulated for both configurations under study was carried out.      

An Experimental Validation for Broadband Power-Line Communication (BPLC) Model

Recently, different models have been proposed for analyzing the broadband power-line communication (BPLC) systems based on transmission-line (TL) theory. In this paper, we make an attempt to validate one such BPLC model with laboratory experiments by comparing the channel transfer functions. A good agreement between the BPLC model based on TL theory and experiments are found for channel frequencies up to about 100 MHz. This work with controlled experiments for appropriate validation could motivate the application and extension of TL theory-based BPLC models for the analysis of either indoor or low-voltage or medium-voltage channels.     

Modeling and Protection of Hexagonal Phase-Shifting Transformers—Part I: Short-Circuit Model

Owing to several advantages over traditional phase shifters, applications of hexagonal phase-shifting transformers (PSTs) keep expanding. These transformers are built with unique connections of their windings, neither delta nor wye. Short-circuit modeling and analysis methods are not yet fully established for hexagonal phase shifters. This work is divided into two parts. In this part, a digital model of a hexagonal PST is developed and validated. This original material is of assistance when performing short-circuit system studies, relay setting calculations, as well as when modeling internal faults and developing protection techniques for the transformer itself. This paper explains construction of hexagonal PSTs, deriving their sequence impedances under varying taps and compares the model with manufacturer test data and a physical made-to-scale model developed specifically for this study. The transient model introduced in this paper can easily be integrated into the commonly used Alternate Transients Program and real-time digital simulator modeling environments. Part II of this work presents original protection methods for hexagonal PSTs.     

Forecasting-Aided State Estimation—Part I: Panorama

The art of estimating future values of a random process, based upon previously observed or estimated values, is usually known as a priori estimation, prediction, or forecasting. Power system state estimation process can be enhanced if state/measurement forecasts are incorporated into it. Important research efforts have been made in this direction bringing a fresh perspective to the state estimation problem. This paper (Part I) presents a comprehensive survey of forecasting-aided state estimators. It gathers up-covering a period of three decades-research results on the main benefits achieved by state estimators with forecasting capability regarding: data redundancy, innovation analysis, observability, filtering, bad data, and network configuration and parameter error processing. Aspects of modeling, forecasting techniques, and computational effort are also addressed. The second of this two-paper series presents the results of the implementation of a forecasting-aided state estimator in the energy management system of the LIGHT Services of Electricity, a company which provides electric energy to Rio de Janeiro, Brazil.     

多用户电力线通信自适应OFDM系统中的资源分配与交换优化

自适应正交频分复用(OFDM)是一种实现电力线多用户高速数据通信的技术,资源动态分配是这一技术的重要组成部分。文章针对电力线通信的限制条件,探讨了在最大总功率、各用户要求最小速率、各子载波分配最大功率和比特数的约束下,多用户在多子载波上自适应比特和功率分配的数学模型,提出一种新的速率自适应动态资源分配算法,其实现分为4个相互联系的阶段,依次是确定工作子载波、单用户资源分配、子载波和功率交换、比特交换和功率调整。在典型电力线信道环境下的仿真结果表明,该算法比已有的多用户频谱分配优化算法性能更优,能更好地满足多用户资源分配模型的目标要求。     

适用于低压电力线通信的BP译码优化方法

为提高低压配网电力线信道中的信息传输效率,提出一种优化BP译码的改进4折线算法。通过变换化简置信传播(belief propagation,BP)算法的校验节点信息更新函数,建立分段线性函数,并设计误差修正表对不同分段区间进行补偿,利用查表方法实现误差修正值,可降低解码实现复杂度。在Middleton A类电力线信道模型下的仿真结果表明,经分段线性函数优化后的译码算法与BP算法的误码率(bit error rate,BER)性能相近,而译码的复杂度却大大降低,有利于算法的软硬件实现,为电力线载波通信提供了一种高性能的信道编码方案。     

智能电网电力线通信系统信道噪声模型分析

将智能电网电力线通信系统作为研究对象,以建立两种噪声模型之间的关系、比较两种模型下的信噪比SNR(signal-to-noise ratio)为研究目标,提出两种噪声模型来模拟电力线通信信道中噪声情况的方法。该方法利用循环平稳噪声模型和米特尔顿A类噪声模型的概率密度函数,得出电力线通信信道中的噪声类别。同时,通过数学推导,得出两种噪声模型在正交频分复用OFDM(orthogonal frequency division multiplexing)系统中SNR表达式和在正交幅度调制16 QAM (quadrature amplitude modulation)技术下比较两种噪声模型的SNR。最后,利用MATLAB软件系统仿真,仿真结果显示,循环平稳噪声模型比米特尔顿A类噪声模型的SNR高2.5 dB左右,智能电网电力线通信系统可靠性得到提升,为电力线通信的发展研究提供了一定的理论基础。     

分布式天线系统信道选择策略

分布式天线系统的信道分配问题是整个系统发挥优势的关键之一,考虑选择四根天线的情况,采用动态信道分配方案,对于随机、最大SIR、最小SIR和最大SIR最小等方案进行仿真分析,最小SIR由于使得信道分配达到最大紧致,阻塞率最低,充分利用频谱资源.     

发输电互联等值系统风险评估的解析模型

为快速而精确得出发输电组合系统中区域元件参数变化后的系统风险指标,在发输电互联系统改进等值模型的基础上,推导出系统风险指标对区域元件参数变化的解析表达式,并提出系统风险评估的算法和流程。利用该解析表达式所得出的图表不但可直观反映元件各参数变化对系统风险指标的影响,还可为电力系统规划和效益评估提供指导意见。论文还以互联RBTS系统和IEEE-RTS96系统为例,通过故障重数对系统风险指标影响的定量化研究,解释和证明了高阶故障对大电力系统风险评估的重要性。     

互联电力系统可靠性评估的改进等效模型

深入研究了互联组合发输电系统可靠性评估的等效问题。对外部系统提出了包括等效发电机、等效输电线、等效负荷在内的改进等效模型,利用外部系统停运负荷的概念改进了参数的计算,并以网络流法建立参数的计算流程。基于不分担电力不足协议提出一种新的等效状态合并方法,以便进行互联系统可靠性的评估,得出结论:①等效输电容量参数的加入及参数计算方法的改进,可以更加准确地反映被等效外部系统的风险水平;②等效状态合并的新方法既可保证精度又能显著提高计算速度。采用本文方法对RBTS可靠性测试系统进行评估,结果验证了该方法正确可行。     

Reliability of SiGe HBTs for Power Amplifiers—Part I: Large-Signal RF Performance and Operating Limits

This paper examines the performance and reliability implications associated with aggressively biased cascode SiGe HBT power-amplifier cores under large-signal RF operating conditions. The role of high-power RF stress on device degradation and failure is examined in detail. General expressions for a large-signal RF safe-operating area, which account for the effect of load impedance on the dynamic output current and voltage characteristics, are presented. These show excellent agreement with experimental results. Useful operating guidelines for reliable large-signal operation are provided.      

Expressions for Current/Voltage Distribution in Broadband Power-Line Communication Networks Involving Branches

Estimation of electromagnetic (EM)-fleld emissions from broadband power-line communication systems (BPLC) is necessary, because at its operating frequencies, the radiated emissions from BPLC systems act as sources of interference/crosstalk to other radio-communication systems. Currently, the transmission-line (TL) system used for BPLC is complex, involving arbitrarily/irregularly distributed branched networks, arbitrary termination loads, varying line lengths, and line characteristic impedance. In order to study the electromagnetic-compatibility (EMC) issues associated with the radiated emissions of such complex BPLC networks, knowledge of current and voltage distributions along the length of the power-line channels is needed. This paper attempts to derive and present generalized expressions for either the current or voltage distribution along the line (whose TL parameters are known) between the transmitting and receiving ends for any line boundary condition and configuration based on the TL theory. The expressions presented in this paper could be beneficial for direct calculation of EM emissions from BPLC systems.     

Pantograph Arcing in Electrified Railways—Mechanism and Influence of Various Parameters—Part I: With DC Traction Power Supply

Pantograph arcing is a common phenomenon in electrified railway systems. This is also a source of broadband-conducted and radiated electromagnetic interference (EMI) for vehicle as well as traction power and signaling systems. In this paper and the companion paper, experimental analyses of pantograph arcing phenomena are presented for dc and ac feeding systems, respectively. Influences of different parameters on dc traction system, such as supply-voltage polarity, relative motion between pantograph and overhead contact wire, namely, forward motion along the track (longitudinal), and lateral sliding motion of the pantograph (zigzag) are presented here. From the voltage and current waveforms of the test runs, it is shown that pantograph arcing is a polarity-dependent phenomenon. For the positive-fed overhead traction system, where pantograph is cathode, the supply interruptions due to zigzag motion are comparatively less compared to negatively fed traction systems. As a result, the transients, due to pantograph arcing, are more frequent in negatively fed traction systems. It is found that the arc root movement along the electrode surfaces (pantograph-contact wire) is governed by the relative motion and polarity of the electrodes. The analyses presented in this paper also form a foundation to understand the pantograph arcing process and the corresponding influential parameters with the ac supply presented in the companion paper. The findings presented in this paper could be beneficial for coming up with appropriate mitigation techniques from the EMI due to pantograph arcing in dc-fed traction systems.     

面向配电自动化的中压电力线高速数据通信终端设计

论述了以中压(10kV)配电网为信道、面向配电自动化应用的高速数据通信系统的整体解决方案,详细介绍了该系统的终端设计.提出将低压电力线通信中成熟运用的数据调制/解调及组帧技术移植到中压环境的思想,并针对中压电力线因过长链路易造成信号严重衰减的问题,在终端设计中采用基于Weinberg滤波电路和传输线变压器耦合的匹配策略解决高频宽带(4～22MHz)信号的功率放大.实现了信号安全、可靠地向中压电力线的注入,可满足10km左右的传输要求.     

Forecasting-Aided State Estimation—Part II: Implementation

This paper is the second part of a two-part paper addressing power system forecasting-aided state estimation. Part I presented a comprehensive survey on the subject, including future prospects. Part II is devoted to presentation and discussion of numerical results obtained with the implementation of a forecasting-aided state estimator in the energy management system of LIGHT Services of Electricity, which is company that supplies Rio de Janeiro, Brazil. This estimator is submitted to different situations, such as: normal operating conditions, presence of spurious measurements (including those which are critical), and occurrence of unpredictable sudden changes in the state of the LIGHT system.     

On the Efficacy of Using Ground Return in the Broadband Power-Line Communications—A Transmission-Line Analysis

The power-line infrastructure has been identified as an efficient system suitable for broadband power-line communication (BPLC) to connect and control various end users. However, the network is affected by stochastic attenuations due to the number of interconnected branches, their line lengths, associated terminal loads, etc. There is yet another parameter that could influence the above stated attenuations or distortions depending on the way the signals are allowed to return to the transmitting end. In this paper, we investigate whether a finitely conducting ground return could be used for BPLC and to investigate its performance over the conventional methods where one of the adjacent power-line conductors is used as signal return. This study could be helpful to those who are proposing the use of ground as a return conductor in BPLC systems. It will be shown that the use of ground return for the BPLC system is effective or better only when the ground conductivity is high (>50 mS/m). When ground conditions are poorer, attenuations increase with frequency, making them unsuitable for BPLC. There are situations where poor ground conditions can still be used but only the transmission-line lengths are shorter. The analysis presented here is based on transmission-line solutions both under lossless (without ground return) and lossy (with ground return) conditions and are applied to typical low-voltage and medium-voltage channels. Comparisons are also made based on the power spectral densities and channel capacities.