考虑直流控制系统影响的HVDC输电线路后备保护研究

在考虑直流控制系统影响的情况下,详细分析了HVDC输电线路区内、区外的故障特征以及直流控制系统的动作特性和控制状态。引入并分析了基于开关函数的交直流系统二次谐波计算等值模型。通过分析故障期间换流器触发角和直流侧二次谐波量的变化特征,提出了一种新的以换流器触发角为保护动作量,利用二次谐波分量闭锁的直流线路后备保护方案,给出了保护整定的理论计算方法。与直流线路纵联差动保护相比,该保护不因直流电流波动影响而被闭锁,保护动作时间较快;与微分欠压保护相比,具有更高的抗过渡电阻能力。通过PSCAD/EMTDC大量仿真计算,验证了该保护能可靠区分直流线路区内、区外故障,与直流线路纵联差动保护和微分欠压保护相比具有明显的优越性。     

Femtosecond optical parametric amplification with dispersion precompensation

In this paper, we study a midinfrared femtosecond optical parametric amplifier (OPA) that is severely affected by group velocity dispersion (GVD). Both theoretical and experimental results show that GVDs in nonlinear crystals will significantly degrade the performance of a femtosecond OPA. By introducing a prechirp to the pump pulse, the effect of GVD can be effectively compensated. A lithium-niobate-crystal-based femtosecond OPA demonstrates that the conversion efficiency with optimally prechirped pumping is nearly twice that of the nonchirp case, and the output pulses can be further compressed to nearly their Fourier-transform limit by prism pairs.     

政平换流站的无功功率控制

龙泉-政平±500kV直流输电系统自2003年6月正式投运,起着联系华中和华东两大区域电网的重要作用,研究其无功功率控制软件RPC的功能、结构和控制方法对其安全可靠运行和其他直流输电工程建设有着重要意义。为此介绍了政平换流站绝对最少滤波器等控制功能的控制模式。并简要说明了该站无功功率控制系统运行情况,指出需注意的问题以供同行业参考。     

一种新型的高精度Sigma_Delta调制器结构

为实现低失真高动态范围的模数转换,提出了一种新型高精度Sigma_Delta调制器系统。首先,设计了一种新型的二阶单环一位量化结构,结构中增加两支前馈路径,并调整了核心积分器和信号加算模块的逻辑关系。同时,为实现量化噪声的二阶整形以及输入信号的无延迟传输,进一步适配和改进了积分器的传输函数。最终,所提出的调制器实现了更高的信噪比和更宽的动态输出范围。基于Matlab 的系统级仿真结果表明,在信号带宽1KHz、采样信号频率1024KHz的条件下,所提出调制器的信噪比为106.6dB,有效位数为17.41bit,二次谐波失真为-82.7dB,动态范围为104.76dB,整体指标性能良好,为高阶MASH结构Sigma Delta调制器的研发提供了新方向。     

基于二次谐波环流注入方法的混合MMC电容电压平衡控制策略

当高压直流输电系统直流侧电压降低时,混合模块化多电平变换器(MMC)将工作在过调制状态,面临电容电压不平衡的问题.分析过调制状态下混合MMC中半桥与全桥子模块电容充放电过程与能量变化,提出一种简化的二次谐波环流参考幅值的生成方法.采用二次谐波环流注入方法避免混合MMC中半桥与全桥子模块电容电压不平衡的发生,实现半桥与全桥子模块电容在一个周期内的充放电平衡,使混合MMC在直流电压降低时继续传输有功功率.仿真与实验结果表明,所提出的二次谐波环流注入方法能够有效实现混合MMC在过调制状态下的电容电压平衡.     

换相电压负序分量对LCC-HVDC输电系统换相的影响分析及其抑制策略

针对逆变侧交流系统故障下传统的基于电网换相换流器的高压直流(LCC-HVDC)输电系统容易发生换相失败这一问题,推导了换相电压负序分量与锁相环的定量关系,并定性分析了换相电压负序分量对LCC-HVDC输电系统换相的影响.在此基础上提出了一种改进双二阶广义积分器锁相环以抑制多次换相失败.该锁相环首先采用具有分离特性的相序...     

Application of SPICE simulation to study WDM and SCM systems using EDFAs with chirping

The authors have proposed an equivalent electrical circuit model of erbium-doped fiber amplifiers (EDFAs), including the chirping effect for teaching or studying the distortions and performance of lightwave transmission systems. Through the aid of a SPICE circuit simulator, its validity is demonstrated by analyzing the cross modulations of an eight-channel wavelength division multiplexing system. The intermodulations in an amplitude modulation-subcarrier multiplexing (SCM) system are demonstrated. The channel-number dependence of the composite second-order distortion in a 42-channel SCM system is shown, and its applications to analyze other systems are also discussed.     

面向人体通信的皮层脑电信号传输特性研究

随着人体通信的发展,对于人体脑电信号的研究和应用越来越广。现有研究局限于非侵入式脑电信号,对侵入式皮层脑电信号的研究较少。研究采用时域有限差分方法建立人体模型,探讨侵入式皮层脑电信号的传输特性。首先,分析10 MHz～10 GHz高频载波频段内不同接收电极间隔下信道传输增益的变化,确定皮层脑电信号最优载波传输频段。通过SAR量化分析人体吸收的电磁能量,评估模型的安全性。其次,研究发射器和接收器在不同距离下的路径损耗和阴影效应,建立了通信距离与路径损耗之间的二阶指数模型。结果表明,载波频段在约1 600 MHz左右,且接收器两电极间隔为10 mm时,信道传输增益达到最大值-45.63 dB。在信号传输过程中,通信距离和路径损耗之间遵循二阶指数模型关系,最终建立的路径损耗模型符合二阶指数分布,更能准确地描述信道的传输特性。     

PAT: a power analysis toolbox for MATLAB/Simulink

A power system simulation environment in MATLAB/Simulink is presented in this paper. The developed power analysis toolbox (PAT) is a very flexible and modular tool for load flow, transient, and small-signal analysis of electric power systems. Standard power system component models and a wide range of flexible AC transmission systems (FACTS) devices are included. Its data structure and block library have been tested to confirm its applicability to small-to-medium-sized power systems. Its advantages over an existing commercial package are given.     

An accurate voltage solution method for radial distribution systems

This paper formulates a set of equations (SOE) to describe a radial distribution system with high R/X ratio. The SOE comprises 3(N ? 1) second-order equations and an equal number of variables for an N-bus system. The proposed method solves this SOE using the first-order Newton-Raphson technique. The SOE model accounts for elements such as transformers, transmission lines, shunt capacitors, constant PQ loads, and constant impedance loads. Irrespective of the R/X ratio values of the lines in the system, the SOE preserves a strong diagonal characteristic. As well, this SOE is devoid of bus phase angles, unlike the 2(N ? 1) ac power flow equations used to describe transmission systems. The proposed method is compared with other methods reported in the literature for distribution systems, such as Newton-based methods and recursive methodologies that use forward and reverse sweeps. Tests conducted on radial distribution systems with 43, 69, and 5002 buses show the new method to be more accurate than other methods reported in the literature.     

Model Predictive Control Based Ramp Minimization in Active Distribution Network Using Energy Storage Systems

The growing integration of renewable energy sources, especially the residential photovoltaic (PV) systems, in the distribution networks (DNs) aggravates the ramp-events in transmission system. To address this issue, we propose a novel look ahead dispatch model for the ramp minimization in DNs using distributed energy storage systems (ESSs). The dispatch problem considering the scheduling of ESSs is modeled as a finite-horizon optimization problem and is carried out using model predictive control (MPC) method that takes both current and future information into account. In addition, the optimal power flow in DN is formulated as a second-order cone programing problem to guarantee the global optimality. Numerical results on IEEE 37-bus distribution network show that our proposed model not only brings about 74% reduction of maximum ramp but also yields the near-minimum system operating cost.     

含抽蓄电站与新能源发电的柔性直流系统日前优化调度方法

多端柔性高压直流输电技术可实现大规模可再生能源发电的多点汇集送出,通过接入和调控抽水蓄能(以下简称"抽蓄")电站可进一步平抑可再生能源出力波动、匹配负荷侧需求.针对含新能源发电和抽蓄电站的多端柔性直流系统,采用生成场景集方法建立了考虑新能源发电出力不确定性的日前随机优化调度模型.该模型详细考虑了定速与可变速抽蓄机组运行约束和抽蓄电站库容约束,同时包含了计及柔性直流电网有功损耗的潮流约束.通过对柔性直流电网潮流约束二阶锥松弛,将所建立模型转换为以期望运行费用最小为目标的混合整数二阶锥规划问题,可求解获得日前优化调度方案.以中国张北柔性直流示范工程为例进行仿真分析,验证了所提方法的有效性.     

考虑多维应用场景的MMC-MTDC系统拓扑选择和参数配置

针对基于模块化多电平换流器的多端柔性直流 (MMC-MTDC) 输电系统,提出考虑应用场景多维特征的拓扑选择和参数配置方案。根据时间特性、空间分布和资源容量3个维度的场景特征,建立考虑拓扑差异的多端MMC-MTDC输电系统全寿命周期经济性优化模型。提出改进的二阶锥规划(SOCP)松弛方法,将非凸的二次优化转化为SOCP,得出不同应用场景下经济性最优的拓扑结构,制定相应设备出力及线路容量等参数配置方案。参考中国张北柔性直流电网和舟山多端柔性直流输电工程参数,设计对应长、短2种输电距离典型应用场景的四端和五端MMC-MTDC输电系统。从全寿命周期内的总经济效益、新能源消纳率和网损大小3个方面对3种拓扑结构进行经济性分析,验证所提拓扑选型方法的效果。     

二阶拉曼和一阶遥泵组合的超长距技术在特高压工程中的应用

随着特高压输电网工程建设,超长距光纤通信传输技术应用也越来越多,10 Gb/s系统超长距光纤通信传输技术在很多特高压工程中都有应用。根据10 Gb/s传输系统的主要因素分析及国内外超长距光纤通信传输技术应用情况和可用技术,结合南方电网某多端直流工程给出了一段超长距光纤通信的试验电路方案。试验电路利用二阶拉曼和一阶遥泵组合方式的超长距光纤通信传输技术可实现470 km的传输距离,并给出了相应的设备配置方案和软件计算结论,为后续工程建设积累了经验。     

网络视频传输

文中介绍视频点播(VOD)系统的基本框架及TCP/IP的Socket网络编程接口,并给出利用它在网络上进行视频传输的简易点播系统.这对于今后VOD系统的进一步研究有重要意义.     

基于交替方向乘子法的输-配-天然气系统分布式优化调度

随着电力网络与天然气网络耦合程度的加深以及传统配电网向主动配电网的转变,传统输配电气分离下的优化调度无法充分利用各种资源的灵活控制能力,不能获得整体最优解.因此,考虑电气耦合下的输配气协同优化,提出一种输-配-天然气系统优化调度模型.此外,考虑到未来输电系统运营中心、配电系统运营中心与天然气系统运营中心之间的独立性,为了保护各运营中心的信息隐私,提出了一个基于交替方向乘子法的分布式求解框架求解所提模型.为了确保分布式求解算法的收敛性,利用二阶锥松弛方法将气网优化问题转化为凸优化问题.算例结果表明,考虑电气耦合的输配气协同优化能够充分利用主动配电网中的多能耦合资源和储能资源,促进可再生能源消纳,提升系统总体运行经济性.此外,所提分布式求解算法的精确性和收敛性也得到了验证.     

The dynamics of a non-linear discrete oscillator

The dynamic behaviour of a simple second-order discrete system with a single non-linear factor, specified by (x, y)- (Ax + B(y + sin(2π(x +y))), x), (A, B) ? D = {(A, B): A, B ≥ 0, A + B < 1} - is studied. the parameter subspace of D is analysed in detail. the bifurcation sets of the system are found. the existence of chaos in the system is proved by applying Marotto's theorem. the result of computer simulation agrees well with its analytical counterpart, and confirms that the single non-linear factor ? = sin(2π(x + y)) is indeed the crucial point of a very complicated dynamic behaviour, including the alternative emergence of periodic, quasi-periodic and chaotic phenomena, of this simple second-order oscillator.     

An expression of system connection considering transmission delay

This paper presents an expression of system connection considering transmission delay. In a research field of decentralized system or information system, the expression method of the system connection is a very important issue. Therefore, several expression methods of system connection have been proposed so far. However, those expressions are mainly based on binary operations without consideration for the transmission delays on connection paths although the concept of time is very important for expression of system connection. In this paper, expression methods of system connection considering transmission delays on the paths are proposed. Those expressions are based on exponential‐type expression and can express both connections and transmission delays. Furthermore, the expression that can express connections, transmission delays, and past subsystems is also proposed. As one example of the application of proposed expressions, application for path selection of the design of network‐based control system is described. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 45–54, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20839     

分频海上风电系统的技术经济分析

介绍了分频输电系统(FFTS)应用于海上风电的拓扑结构,并通过一个装机容量300 MW、离岸距离250km的算例,比较其与现有高压交流(HVAC)和高压直流(HVDC)并网方式的技术及经济优劣。FFTS通过降低输电频率(如50/3Hz),显著降低交流电缆中的充电电流,提升海底交流输电的效率与性能。结果表明,FFTS能满足算例的并网需求,且风电穿透率大于HVAC。算例中FFTS换流站的投资折算和年维护费用比HVDC少9 126万元,等年值比HVDC低7.28%。在算例的基础上,文中进一步给出了FFTS-HVDC临界经济距离—装机容量曲线,相对而言FFTS更适用于装机容量大、离岸近的风电场,对于300 MW风电场,二者的临界经济距离约为634km,远超已有和规划中的海上风电场的离岸距离。分析结果表明了分频海上风电系统所具有的应用潜力。     

Design,implementation, and test of an SDR for NVIS communications

Although many physical layer solutions have appeared for remote sensors and Internet of things during the recent years, none of them is suited to very remote sensors in areas away from any mobile operator coverage. In that case, a solution on the basis of near vertical incidence skywave (NVIS) with reflection in the ionosphere may be very attractive. Using NVIS, no line of sight is needed and the coverage is much bigger than any other system operating in either the very high frequency (VHF) or ultra high frequency (UHF) band. In this paper, we present a new transmission scheme for very remote sensors using the NVIS transmission technique.