Effective response of nonlinear cylindrical coated composites under external AC and DC electric field

This paper uses the perturbation method to study effective response of nonlinear cylindrical coated composites. Under the external AC and DC electric field Ea （1 ＋sin ωt）, the local potentials of composites at all harmonic frequencies are induced. An effective nonlinear response to composite is given for the cylindrical coated inclusions in the dilute limit.

Research on Total Electric Field for DC Lines Converted from Double-Circuit AC Lines

With rapid growth of power demand, transmission capacity is also in urgent need of upgrading. In some cases, converting existing AC transmission lines to DC lines can Improve the transmission capacity and reduce the construction investment. In this paper, the upstream finite element method was expanded to calculate the total electric field of same tower multi-circuit DC lines converted from double-circuit AC lines, and the validity of the algorithm was confirmed by experiments. Taking a DC line converted from a typical same tower 500 kV double-circuit AC transmission line as an example, the surface electric field and the ground total electric field in different pole conductor arrangement schemes were calculated and analyzed, and the critical height of pole conductors for DC lines in residential and non-residential area were determined. Then, the corridor width of DC and AC lines at critical height in residential and non-residential areas before and after AC-DC line transformation were compared. The results indicate that for DC lines converted from common 500 kV double-circuit AC lines, the ground total electric field can meet the requirements of corresponding standard with appropriate pole conductor arrangement schemes.

Analyzing Electric Circuits with Computer Algebra

This report shows how starting from classic electric circuits embodying commonly electric components we have reached semi-complicated circuits embodying the same components that analyzing the signal characteristics requires a Computer Algebra System. Our approach distinguishes itself from the electrical engineers’ (EE) approach that relies on utilizing commercially available software. Our approach step-by-step shows how Kirchhoff’s rules are applied conducive to the needed circuit information. It is shown for the case at hand the characteristic information is a set of coupled differential equations and that with the help of Mathematica numeric solutions are sought. Our report paves the research road for unlimited creative similar circuits with any degree of complications. Occasionally, by tweaking the circuits we have addressed the “what if” scenarios widening the scope of the investigation. Justification of the accuracy of our analysis for the generalized circuits is cross-checked by arranging the components symmetrizing the circuit leading to an intuitively predictable reasonable result. Mathematica codes are embedded assisting the interested reader in producing and extending our results.

无人机AC/DC电源的小型化设计

介绍了无人机机载AC/DC电源的发展要求,分析该种电源小型化设计的难点所在,运用系统优化设计的方法分析电源的各功能部件。通过采用替换元件、重建结构、集成电路等手段使电源系统保持成本尽可能低的同时做到体积最小。实现了应用的高效率和灵活性,对我军无人机整体性能的进一步提升具有十分重要的意义。

基于优化设计线性矩阵不等式的三相DC-AC变换器鲁棒性跟踪控制

介绍了一种优化设计的鲁棒性控制技术,针对逆变系统中可能存在的不确定性,如滤波电感值,滤波电容值,通过状态反馈和整合跟踪错误,优化设计线性矩阵不等式(LMI),获得状态估计器最佳增益,使收敛速度最大化,在同步dq坐标系中加以描述,采用空间矢量调制技术实施。仿真结果和实验测试证明该优化控制方法具有良好的跟踪性能。

级联多电平高压DC/AC变换器单周控制策略

将单周控制技术用于级联多电平变换器提高其控制性能。在理论分析的基础上,建立了级联多电平DC/AC变换器单周控制模型,并建立了4个3级H桥三相级联多电平电路仿真实例。在开关频率为2 500 Hz、滤波电感为4 mH、滤波电容为14μF、每级H桥直流侧电压为500 V并在10%范围内变化时,变换器输出交流相电压幅值为1 268 V,线电压幅值为2 193 V,输出电压稳定,4个实例的电压THD均小于5%。理论与模拟实例分析表明:单周控制用于级联多电平变换器控制具有控制电路简单、控制效果好、输出稳定等特点。

The effect of blending polypropylene on the electrical properties of polymeric insulation material Hifax

Extensive physical testing has suggested that polymeric material Hifax (Flexible Polypropylene)could be a promising candidate for the next generation of DC insulation. In the work presented in this paper,the DC conductivity and AC breakdown of this polymeric insulation material have been measured as a function of temperature. The results show that Hifax cable insulation has a higher AC breakdown strength than EPR and XLPE (crosslinked polyethylene), and the DC resistivity of Hifax is larger than that of XLPE and oil-impregnated paper insulations. The electrical stress coefficient of resistivity of Hifax wire insulation increases with temperature, which needs to be taken into account in calculating the electrical field distribution across DC cable insulation. It has been observed that there is an anomalous change in resistivity at high electrical field, suggesting charge trapping and detrapping processes are present in Hifax cable insulation. It is concluded that blending Hifax with 62% polypropylene decreases the breakdown strength significantly.

电动汽车车载充电器PFC AC/DC变换器设计

为了减少电动汽车接入电网充电时对电网的谐波污染,同时提高电力利用率,必须进行功率因数(PFC)校正。PFC AC/DC作为车载充电器的核心部分之一,可为后级DC/DC系统提供稳定的直流电压。针对功率等级为2 k W的车载充电器,采用升压(Boost)PFC主拓扑结构和基于平均电流控制的AC/DC变换器设计方案,设计了具有PFC的AC/DC变换器,详细给出了其主电路和控制电路的设计流程,包括器件选型、控制策略选择、主电路及控制电路的参数配置。最后通过系统仿真及样机实验测试,验证了系统动态及静态性能。

运用多目标灰狼优化的航空有源AC/DC变换器研究

针对航空多电发动机传统交直流(AC/DC)变换器在减小体积、质量与抑制谐波之间存在矛盾的问题,提出了将有源电力滤波器(APF)与多边形联结自耦变压整流器(ATRU)相结合的自耦变压有源滤波整流器(ATPFRU)。由于所提新型ATPFRU是一个高度非线性的系统,设计分数阶PI控制器,并以该控制器参数为优化变量,考虑输入电流总谐波损失(THD)和直流侧储能电容电压响应性能的多目标优化问题,基于灰狼优化算法,同时实现了对输入电流谐波的有效抑制和对直流侧储能电容电压的有效控制。仿真结果表明:所提ATPFRU拓扑结构在减小AC/DC变换器体积和质量的同时,有效抑制了输入电流谐波并实现对直流侧储能电容电压的良好控制,获得了满意的多目标优化结果。

Analysis of Non-Sinusoidal Steady Electric Field of ±500 kV Converter Transformer

The line side winding is under the fundamental frequency AC voltage, while the valve side winding contains not only fundamental AC voltage component, but also the DC voltage component, fundamental AC voltage component, and higher harmonic voltage components when the converter transformer is at its normal operating condition, and the electric field of converter transformer is a non-sinusoidal steady one. To analyze the non-sinusoidal steady electric field containing the DC component, fundamental AC and higher harmonic components, the voltage spectrum of the valve winding in a ±500 kV converter transformer is firstly analyzed, and the non-sinusoidal periodic steady electric field is obtained by the fast discrete Fourier transform. Different resistivity of the oil and oil-immersed paper is adopted to simulate the aging of oil paper insulation at operation, and get the non-sinusoidal steady electric field.

Synthesis and Electrical Properties of Polyaniline Composite with Silver Nanoparticles

Polyaniline/silver (PANI/Ag) nanocomposite was prepared by chemical oxidative polymerization of aniline monomer in the presence of nitric acid. The formation of PANI/Ag nanocomposite was characterized by XRD, FTIR, TEM, UV-vis spectroscopy. The XRD patterns indicated that the crystalline phase of Ag is cubic with crystallite size of 93 nm. The TEM image shows that the Ag nanoparticles are well dispersed in the polyaniline matrix. Optical measurements show that the value of optical band gap of nanocomposite is lower than that of pure PANI. The DC-, AC-conductivities, dielectric permittivity (ε') and dielectric loss (ε'') of (PANI/Ag) nanocomposite and pure PANI have been measured in the temperature range from 303 to 723 K and frequency range from 10 to 103 kHz. The electrical conductivity of the (PANI/Ag) nanocomposite is higher than pure PANI. Temperature variation of frequency exponents in this blend suggests that AC-conductivity is attributed to correlated barrier hopping mechanism. At all frequencies, the ε' value for (PANI/Ag) nanocomposite is higher than that for pure one. The higher dielectric constant of the PANI/Ag nanocomposite indicates their better ability to store electric potential energy under the influence of alternative electric field.

Effective AC and DC Responses of Nonlinear Composites at Higher Concentration

For higher concentration of inclusions, an effective medium approximation （EMA） method is used to investigate the bulk effective response of weakly nonlinear composites, which are subject to the constitutive relation of electric displacement and electric field, Dα = εαE ＋Xα｜E｜^2 E. As an example of three dimensions, under the external AC and DC electric fields Eapp = Eα（1 ＋ sinωt）, we have derived the general effective nonh＇near response of composites by the EMA method for higher concentration of spherical inclusions. Furthermore, the effective nonlinear responses at harmonics are predicted.

化害为利提升电功效率的AC／DC模块

节能减排环保理念，已逐渐成为全球人类共识，尽量提升电功效率，是当代电力电子工程师肩负天职之一。文中介绍了从回收有害的THD谐波能量，甚至回收EMC杂波能量，把这些本来有害的“垃圾”能量，化害为利，提升AC／DC效率，是很有现实意义的事。

双绕组感应发电机交直流集成发电系统的自抗扰控制策略

针对双绕组感应发电机交直流集成发电系统,为实现简单易调、性能优越、负载适应力强的发电控制,该文提出一种基于线性自抗扰控制器的交直流电压控制策略,通过交流电压和直流电压与控制绕组和功率绕组的传递函数模型,构建交直流电压的线性扩张状态观测器,同时对交流电压有效值、直流电压和电压扰动进行观测,并利用电压和扰动观测值设计线性误差反馈控制律,对交直流电压进行控制。最后,通过仿真和实验验证该控制策略提高电压扰动抑制能力和负载适应性,同时各模块参数可独立设计、控制器结构简单,避免需要较多传感器及降低调参难度。

海上风电场交流集电和多端柔直输电并网系统多目标优化规划

集电和输电并网系统的优化规划对海上风电场(offshore wind farm,OWF)的投资经济性和运行可靠性有着重要影响。对于OWF中交流集电和多端柔直输电的并网方式,建立了拓扑与潮流耦合的兼顾经济性和可靠性的多目标优化规划模型。模型中利用拓扑冗余度直接近似计算风机停运损失电量,并考虑了新型双边环形的交流集电系统拓扑结构和基于连通性约束的多端柔直输电系统拓扑结构,实现了对集电和输电系统拓扑连接,交流和直流海底电缆类型,海上升压换流站数量、容量、位置,和连接到海上升压换流站馈线数量的协调优化规划。并且,提出了一种直接求解多目标优化问题折中最优解的方法,通过凸化处理将原混合整数非线性规划模型转化为混合整数凸二次规划模型,以高效求解获得最优规划方案。最后,对2个分别含36台和78台风机的实际OWF算例进行分析,验证了所提出模型和方法的正确有效性。

复杂运行条件下非均匀老化油纸绝缘典型电场变化特性

油纸绝缘作为变压器的主要绝缘部分,长期运行后变压器主绝缘发生的非均匀老化现象,在复杂运行条件下(环境温度、受潮情况,电压类型)将导致工况运行时主绝缘内的电场分布发生变化,因此明确工况运行下非均匀老化油纸绝缘内特征位点(最大场强处)电场的变化特性至关重要。通过开展不同老化、受潮程度油纸绝缘材料的介电参数测试,明确了老化后油纸绝缘材料的工频介电常数、直流电导率随着运行条件的变化规律,通过构建基于GA-BP神经网络的老化油纸绝缘材料介电参数模型,实现了非均匀老化油纸绝缘介电参数的多元非线性定量表征;同时考虑油浸纸板老化对油纸间水分平衡规律存在的影响,修正了非均匀老化油纸绝缘内的油纸水分分布,并根据典型非均匀老化主绝缘结构,构建了非均匀老化油纸绝缘典型电场分布模型;最后,考虑到当前特高压电网中,区别于普通交流变压器绝缘所承担的交流电压,换流变压器阀侧绕组承担的电压中含有较高的直流分量,导致其面对的更高的绝缘水平要求。通过分别设定两种外施电压,并在复杂运行条件下,针对不同非均匀老化阶段的油纸绝缘模型的典型电场分布进行仿真计算,揭示了非均匀老化油纸绝缘电场变化特性,明确了实际运行中应加以注意的运行工况,为变压器的运维策略提供了重要的理论支撑。

电力机车DC600V供电系统的改进

为适应“4·18”提速需要,对电力机车DC600V供电系统进行冗余改造,加装车载故障诊断和远程监控系统。新装置统一了列车供电接地方式,提高了可靠性,实现了信息化,改善了维修性能,现场应用证明效果良好。

基于自适应加权预测-校正内点法的含VSC-HVDC电力系统最优潮流

加权预测-校正内点法(WPC-IPM)求解含电压源型高压直流输电(VSC-HVDC)的电力系统最优潮流时,迭代中后期校正环节加权会减慢收敛速度。提出一种自适应加权预测-校正内点法(AWPC-IPM),该方法以对偶间隙的变化趋势作为加权与否的判据,对偶间隙增大时加权,以抑制校正方向错误导致的收敛性变差,对偶间隙减小时不加权,以加快收敛。算例仿真结果表明,所提方法既有效抑制了校正方向错误对预测-校正内点法(PC-IPM)的影响,又加快了迭代后期的收敛速度。

考虑电动汽车和蓄电池联合储能的交直流混合微电网功率协调控制策略

针对电动汽车作为灵活储能分散接入交直流混合微电网后过度依赖双向互联接口变换器进行子网间储能交互的问题,提出一种考虑电动汽车和蓄电池联合储能的交直流混合微电网功率协调控制策略。首先,考虑交、直流子网净功率和功率互济级最大传输功率作为约束条件,将其划分为四种运行状态,并进一步分析功率互济级功率传输方向和储能荷电状态,详细划分不同模式对应的具体工况;然后,考虑电动汽车和蓄电池的响应优先级,设计联合储能动作规则,并详细研究交、直流子网和联合储能子网间的功率交互,制定功率协调控制策略,提出系统模式及工况切换方法;最后,基于Matlab/Simulink仿真平台搭建了交直流混合微电网仿真模型对所提控制策略进行验证。

量子功率标准综述:原理、现状及展望

随着国际单位制(International System of Units,SI)量子化变革的稳步推进和广域落地实施,以更加准确、稳定的量子计量标准替代实物计量标准,已成为计量学领域的重点攻关任务之一。量子功率标准对电能的精准计量将发挥关键作用,可有力保障电能贸易结算、电碳交易的公平和公正。首先,该文从交流功率标准和直流功率标准两方面,对当前国内外功率标准研究现状进行了综述。对于交流功率标准,分别阐述了工频交流功率标准和宽频交流功率标准的基本架构、测量原理,指出基于热电变换器的交流功率标准可实现工频和宽频(百kHz)交流功率的高准确度溯源,而国内外已有交流量子功率标准的工作频带一般不超过400Hz,需开展宽频交流量子功率标准研究;对于直流功率标准,国内外还处于初步研究阶段,由于当前尚缺乏对直流电压、电流信号的标准化定义,导致应以何种形式的直流功率信号作为标准被测对象尚不明确,无法为构建直流量子功率标准提供方向性指导。随后,该文对比分析了不同的功率标准,给出了对当前构建功率标准所存在问题的思考,并试对交、直流功率标准的未来发展做出展望:随着宽频量子电压标准技术的发展与进步,有望实现宽频量子功率标准;同时,开展宽频、宽量限电压、电流放大器和比例技术的研究,是实现高准确度交、直流量子功率标准的重要前提。