An improved analysis method of constant-current charge/discharge curves and its application to nickel hydroxide electrode

The derivative of charge and discharge curves (d t /d E vs E plot) can be used to describe the charge and discharge process more exactly. The d t /d E ? 獷 plots of nickel hydroxide electrode at different charge/discharge rates and intermittent discharge experiment are discussed. Though the d t /d E ? 獷 plot is affected by many factors, it clearly has intrinsic relation with the nature of active material such as conductivity and thermodynamic potential of active material, which changes with the state of charge. The d t /d E—E plot can also be applied to other electrochemical active materials, especially to those having several phases during charge or discharge.

Characteristics of charge and discharge of PMMA samples due to electron irradiation

In this study, using a comprehensive numerical simulation of charge and discharge processes, we investigate the formation and evolution of negative charge and discharge characteristics of a grounded PMMA film irradiated by a non- focused electron beam. Electron scattering and transport processes in the sample are simulated with the Monte Carlo and the finite-different time-domain （FDTD） methods, respectively. The properties of charge and discharge processes are presented by the evolution of internal currents, charge quantity, surface potential, and discharge time. Internal charge accumulation in the sample may reach saturation by primary electron （PE） irradiation providing the charge duration is enough. Internal free electrons will run off to the ground in the form of leakage current due to charge diffusion and drift during the discharge process after irradiation, while trapped electrons remain. The negative surface potential determined by the charging quantity decreases to its saturation in the charge process, and then increases in the discharge process. A larger thickness of the PMMA film will result in greater charge amount and surface potential in charge saturation and in final discharge state, while the electron mobility of the material has little effects on the final discharge state. Moreover, discharge time is less for smaller thickness or larger electron mobility. The presented results can be helpful for estimating and weakening the charging of insulating samples especially under the intermittent electron beam irradiation in related surface analysis or measurement.

Numerical Simulation of Properties of Charged Particles Initiated by Underwater Pulsed Discharge

Governing conservation equations for energy, momentum, mass and charge were deduced. Based upon these equations and the Saha equation, the particle density, temperature and pressure of the channel initiated by underwater pulsed discharge, are simulated. Influence of temperature and pressure on particles density is also analyzed. Some of the simulation results are in an agreement with experimental results. The results will be helpful in further understanding of the formation mechanism of underwater pulsed discharge plasma.

Simulation of Space Charge Impact on Partial Discharge Inception Voltage in Power Busbars Dedicated to Future Hybrid Aircrafts

Reducing greenhouse gases, saving energy resources and mass optimization require technological changes towards increasingly electric vehicles. At the same time, performance improvement of semiconductor and dielectric materials further promotes electronic components confinement, resulting in a significant increase of embedded power densities. In the particular case of future hybrid propulsion aircrafts, electrical power that intended to supply reactors would be converted through power electronics components mounted on power busbars and insulated by solid dielectrics materials. These dielectrics materials have to respond to various electrical constraints of use (HVDC), in spite of environment change of aircraft parameters such as low pressure, temperature and thermal cycles, humidity... Unfortunately, partial discharges phenomenon is the most problem within electrical insulation system (EIS). Based on a topological model of power busbars designed for power converters dedicated to hybrid aircraft, partial discharge studies were conducted by simulation in various charging conditions of a PTFE insulator. Simulation results, which focus on electric field thresholds criteria of partial discharge inception voltage in air, reveal a net sensitivity of a space charge accumulation and distribution on dielectrics behaviour even for low space charge density, depending on their location in dielectrics. Compared to the behaviour observed with implanted homocharges, when by increasing homocharges density from 0.5 C/m3 to 2 C/m3 we observe a decrease of electric field by 450%, simulation results show a highest risk of partial discharge inception when heterocharges are accumulated inside dielectrics. Their accumulation increases the electric field in triple points beyond electric field thresholds of partial discharge inception in air. The simulated electric field reaching 22 kV/mm with only 2 C/m3 of heterocharges density accumulated in dielectric/busbars interfaces.

Characteristics of Nanosecond Pulsed Discharges in Atmospheric Helium Microplasmas

Microplasmas are very interesting due to their unique properties and achievable regimes maintained at atmospheric pressures. Due to the small scales, numerical modeling could contribute to the understanding of underlying phenomena as it provides access to local parameters--and complements experimental global characteristics. A self-consistent formalism, applied to nanosecond pulsed atmospheric non-equilibrium helium plasmas, reveals that several successive discharges can persist as a result of a combined volume and dielectric surface effects. The valuable insights provided by the spatiotemporal simulation results show the critical importance of coupled gas and plasma dynamics--namely gas heating and electric field reversals.

Influence of shape effect on dynamic surface charge transport mechanism of cellular electret after corona discharge

Surface charge accumulation and transport on cellular polypropylene play an important role in nanogenerators,which could have a potential impact on energy harvesting and wearable devices for zero carbon energy systems and the internet of things.Different shapes have different charge accumulation and decay characteristics of the polymer.Therefore,we studied the influence of the sample’s shape on the surface charge decay by experiment and modeling.The surface potential of square and circular cellular polypropylene was measured by a two-dimensional surface potential measurement system with electrostatic capacitive probe.The experimental result shows that the surface potential distribution of the square sample dissipates non-uniformly from the bell shape to a one-sided collapsed shape,while that of the circular sample dissipates uniformly from the bell shape to the crater-like shape.Moreover,the simulated results of the initial surface potential distributions of the square and circular cellular polypropylene are consistent with the experimental results.The investigation demonstrates that the charge transport process is correlated with the shape of the sample,which provides significant reference for designing electret material used for highly efficient nanogenerators.

Modeling and Simulations in Symmetrical Supercapacitors Using Time Domain Mathematical Expressions

This study presents the deduction of time domain mathematical equations to simulate the curve of the charging process of a symmetrical electrochemical supercapacitor with activated carbon electrodes fed by a source of constant electric potential in time ε and the curve of the discharge process through two fixed resistors. The first resistor RCo is a control that aims to prevent sudden variations in the intensity of the electric current i1(t) present at the terminals of the electrochemical supercapacitor at the beginning of the charging process. The second resistor is the internal resistance RA of the ammeter used in the calculation of the intensity of the electric current i1(t) over time in the charging and discharging processes. The mathematical equations generated were based on a 2R(C + kUC(t)) electrical circuit model and allowed to simulate the effects of the potential-dependent capacitance (kUC(t)) on the charge and discharge curves and hence on the calculated values of the fixed capacitance C, the equivalent series resistance (ESR), the equivalent parallel resistance (EPR) and the electrical potential dependent capacitance index k.

Development of River Rating Curves for Simple to Complex Hydraulic Structure Based on Calibrated HEC-RAS Hydraulic Model, in Kwale, Coastal Kenya

Accurate and reliable river flow information is critical to planning and management for sustainable water resources utilization. Most of engineering activities related to hydrologic designs, flood, drought, reservoirs and their operations are heavily dependent on the river flow information derived from river rating curve. The rating curve for a given river section is normally developed from a set of direct stage-discharge measurements for different periods. This involves considerable labour, risk and resources, and presupposes a complex and extensive measuring survey. Extrapolating the rating curve beyond the measured range, as common in many cases, is fraught with errors and uncertainties, due to the complex hydraulic behaviour of the surface water profile in transition from section, channel, downstream and flood plain controls which are often poorly understood with direct measurements. Hydraulic modeling has recently emerged as one of the more promising methods to efficiently develop accurate rating curves for a river section with simple or complex hydraulic structures and conditions. This paper explores the use of a Hydraulic Engineering Center-River Analysis System (HEC-RAS) model to review and develop river rating curves for three hydrometric stations on two rivers in Kwale, coastal Kenya. The HEC-RAS models were set up based on topographical (cross section and longitudinal) survey data for the reaches and engineering drawings for the hydraulic structures commonly used as section controls for flow measurement. The model was calibrated under unsteady state conditions against measured stage-discharge data which were captured using a Velocity Current Meter (Valeport) and an Acoustic Doppler Current Profiler (ADCP) for both low and high flow. The rating curves were extracted from model results and the uncertainty associated with each rating curve analyzed. The results obtained by the HEC-RAS model were satisfactory and deemed acceptable for predicting discharge across the stage range at each river section.

电容屏破损缺陷局部放电过程规律特征及仿真分析

油纸电容式变压器套管因性能好、成本低而被广泛采用。当电容屏存在边缘破损工艺缺陷时易发生局部放电,进而会改变油纸绝缘性能,缩短套管使用寿命,严重时危及电网设备安全运行。为研究电容屏破损局部放电过程变化规律,明确放电发展阶段,该文搭建了缺陷套管放电实验模型分析局放过程中相位谱图、放电量等参数发展规律,并基于实验规律及流体漂移扩散理论、固体双极电荷传输理论,建立了末屏缺陷针板沿面放电过程仿真模型,结合仿真中电荷形态变化、放电时间及油纸界面电荷密度分布对电容屏破损放电过程进行阶段划分:放电初始阶段,铝箔尖端电荷聚集发生电晕放电;放电发展阶段,尖端处带电粒子在电场作用下向油纸发展,小部分达到油纸界面产生沿面放电;放电破坏阶段,经过长时间沿面放电进入油纸发生预击穿,电场强度更大使带电粒子能量更高,冲击油纸表面造成油纸表面纤维素断裂炭化形成通道。仿真结果与实验结论相对应,证明了仿真的有效性。该文的研究成果进一步阐明了油纸套管电容屏工艺缺陷局部放电的过程及机理。

电动汽车双层优化模型的充放电调度策略

传统的分时电价策略虽然一定程度上可以改善电动汽车无序充电所产生的电网日负荷峰谷差加大、负荷率降低等状况,但易产生新的负荷高峰,并且当前多目标优化等策略削峰填谷效果欠佳或用户参与度不高。针对上述问题,提出一种基于双层优化模型的调度策略以充分考虑电网和用户两侧需求。第1层模型以优化电网日负荷方差最小为目标函数;第2层优化模型建立以车主充电成本最小以及保证用户出行需求的目标函数,然后用改进的粒子群-模拟退火算法对双层优化模型进行循环迭代求解,并将第2层优化后的结果反馈给第1层,以此循环优化,输出最终结果。对比优化前后的负荷曲线,结果表明:与当前优化策略相比,所提出的基于双层优化模型的V2G调度策略能有效降低新的负荷高峰及负荷峰谷差,减少参与V2G的用户成本,实现两侧双赢。

播撒碘化银人工消雹对冰雹云微物理过程和起放电过程影响的数值模拟研究

为了全面了解人工消雹对云中冰相粒子的浓度和时空变化以及冰雹云微物理过程和起放电的影响,本文利用包含了AgI催化方案的三维强风暴动力电耦合数值模式,以AgI播撒量为唯一变化量进行了多组模拟实验。结果表明,催化过后,整体上,-40~0℃范围内的冰晶、雪花和霰粒子数浓度和比含水量增多。播撒AgI使霰的平均尺度减小,向雹的转化比例大为降低,因此冰雹的比含水量和浓度都减小。随着AgI播撒剂量的增加,冰晶、雪花和霰粒子的数浓度和比含量整体变化趋势不变,增大与减小区域相对应,但变化更明显;消雹效果会更好,但降雨量呈先增加后减小。播撒AgI会使冰雹云前期正的非感应起电率区出现时间提前,中心增强,上界高度抬升,后期负的非感应起电率区中心增强。所以,播撒后前期主要使底部次正电荷区增强,后期主要使上方主正电荷区和中部负电荷区增强。随着催化剂量增多,这些变化越明显。播撒AgI对地闪有一定的抑制作用,而使云闪和总闪少量增多,首次放电和云闪的峰值时间提前,放电持续性更强,闪电频发时段的闪电频率略有降低。

基于风冷的锂离子电池充放电设备热特性影响研究

针对锂离子电池充放电设备内电池组温升过高、温度一致性不好的问题,以风冷系统充放电设备为研究对象,基于数值传热学理论,建立热力学计算模型并结合测试验证。通过抽象充放电设备散热特征,提取了两个影响电池组热特性的主要因素。针对不同托盘通风结构及不同风机布局分别设计了研究方案,并分析了不同托盘通风孔、不同托盘环形风口、不同风机位置及不同风机数量对电池组热特性及充放电设备流场的影响。结果表明:充放电设备放电温升测试数据与仿真数据接近,说明热力学模型准确;托盘通风孔对电池组热特性有一定积极影响,但作用有限;托盘环形风口通过提升电池表面湍动能强度,增强电池表面对流换热效果,从而对电池组热特性起关键作用;风机位置正对电池时,电池组具备更好的换热效果;风机数量与电池组热特性呈正相关关系,当风机数量为6时,既能满足电池组热特性,又能提高系统能耗。研究结果可为锂离子电池充放电设备的热特性管理提供一定的指导。

基于COMSOL多物理场的冲击电压下变压器绝缘油中流注放电的仿真研究

随着超高压、特高压设备和输电系统的发展,矿物油以其优异的介电性能、老化稳定性和安全性能被广泛应用于电气设备的绝缘中。模拟了流注放电在油中的传播过程,分析了电场强度和空间电荷变化的结果,研究了不同外加电压和不同针-球间距下变压器放电模型的模拟结果,比较了不同条件下流注放电过程的特点和发展,最后确定了不同因素对流注放电形成和发展的影响。

锂离子动力电池不同调荷方式下放电性能的研究

结合实际项目经验,针对锂离子电池在开发过程中采用Pack环模进行低温放电功率标定后对整车冬季低温放电性能进行验证时两者存在差异的现象,通过采用二阶Thevenin等效电路模型来研究分析电池的充放电机理,并根据电芯的脉冲充放电的实测结果对电池的极化现象进行研究与分析,识别出了不同调荷方式下对放电性能带来的差异。采用控制变量法重新采用不同的调荷方式对Pack环模低温功率标定方法进行调整及验证后,最终Pack环模得到的放电性能结果和整车进行低温放电性能的验证结果一致,从而可为后续Pack环模进行低温放电功率标定试验来模拟整车冬季低温放电性能验证的方法设计及改善整车低温的动力性提供指导,并能一定程度上提前识别整车开发问题及风险,对于缩短电动汽车整车的开发周期具有重要意义。

基于多维高斯模型的单体蓄电池特性离群评估装置研发

在单体电池的生产制造过程中,细微的不一致性(品控问题)及长期充放电运行过程中的复杂因素导致电池组工作时出现单体电池的电压、内阻和SOC不一致,进一步加剧了电池组性能的不均衡。这种不一致性可能引发类似于“木桶效应”的情况,其中劣化最严重的电池单体影响整个电池组的性能,甚至导致电池组报废,缩短了使用寿命。蓄电池在充放电过程中的特性变化包括内阻的变化,因此需要确保每个单体的特性在充放电过程中同步变化,即每个蓄电池单体的充放电特性曲线是重合或接近重合的。尽管核容试验关注整组电池容量和规定放电时长后单体电压是否达标,但缺乏对蓄电池动态特性曲线的充分反映。现存的异常单体一致性测试方法基于硬性标准和大数据,不适用于同组运行电池组的单体异常查找,也存在简便性的不足。

电动汽车采用不同充放电策略的影响评价研究

电动汽车由于其显著的节能减排潜力,已成为未来交通领域的重要转型方向。然而,电动汽车的充放电行为主要由用户决定,每辆车接入电网都会引起随机的电力负荷波动。在我国以燃煤为主要电源结构的情况下,未经调控的随机充电行为将导致交通领域的减排效益转移到发电端,使电动汽车发展的节能减排目标失去实际意义。因此,电动汽车的发展需要重点研究充放电策略。充放电策略有无序充电策略、有序充电策略和V2G策略三种方式。本文总结了电动汽车充放电负荷的影响因素,主要包括电动汽车类型、电池容量、日行驶里程、充电起始时间、充放电功率、电价等,根据统计概率对这些主要影响因素建立了概率统计模型,并使用蒙特卡洛模拟法预测电动汽车负荷,得到不同充放电策略下满足电动汽车电力需求的日负荷曲线。然后,使用重庆市实际数据进行仿真,探究在实际条件下,规模电动汽车用户采用无序充电、有序充电、V2G对电网、环境和用户等各方面的影响,为利益相关者提供决策依据,并根据结论提出科学、合理、有前瞻性的管理建议。

空气中沿面流注放电表面电荷分布特性的仿真研究

绝缘子表面积聚的电荷会畸变电介质表面电场进而引发沿面闪络。为研究空气氛围中绝缘介质表面在沿面流注放电发展过程中动态电荷积聚情况,在自主开发的二维流体沿面放电仿真模型中增加化学反应体系,模拟了正负极性沿面放电在起始及发展过程中流注自身特性以及介质表面电荷分布特性的演化过程。研究发现施加电压为负极性时,介质表面始终累计负电荷,沿面流注头部累积电荷量极高,流注头部后方界面处电场极性反转,正离子向介质表面运动;施加电压为正极性时,沿面流注头部累积正电荷,尾部电子朝介质表面扩散,介质表面总电荷量为负值。

电缆在地球同步轨道空间等离子体环境中表面充放电性能

针对宇航用电缆可靠性评价问题,分析了卫星用电缆在地球同步轨道空间等离子体环境中的表面充放电机理,设计了地面模拟试验,并通过试验对电缆的表面充放电性能进行了研究,之后针对电缆在空间中长时间使用有可能出现破损裂痕的现象,通过试验对比对破损电缆进行了表面充放电性能的研究。研究结果表明:在地球同步轨道空间等离子体带电环境中,电缆表面电位可能达数千伏,并伴随峰-峰值数安的静电放电;破损电缆在破损处会产生放电使放电电流注入电路,可对电缆内部电路连接的其他器件产生影响。

计及动态非均匀热特性的储能软包锂电池充放电热路模型

当前锂离子电池热行为解析模型与仿真模型在储能应用中面临效率或精度挑战。提出一种计及动态非均匀热特性的软包锂电池热分析方法,为储能系统提供电池状态在线评估工具。首先,构建热路模型和解析偏微分方程组,以捕捉充放电过程中电池动态非均匀热特性。其次,建立迭代机制确定求解参数,发展一种兼顾精度和效率的求解算法。将热解析模型和算法应用于商用储能锂电池温度评估。多种充放电工况下的实验结果表明,所提方法具有毫秒级计算成本和小于3%的温度误差,参数标定、迭代机制增强了该方法的工程适用性。该方法对储能电池管理系统展现出良好的应用潜力。

近树木条件下高压架空输电线路电场特性研究

高压架空输电线路邻近树木时存在树木尖端电晕放电烧灼与输电线路闪络的安全隐患,严重时甚至可能造成线路停电。为研究树木附近架空输电线路的电场分布特性,分别采用变步长和有限元网格剖分的方法来配置导线和树木模型中的模拟电荷和匹配点。运用模拟电荷法对线路走廊内存在树木时水平排列的500 kV架空输电线路的电场分布展开计算,结果表明:树木上方的电场强度随着树木数量和种植密度的增加而减小;当树木的位置由中心导线向边相导线偏离时,树冠上方的电场强度先减小后增大,在偏移距离为14 m时达到最大值20.5 kV/m;根据最短路径平均电场强度确定了树木与500 kV导线之间的最小净空距离为1.2 m,为线路走廊植被管理提供了参考依据。