Characteristics of the electromagnetic wave propagation in magnetized plasma sheath and practical method for blackout mitigation

“Magnetic window”is considered as an effective method to solve the communication blackout issue.COMSOL software package based on the finite element method is utilized to simulate the propagation of right-handed circularly polarized wave in the magnetized plasma sheath.We assume a double Gaussian model of electron density and an exponential attenuation model of magnetic field.The propagation characteristics of right-handed circularly polarized wave are analyzed by the observation of the reflected,transmitted and loss coefficient.The numerical results show that the propagation of right-handed circularly polarized wave in the magnetized plasma sheath varies for different incident angles,collision frequencies,non-uniform magnetic fields and non-uniform plasma densities.We notice that reducing the wave frequency can meet the propagation conditions of whistle mode in the weak magnetized plasma sheath.And the transmittance of whistle mode is less affected by the variation of the electron density and the collision frequency.It can be used as a communication window.

Evaluating the reliability of distributed photovoltaic energy system and storage against household blackout

Distributed energy resources have been proven to be an effective and promising solution to enhance power system resilience and improve household-level reliability.In this paper,we propose a method to evaluate the reliability value of a photovoltaic(PV)energy system with a battery storage system(BSS)by considering the probability of grid outages causing household blackouts.Considering this reliability value,which is the economic profit and capital cost of PV+BSS,a simple formula is derived to calculate the optimal planning strategy.This strategy can provide household-level customers with a simple and straightforward expression for invested PV+BSS capacity.Case studies on 600 households located in eight zones of the US for the period of 2006 to 2015 demonstrate that adding the reliability value to economic profit allows households to invest in a larger PV+BSS and avoid loss of load caused by blackouts.Owing to the differences in blackout hours,households from the 8 zones express distinct willingness to install PV+BSS.The greater the probability of blackout,the greater revenue that household can get from the PV+BSS.The simulation example shows that the planning strategy obtained by proposed model has good economy in the actual operation and able to reduce the economic risk of power failure of the household users.This model can provide household with an easy and straightforward investment strategy of PV+BSS capacity.

Mitigation of blackout problem for reentry vehicle in traveling magnetic field with induced current

In this paper, a novel solution mitigating the radio blackout problem is proposed, which improves existing traveling magnetic field(TMF)-based methods. The most significant advance lies in replacing the external injection with self-induced current, which does not require electrodes. The improved analytical model is derived to evaluate the electron density reduction taking into consideration the self-induced current for various TMF velocities. The plasma reduction performance is analyzed for several conditions including the total absence of injected current. The results show that the velocity may be used to trade off the injected current and, when sufficiently large, eliminates the need for an injected current while mitigating radio blackout. The effectiveness of this solution to the blackout problem is demonstrated in commonly used aerospace communication bands. With a field strength of less than 0.15 T, increasing the velocity from40 m s^-1 to 3100 m s^-1 is all that is required to obviate the need for an injected current. Moreover,typical reduction ratios for electronic density tolerance(2, 1.9, 1.75 and 3 times for the L-, S-, Cand X-bands, respectively, at an altitude of 40 km) remain unchanged. Increasing the velocity of the TMF is much easier than injecting current via a metal electrode into a high-temperature flow field. The TMF method appears practical in regard to possible future applications.

HVDC Grid Segmentation Analysis for Blackouts Reduction

Segmentation of large AC systems through DC links introduces a new concept that utilizes the advantages of direct current transmission to improve network reliability and increase power transfer capacity. Technical literature argues that the segmentation of the AC network and the introduction of DC links at these systems connection points bring benefits to system operation, once contingencies generated on one side of the DC connection point would not be reflected on the other side of DC connection, thereby reducing the likelihood of cascading shutdowns and blackouts due to load restraint on transmission lines and transformers. Amidst this scenario, this paper presents a study of the main topics regarding the use of this new network segmentation philosophy, bringing a practical point of view for the use of this concept at the electrical power system planning. The effect of DC segmentation before a contingency that would initiate major outages in an adapted electrical system model IEEE-14 bus is studied and simulations have been performed with test HVAC systems and segmented by HVDC link. The results have been compared, principally in relation to the voltage bus, reactive power generation, system losses and power flow at the lines, and demonstrated that this new concept improved the grid reliability.

基于正交电磁场的等离子体电子密度控制

正交电磁场是一种极具应用前景的降低等离子体电子密度、消除再入通信黑障的控制方法。根据离子质量与动量的守恒原理,建立了正交电磁场控制的物理模型;通过与流体力学方程的比拟,应用隐式格式实现了物理模型的稳定求解。通过数值模拟研究了正交电磁场控制装置中外加电场强度、磁场强度等参数对等离子体电子密度控制效果的影响规律,发现:在电流及磁场作用下,洛伦兹力使得电子发生漂移,导致局部电子密度下降,出现电磁窗口;电压越高、磁场越强,控制效果越好;对于相同磁场,电压较低时,电子密度减小量与电压基本成线性关系,电压超过100 V后,两者关系的非线性逐渐增强。由此,本文制造了电子密度控制原理样机,并在等离子体实验平台中进行了实验,采用发射光谱法和微波干涉法测量诊断了等离子体的电子密度变化情况,在控制区内得到了局部低电子密度区,证实了洛伦兹力作用下等离子体的漂移以及对等离子体电子密度的控制作用。

航天返回舱雷达探测技术研究

雷达在探测航天返回舱黑障区时,因受到等离子体鞘套干扰,长期存在跟踪不稳定甚至丢失等问题。本文从等离子体鞘套与电磁波相互作用机理出发,提出了航天返回舱黑障区电磁特性仿真方法和再入场景回波仿真方法;结合仿真与实测数据研究获取黑障区目标回波特征,提出了基于鞘套快时变特性的目标检测方法;设计了返回舱黑障区认知探测流程,将其应用于多频段雷达装备成功完成了多次返回舱探测任务,保障了黑障区稳定跟踪,基本解决了航天返回舱黑障区雷达探测问题。

考虑次生故障差异化影响下韧性主动提升的输电系统网架重构策略

近年来,我国能源电力加速转型,极端自然灾害频发,国际形势不稳定,使得常规安全风险与非常规安全风险交织,大停电风险有增加的趋势。稳健可靠的网架重构方案对防止恢复中再次发生系统崩溃具有重要意义,针对当前研究中未有效计及恢复中次生故障的不足,该文提出一种考虑次生故障差异化影响下系统韧性主动提升的网架重构策略。首先,讨论在网架重构恢复方案中考虑次生故障影响的必要性;然后,基于分割多目标风险分析方法提出一种系统韧性指标,旨在差异化处理次生故障并突出高风险故障对恢复过程的影响;进一步建立考虑韧性主动提升的网架重构全局优化模型,以增强系统对高风险故障的抵御能力。为提高模型的求解效率,提出一种基于窗口滚动机制的求解策略,可给出兼顾快速性与稳健性的网架重构方案。最后,采用新英格兰10机39节点系统和IEEE 118节点系统验证所提出方法的有效性。

基于KL散度距离处理风电不确定性的负荷恢复分布鲁棒优化

在构建以新能源为主体的新型电力系统的背景下,在恢复控制过程中积极利用新能源并充分应对其对运行安全带来的潜在风险对于减小停电损失具有重要意义。首先,为了表征风电出力的不确定性,采用KL散度(Kullback-Leibler)距离作为筛选极端风电出力场景的控制条件,并据此构建模糊集作为风电出力典型场景。在满足相关运行安全约束的前提下,建立了以最大化加权负荷恢复量为优化目标的分布鲁棒优化模型以制定计及风电的负荷恢复方案。经松弛处理和对偶转换所得到的混合整数二阶锥模型可调用商业求解器求解。以接入规模风电场的IEEE 10机39母线系统为例进行仿真,结果表明:相比于传统的鲁棒优化方法,该方法降低了优化结果的保守性,有助于加快负荷恢复,减小停电损失。

On power system blackout modeling and analysis based on self-organized criticality

This paper makes a comprehensive survey on power system blackout modeling and analysis based on SOC (self-organized criticality). Firstly,a generalized SOC theory from the viewpoint of cybernetics is introduced. Then the evolution model of power system and its relative mathematical description,which serves as a concrete example of the proposed generalized SOC,are given. Secondly,five blackout models capturing various critical properties of power systems in different time-scales are listed. Finally,this paper analyzes SOC in power systems,such as,the revelation of criticalities of proposed models in both micro-scale and macro-scale which can be used to assess the security of power system,and cas-cading failures process.

双极型LCC-HVDC直流系统作为黑启动电源的启动方法及策略

科学合理的黑启动电源及方案是应对电网灾变停电的最有效策略,可加快其系统恢复进程,大幅减少停电损失。双极型换相换流器型高压直流系统(LCC-HVDC)具有调节灵活输电容量大的优势,但其作为黑启动电源存在一定的困难。提出了以双极型LCC-HVDC为黑启动电源的黑启动方法及完整过程,实现向受端无源网络恢复供电,以加速其恢复进程。首先给出了双极型LCC-HVDC作为黑启动电源时所面临的问题及相应的解决策略;进而给出了双极型LCC-HVDC作为黑启动电源恢复向受端无源网络恢复供电的实现过程。该过程包括2个阶段,第1阶段实现双极型LCC-HVDC的仿融冰模式启动;第2阶段为从仿融冰模式过渡到向受端无源网络恢复供电过程。算例证实了该启动方法的有效性和正确性。该方法使双极型LCC-HVDC具备了黑启动能力,并利用直流系统为受端电网的系统恢复过程提供了电压和频率支撑。

Texas Electric Power Crisis of 2021 Warns of a New Blackout Mechanism

The Texas electric power crisis that occurred in February 2021 has drawn great attention internationally due to its severity and for not having been foreseen.In this rapid communication,we classify the 2021 Texas electric power crisis as an energy insufficiency-caused power crisis,which alerts of a new blackout mechanism.Different from capacity insufficiencycaused power crises in the past,the Texas electric power crisis of 2021 directly resulted from the long-duration extreme cold weather as well as fundamentally from the insufficiency of sustainable supply capability of energy.We begin this paper with a brief retrospect of the event and its consequences.Definitions of energy/capacity insufficiency-caused power crises are given,as well as an overview of the supply and demand during the event,based on realistic operation data.Quantitative simulations are then conducted to reveal the underlying reasons for the power crisis and reveal how to better prepare for the future.Finally,several insights and suggestions on handling the new mode of blackout in the future are proposed and discussed.

基于加权潮流熵和耦合支路介数的大停电故障集构建方法研究

随着电网互联程度的加深,电网因连锁故障引发大停电的概率增大,构建连锁故障集是预防大停电的有效措施之一。首先,研究对电网稳定运行影响巨大的故障支路集,定量评估电网运行状态的加权潮流熵计算方法。然后,结合全过程动态仿真软件,提出基于加权潮流熵和耦合支路介数的大停电故障集构建方法。最后,以某地区电网为例验证所提方法的正确性和有效性。该方法既考虑电网结构变化又考虑电网状态变化,能够准确反映电网故障动态过程。

基于巴西“8·15”大停电事故的仿真分析与思考

2023年8月15日,巴西发生大面积停电事故,对经济社会正常运转造成严重影响。事故暴露出巴西电网结构薄弱、电源支撑不足、技术防线不完善、安全管控有短板等问题,为我国电力安全和新型电力系统建设工作带来诸多启示。为模拟巴西大停电发展全过程,文章基于大电网在线安全分析应用平台,调整某地区电网运行方式,削弱网架结构,并使北部新能源大发,设置包含直流闭锁在内的复杂连锁故障,使电网解列为南北两片区,并采取低频减载、失步解列、高频切机等安控措施,使电网恢复安全稳定运行,对日常调控运行工作具有一定指导意义。

The August 14, 2003 blackout andits importance to China

本文作者P .JeffreyPaleimo先生系美国KEMA公司的资深电力专家 ,2 0 0 4年 1月在上海就美加8·14大停电事故及中国电网的安全运行同我国同行进行了交流、探讨。首篇刊出特邀P JeffreyPaleimo就8·14美加大停电原因、涉及的电力体制以及中国和亚洲的电力市场应引以为鉴作了专题论述。结合美国国内的各新闻报道和评论 ,以美加大停电特别工作小组的中期报告作为依据 ,归纳了大停电发生的原因 ,特别指出美国现行电力体制中出现的对长距离输电时的地区由于协调控制薄弱 ,增加了发生大停电的可能性。指出 ,在中国东部地区 ,国民经济每年以 10 %以上的速度发展 ,对电力系统发展具有很高的要求是必然的 ,因而对现有电力系统要不断重新评估分析 ,设计中要考虑隔离点 (breakpoints) ,保证必要时以孤岛模式运行。

基于时变隐马尔科夫模型的连锁故障预测

近几年,电力系统大面积停电事故在国内外多有发生,而这些事故都是由连锁故障所引起。因此,分析其发展机理、预测其发展路径成为相关学者重点关注的问题。针对目前预测方法比较单一、不能全面考虑连锁故障的影响因素等问题,文章提出时变隐马尔科夫预测模型,该模型改进了马尔科夫模型中的状态转移矩阵;充分考虑了支路保护/断路器拒动、误动概率;系统支路硬件故障概率;支路使用年限等方面因素。文中基于系统拓扑结构计算支路间的故障状态转移概率矩阵,对该矩阵进行不同的改进,通过对比不同模型的预测结果,优化改进,得到连锁故障传播路径,最后,用IEEE 36模型验证所提方法的可行性和准确性。

Numerical and experimental studies on the effectiveness of time-varying electromagnetic fields in reducing electron density

When an aircraft or a hypersonic vehicle re-enters the atmosphere,the plasma sheath generated can severely attenuate electromagnetic wave signals,causing the problem of communication blackout.A new method based on time-varying E×B fields is proposed to improve on the existing static E×B fields and mitigate the radio blackout problem.The use of the existing method is limited by the invalid electron density reduction resulting from current density j=0 A m^(-2)in plasma beyond the Debye radius.The most remarkable feature is the introduction of a time-varying electric field to increase the current density in the plasma to overcome the Debye shielding effect on static electric field.Meanwhile,a magnetic field with the same frequency and phase as the electric field is applied to ensure that the electromagnetic force is always acting on the plasma in one direction.In order to investigate the effect of time-varying E×B fields on the plasma electron density distribution,two directions of voltage application are considered in numerical simulation.The simulation results indicate that different voltage application methods generate electromagnetic forces in different directions in the plasma,resulting in repulsion and vortex effects in the plasma.A comparison of the vortex effect and repulsion effect reveals that the vortex effect is better at reducing the electron density.The local plasma electron density can be reduced by more than 80%through the vortex effect,and the dimensions of the area of reduced electron density reach approximately 6 cm×4 cm,meeting the requirements of electromagnetic wave propagation.Besides,the vortex effect of reducing the electron density in RAM-C(radio attenuation measurements for the study of communication blackout)reentry at an altitude of 40 km is analyzed.On the basis of the simulation results,an experiment based on a rectangular-window discharge device is proposed to demonstrate the effectiveness of the vortex effect.Experimental results show that time-varying E×B fields can reduce the electron density in plasma of 3 cm thickness by 80%at B=0.07 T and U_(0)=1000 V.The investigations confirm the effectiveness of the proposed method in terms of reducing the required strength of the magnetic field and overcoming the Debye shielding effect.Additionally,the method is expected to provide a new way to apply a magnetic window in engineering applications.

巴基斯坦“2023.1.23”大停电事故分析及启示

2023年1月23日,巴基斯坦电网发生大停电事故,损失负荷11356MW,持续时间接近22h,引发广泛关注。该文首先介绍巴基斯坦电力系统的电源、电网及负荷概况;然后,梳理此次大停电事故的各阶段发展过程,从网架结构、运行方式、涉网保护、防御措施、事故恢复、重要用户6个方面分析大停电事故的直接和间接原因;最后结合中国电力系统特点及面临的新形势,提出保障大电网安全稳定运行、防止大面积停电的相关措施建议。

基于斯皮尔曼相关系数和系统惯量的中国电网停电事故趋势预测

在能源形势紧张和绿色发展的背景下,全球范围内的新能源发电规模在不断扩大。然而近年来国外发生的几起大规模停电事故说明了新能源的广泛接入给电力系统的安全运行带来了新的挑战。与此同时,中国提出“3060”双碳目标和建设以新能源为主的新型电力系统目标,使得电网中新能源装机发展迅猛,导致电力系统惯量水平下降,电网运行的风险水平进一步提高。为更好地认识电网的停电事故和惯量水平之间的关系,该文分析中国电网年均停电事故损失负荷与系统惯性常数之间的相关性。首先,基于斯皮尔曼相关系数对中国电网年均停电事故损失负荷绝对值和相对值与系统惯性常数进行相关性分析。其次,分析随着时间推移,中国电网年均停电事故损失负荷与系统惯性常数两者相关性的变化情况。然后,在宏观层面,预测中国电网未来年均停电事故损失负荷的发展趋势。