Recovery of coupled networks after cascading failures

With society＇s increasing dependence on critical infrastructure such as power grids and communications systems, the robustness of these systems has attracted significant attention.Failure of some nodes can trigger a cascading failure, which completely fragments the network, necessitating recovery efforts to improve robustness of complex systems. Inspired by real-world scenarios, this paper proposes repair models after two kinds of network failures, namely complete and incomplete collapse. In both models, three kinds of repair strategies are possible, including random selection（RS）, node selection based on single network node degree（SD）, and node selection based on double network node degree（DD）. We find that the node correlation in each of the two coupled networks affects repair efficiency. Numerical simulation and analysis results suggest that the repair node ratio and repair strategies may have a significant impact on the economics of the repair process. The results of this study thus provide insight into ways to improve the robustness of coupled networks after cascading failures.

Modeling cascading failures and mitigation strategies in PMU based cyber-physical power systems

This paper presents a model of cascading failures in cyber-physical power systems(CPPSs) based on an improved percolation theory, and then proposes failure mitigation strategies. In this model, the dynamic development of cascading failures is divided into several iteration stages. The power flow in the power grid, along with the data transmission and delay in the cyber layer, is considered in the improved percolation theory. The interaction mechanism between two layers is interpreted as the observability and controllability analysis and data update analysis influencing the node state transformation and security command execution. The resilience indices of the failures reflect the influence of cascading failures on both topological integrity and operational state. The efficacy of the proposed mitigation strategies is validated, including strategies to convert some cyber layer nodes into autonomous nodes and embed unified power flow controller(UPFC) into the physical layer. The results obtained from simulations of cascading failures in a CPPS with increasing initial failure sizes are compared for various scenarios.Dynamic cascading failures can be separated into rapid and slow processes. The interdependencies and gap between the observable and controllable parts of the physical layer with the actual physical network are two fundamental reasons for first-order transition failures. Due to the complexity of the coupled topological and operational relations between the two layers, mitigation strategies should be simultaneously applied in both layers.

Cascading failure analysis of power flow on wind power based on complex network theory

Cascading failure is a potential threat in power systems with the scale development of wind power,especially for the large-scale grid-connected and long distance transmission wind power base in China.This introduces a complex network theory(CNT)for cascading failure analysis considering wind farm integration.A cascading failure power flow analysis model for complex power networks is established with improved network topology principles and methods.The network load and boundary conditions are determined to reflect the operational states of power systems.Three typical network evaluation indicators are used to evaluate the topology characteristics of power network before and after malfunction including connectivity level,global effective performance and percentage of load loss(PLL).The impacts of node removal,grid current tolerance capability,wind power instantaneous penetrations,and wind farm coupling points on the power grid are analyzed based on the IEEE 30 bus system.Through the simulation analysis,the occurrence mechanism and main influence factors of cascading failure are determined.Finally,corresponding defense strategies are proposed to reduce the hazards of cascading failure in power systems.

An enhanced cascading failure model integrating data mining technique

An enhanced cascading failure model integrating data mining technique is proposed in this paper.In order to better simulate the process of cascading failure propagation and further analyze the relationship between failure chains,in view of a basic framework of cascading failure described in this paper,some significant improvements in emerging prevention and control measures,the subsequent failure search strategy as well as the statistical analysis for the failure chains are made elaborately.Especially,a sequential pattern mining model is employed to find out the association pertinent to the obtained failure chains.In addition,a cluster analysis model is applied to evaluate the relationship between the intermediate data and the consequence of obtained failure chain,which can provide the prediction in potential propagation path of cascading failure to reduce the risk of catastrophic events.Finally,the case studies are conducted on the IEEE 10-machine-39-bus test system as benchmark to demonstrate the validity and effectiveness of the proposed enhanced cascading failure model.Some preliminary concluding remarks and comments are drawn.

Linking strategies to optimize the robustness of multimodal transport network

In view of the problem that the multimodal transport network is vulnerable to attack and faces the risk of cascading failure,three low polarization linking strategies considering the characteristics of the multimodal transport network are proposed to optimize network robustness.They are the low polarization linking strategy based on the degree of nodes(D_LPLS),low polarization linking strategy based on the betweenness of nodes(B_LPLS),and low polarization linking strategy based on the closeness of nodes(C_LPLS).The multimodal transport network in the Sichuan-Tibet region is analyzed,and the optimization effects of these three strategies are compared with the random linking strategy under random attacks and intentional attacks.The results show that C_LPLS can effectively optimize the robustness of the network.Under random attacks,the advantages of C_LPLS are obvious when the ratio of increased links is less than 15%,but it has fewer advantages compared with B_LPLS when the ratio of increased links is 15%to 30%.Under intentional attacks,as the ratio of increased links goes up,the advantages of C_LPLS become more obvious.Therefore,the increase of links by C_LPLS is conducive to the risk control of the network,which can provide theoretical support for the optimization of future multimodal transport network structures.

基于故障安全域的混合级联直流输电系统后续换相失败抑制策略

混合级联直流输电系统兼顾了电网换相换流器(LCC)和模块化多电平换流器(MMC)的优势,具有良好的工程应用前景,但系统逆变侧LCC与MMC间复杂的交直流耦合特性增加了后续换相失败的抑制难度。为此,该文提出了一种应对混合级联系统后续换相失败的协调控制策略。首先,分析了控制器交互期间电气量波动和LCC无功需求对系统恢复产生的不利影响,并在考虑控制器作用和MMC动态无功支撑的基础上建立了多电气量耦合作用下的故障安全域;其次,通过对混合级联系统和基于电网换相换流器的高压直流输电故障安全域对比分析,提出了一种基于MMC和低压限流环节(VDCOL)的协调控制策略,以实现系统后续换相失败抑制和功率快速平稳恢复相协调;最后,基于PSCAD/EMTDC分别在不同严重程度交流故障、不同短路比和不同故障持续时间下进行仿真对比分析,验证了所提协调控制策略的有效性。

复杂网络中的级联失效研究进展

随着网络科学的发展和复杂系统理论的兴起,学者们开始对复杂网络的结构和动力学特性展开深入研究。在复杂网络动力学特征中,级联失效作为复杂网络动力学特征中重要的研究领域之一,描述了一个系统或过程中的一个故障或错误导致其他相关组件或环节的连锁反应性故障。学者们针对复杂网络中的级联失效提出了多种级联失效模型和恢复策略。本文对级联失效的发生机理进行了分析,总结了国内外针对复杂网络中级联失效的研究成果,并概括了应对级联失效的恢复策略,同时指出了现有研究存在的问题与不足之处,为未来的研究提供了一定的思路。

空中航路网络级联失效缓解方法研究

航路级联失效对空中航路网络的承载能力、运输安全及运行效率具有严重负面影响,可能造成巨大的经济损失并引发一系列社会问题。构建了空中航路级联失效传播网络结构,根据航段流量与容量的时变关系定义航段状态,在此基础上,提出了基于辐射距离的流量分配方法,研究不同分配方法下的网络结构、空域容量、交通需求和运行效率等网络性能指标,以确定航路网络级联失效的最佳缓解方法。以华东空管局所辖区域的部分空域为例,对所提方法进行了验证,结果表明,所提基于辐射距离的度分配法和剩余容量分配法相较于传统度分配法和剩余容量分配法,对网络正常航段数量、可用容量比率、交通需求比率和网络效率产生的影响更小,可以有效缓解级联失效对华东地区航路网络的影响。

情报分析中的认知偏见可控性问题:路径、局限及未来方向

[研究目的]厘清认知偏见的内涵、生发机理以及认知偏见在情报分析中的影响,深入剖析认知偏见可控性问题的研究内涵,反思有关认知偏见可控性问题研究的基本思路和存在的局限性,以进一步探究未来的研究方向。[研究方法]通过对认知偏见问题可控性相关研究的梳理,分别从理论内涵、方法策略、研究视角等角度阐明研究的特点、局限性和未来研究方向。[研究结论]研究认知偏见的可控性需要从三个方面着手。一是应该摆脱非理性桎梏,辩证看待认知偏见,侧重优化认知偏见控制策略;二是需要克服主流认知强迫策略的局限性,强化实现认知塑造的偏见控制核心目的;三是要以基于偏见机理的理论研究视角为核心,拓展实证驱动和数据驱动等研究视角,实现对情报分析中认知偏见的综合性研究。

加权电网级联失效的动力学行为

根据实际IEEE118节点系统建立了加权电网的物理模型,考虑网络的电气特征,提出了基于负载容量模式下的级联失效动力学模型,同时理论推导容忍参数和系统调整系数之间的关系,并借助数值仿真验证了理论结果,进而研究了不同攻击方式对电网动力学弹性的影响.研究结果表明,不同攻击策略下加权电网的容量参数取值相差较大.

基于空间距离改进的航线网络级联失效模型

为准确分析航线网络在多种干扰事件影响下的级联失效过程,首先,对以往研究的节点过载、节点状态识别和节点负载-容量关系三个部分进行整合,引入容量参数α、β和过载系数γ,建立一个综合性的航线网络级联失效模型;在此基础上,考虑实际空间距离因素,对传统的全局负载重分配策略进行改进,提出以丧失运输功能的机场为圆心、实际k倍平均航线里程为半径的圆形负载重分配策略。然后,以国内航线网络为例,开展随机、蓄意两种攻击策略下的仿真。结果表明:基于空间距离的负载重分配策略更具有普适性,即传统全局负载重分配策略仅是其中一个特例;同时,航线网络级联失效结果与负载分配半径密切相关,确定合理的负载分配半径,对缓解航线网络级联失效影响有重要意义。

边耦合相依网络动态修复策略研究

为应对边耦合相依网络中因少部分的连边失效引起的网络大面积的结构性破坏甚至崩溃,本文提出了一种基于共同边界连边的边耦合相依网络级联失效修复模型。将修复过程与网络级联失效过程动态结合,同时根据边耦合网络的特征提出了复合冗余度择优修复策略和一种改进的复合冗余度择优修复策略。分别在随机故障和蓄意攻击情况下对ER-ER(Erdős-Rényi随机网络)、SF-SF(scale-free无标度网络)边耦合相依网络进行仿真,与随机修复策略及介数择优修复策略对比,寻找最优修复策略。研究发现在不同结构的边耦合相依网络中的最优修复策略,随着网络连边初始存留比例及故障类型的不同而发生改变,并且能够在更大的连边初始攻击比例下修复网络至初始状态的修复策略,其所需要的迭代步数并不一定最少。

混合级联UHVDC系统换相失败抑制分析

换相失败是基于电网换相换流器的特高压直流输电系统中最常见的故障类型之一。近年来新投运的混合级联特高压直流输电系统的逆变侧仍包含电网换相换流器,因此换相失败无法避免。首先,在分析电网换相换流器触发调节过程的基础上,明确了换相失败控制的投入时刻是影响换相失败抑制效果的关键因素;进一步地,结合白鹤滩—江苏混合级联特高压直流输电受端的结构特点和接入交流系统方式,分析了混合级联拓扑下的换相失败抑制新思路;最后,提出可充分利用逆变侧电压观测点增加、模块化多电平变换器所连接母线的电压响应更为灵敏的特点,来加快换相失败控制的投入速度,提升系统的换相失败抑制性能。基于PSCAD/EMTDC仿真平台验证了该分析的正确性。

级联失效指挥控制网络抗毁性研究

针对现有的级联失效分析对指挥控制网络的作用和机理研究较少,导致抗毁性评估指标难以量化的问题,从复杂网络的角度出发,运用NK复杂网络理论,引入容量-负载模型,建立指挥控制网络级联失效模型,并通过演化仿真的方法定量分析网络参数和修复策略对指挥控制网络抗毁性的影响。实验结果表明,该模型能较好地刻画指挥控制网络级联失效过程,并挖掘指挥控制网络级联失效内在机理,可为指挥控制网络抗毁性分析与优化提供支撑。

电网连锁故障演化机理与博弈预防

连锁反应故障是导致大停电的重要原因。回顾了2003年以来世界范围内3次较为严重的连锁故障造成的大停电事故,通过对连锁故障发展过程的总结,得出了连锁反应故障的演化规律与一般特征。在此基础上,对连锁反应故障的机理进行了分析。文中将博弈思想应用于连锁故障的预防,将电网出现的扰动作为对弈中的进攻方,系统被动的调整作为被动的防御,提出连锁故障的对弈防御策略,一旦电网发生扰动则系统做相应调整,类似于对弈过程二人的交替走步。机理分析表明,这种调整削弱了元件间的关联作用,将系统运行点向远离临界状态的方向移动,因此可有效预防连锁故障。

现代电力系统连锁性大停电事故机理研究综述

对现代电力系统连锁性大停电事故的机理进行了阐述。根据不同的建模出发点将连锁大停电的研究分成2大类:一类是基于潮流计算和稳定分析的研究,主要介绍了基于复杂系统理论的建模分析和模式搜索策略;另一类是基于电网拓扑的研究,主要论述了关于小世界网络模型和无标度网络模型的研究。最后探讨了一些可能的进行电力系统连锁故障研究所需要解决的关键技术问题。

相依网络在不同攻击策略下的鲁棒性

相依网络的鲁棒性是网络科学研究的重点问题之一,目前很多重要的工作都致力于这一问题的研究.基于此,系统研究了相依网络在几种蓄意攻击策略下的级联失效过程,发现了同时考虑两个网络中相依节点度的特性比考虑单侧网络节点度的特性的攻击策略更有效.研究成果不但有助于理解相依网络级联失效的过程,而且为找到相依网络的弱点并进行有效的保护和攻击提供了有益的提示.

无尺度网络中降低相继故障规模的策略研究

在复杂网络的相继故障过程中,主要影响因素包括:网络结构、节点负载量、节点容量、负载重分策略等。针对这些因素,建立了一个无尺度网络的相继故障模型。模型采用的基于节点剩余容量的负载重分策略能较充分地利用网络资源。仿真结果表明,与基于节点度的负载重分策略相比,基于节点剩余容量的负载重分策略能降低网络相继故障的规模约10%;研究还发现只提高网络中"关键"节点的容量也能有效降低相继故障的规模。当无尺度网络具有社团结构时,相继故障的规模要减小约30%。这些结论对降低网络相继故障规模、网络结构的设计及以后的研究具有重要意义。

长江上游梯级电站开发区泥石流的治理工程效果评估与减灾策略——以金沙江白鹤滩水电站为例

[目的]评估灾害性泥石流严重的长江上游梯级电站开发区泥石流灾害治理工程效果,为长江上游同类水电站的泥石流防灾减灾与治理效果评估研究提供思路。[方法]选择金沙江白鹤滩水电站施工区的矮子沟和大寨沟泥石流治理工程为案例,通过2013—2015年连续3a的现场跟踪调查分析,结合模型计算对矮子沟和大寨沟泥石流峰值流量过程进行计算,分别评估2014和2015年矮子沟、大寨沟泥石流治理工程效果,并进行泥石流危险性评价。[结果]基于长江上游梯级电站开发区泥石流灾害特点,提出了长江上游梯级电站开发区泥石流治理工程效果评估模式,并提出了基于风险控制的水电工程泥石流"以排为主,适当拦挡"治理模式与减灾策略。[结论]矮子沟、大寨沟现有的泥石流防治措施在满库的状态下能够满足500年一遇泥石流过流的要求,泥石流危险性小。

加权无标度网络抵制级联失效的鲁棒性研究

针对复杂网络遭遇攻击和随机失效而引发的级联失效问题,提出一种基于介数的节点加权策略,用于探讨加权无标度网络抵制级联失效的鲁棒性。通过数值模拟和理论分析发现,基于介数的策略具有与基于度的策略几乎相同的最优权重参数。在最优权重参数下,基于介数的策略使得网络更具鲁棒性,能显著降低级联失效发生的可能性和发生情况下的级联规模。