基于T-G保护系统的抗病毒网络安全分析模型

攻击者采用病毒、利用脆弱性等方式进行网络攻击,实质是其攻击权限不断扩大,进而导致系统状态变化的过程,针对这一特性,本文对原有的T--G模型和dejure重写规则进行了扩充,增加了攻击图中节点之间权限、连接关系、节点属性的描述和脆弱性重写规则,形成了DTGSA模型;通过对真实的漏洞进行建模和实验,证明此模型对攻击特征有很好的描述能力,能帮助网络管理员预测可能的攻击,进而采取相应的安全措施。     

基于攻击模式的反向搜索攻击图生成算法

在使用攻击图方法分析网络中脆弱性之间关系时,网络规模一直是制约攻击图生成算法效率的根本因素.本文提出了一个基于攻击模式的高效攻击图反向生成算法.首先,对已有网络模型做出改进,提出了新型的基于网络中关键属性的模型,该模型使用子网掩码压缩网络连接关系,达到缩小网络规模的目的.其次,使用网络模型中的关键属性对脆弱性进行描述,...     

基于贪心策略的多目标攻击图生成方法

为解决网络脆弱性分析中攻击图生成方法存在的状态组合爆炸问题,使生成的攻击图能用于网络中多个目标主机的脆弱性分析,本文提出了一种基于贪心策略的多目标攻击图生成方法。该方法引入节点关联关系,采用贪心策略精简漏洞集,从所有攻击路径中选取使攻击者以最大概率获取网络节点权限的攻击路径,生成由这些攻击路径所构成的攻击图。算法分析和实验结果表明,该方法的时间和空间复杂度都是网络节点数和节点关联关系数的多项式级别,较好地解决了状态组合爆炸的问题,生成的攻击图覆盖了攻击可达的所有节点,能够用于网络中多个目标主机的脆弱性分析。     

两种网络环境中权限提升攻击分析与对比

为了分析分离映射网络对权限提升攻击的缓解作用,提出了一种基于损失期望的攻击图建模评估方法.首先根据网络状态和脆弱性信息确定属性节点和原子攻击节点,生成攻击图,然后根据攻击者选取的攻击序列计算其对目标网络造成损失的期望值.基于该方法对两种网络环境中权限提升攻击情况进行了建模分析对比,结果表明分离映射网络对权限提升攻击起到了良好的缓解作用,较传统网络具有明显的安全优势.     

基于信任关系的脆弱性扫描系统的设计与实现

从分析黑客攻击过程着手,设计了一个权限状态转换模型,采用基于目标权限的搜索树描述了信任关系导致的脆弱性.在此模型基础上,设计并实现了一个基于信任关系的脆弱性扫描系统.该系统具有分布式结构,结合主机扫描与网络扫描技术.测试结果表明,系统能够检测到主机间信任关系导致的脆弱性路径,为网络的整体安全评估提供了依据.     

基于智能化状态转移以及权限改进的攻击图构建方法

针对当前攻击图在大范围网络应用中具有时间复杂度以及图形化描述不准确等缺陷,提出了一种基于智能化状态转移以及权限改进的攻击图构建方法:采用智能化状态转移途径构建攻击模型,依据该模型规划相应的攻击图,并在攻击图生成中引入了权限改进体制,该方法以主机间的连接分析为依据,根据网络攻击状态图中不同主机的原始权限,获取攻击权限的改进路径,能够针对网络变换情况调整主机的权限,进而确保相应网络的安全性,针对大规模复杂化网络攻击问题构建有效的攻击图,以确保整体网络的安全性和高效性.通过最终的仿真实验可得,该方法构建网络攻击图的时间较短,具备较低的时间复杂度和较高的扩展性,是一种高效的攻击图构建方法.     

基于累积效应的网络脆弱性扩散分析方法

网络脆弱性评估是一种主动防范技术,意在攻击发生之前对安全态势进行分析进而制定防御措施,但传统的定量分析模型不能对实体间动态交互关系有很好的展现,而且大都不能得出风险扩散的全局化结果。将脆弱性扩散过程类比于社会网络中影响力传播过程,提出了基于累积效应的网络脆弱性扩散分析方法,定义的脆弱性扩散分析模型给出了细粒度级的主体关系结构,利用攻击效果累积特性提出的分析算法可以更准确地刻画脆弱性扩散规则,保证更好的影响范围。最后对该模型和算法进行了实例验证,在模型描述简洁性、分析结果准确性、安全建议合理性等方面的横向比较分析,验证了模型在评估结果直观性和制定成本最小安全措施等方面的优势。     

基于脆弱性关联模型的网络威胁分析

为了解决网络脆弱性建模存在的问题以及威胁评估方法中的不足,结合面向对象技术提出了基于扩展时间Petri网的脆弱性关联模型,通过定义攻击复杂度和危害度因素以及各评估指标的量化方法,给出了脆弱性关联模型的生成算法。结合网络威胁度的计算公式,运用改进的Dijkstra算法给出了无目标导向的网络威胁量化分析方法。该模型能够有效缩减状态空间的规模,适合对复杂网络攻击建模。实验证明了脆弱性关联模型的正确性及其优越的描述性能,基于该模型的威胁分析方法也更为合理、有效。     

复杂攻击网络的概率可控性

计算机网络是当前规模最大,应用最广泛的复杂网络之一,如何提升网络安全评价的精准性,并推动其在大规模网络下的实用性是当前的研究热点。详细总结了攻击模型和脆弱性风险评估等方面的研究现状和进展,针对目前攻击图模型描述的粗粒度和局限性问题,细化攻击图节点至部件级,以有向加权图的直观形式刻画攻击步骤中部件之间的交互过程;同时通过严密的理论推演,得出了复杂攻击网络完全概率可控或者部分概率可控的准则条件,并论证了概率可控性与传统结构可控性的关系;分析结果及实例验证表明,若网络中存在着有效防御的节点,复杂网络仍可在遭受攻击破坏的情形下提供正常的服务功能,同时给出了防御节点选择及控制网络的具体方法。     

基于BNAG模型的脆弱性评估算法

为准确评估计算机网络的脆弱性,结合贝叶斯网络与攻击图提出一种新的评估算法。构建攻击图模型RSAG,在消除攻击图中环路的基础上,将模型转换成贝叶斯网络攻击图模型BNAG,引入节点攻击难度和节点状态变迁度量指标计算节点可达概率。实例分析结果表明,该算法对网络脆弱性的评估结果真实有效,能够体现每个节点被攻击的差异性,并且对于混合结构攻击图的计算量较少,可准确凸显混乱关系下漏洞的危害程度。     

基于多输入信息融合模型的暂态稳定分类

应用一种信息融合模型对电力系统暂态稳定进行分类评估。当电力系统发生故障时,采用该方法可以综合来自电网和发电机的多个信息源对电力系统的暂态稳定进行判别。利用D-S证据理论实现决策级融合,从而提高电力系统暂态稳定评估的可靠性。10机39节点系统被用来进行仿真研究,结果表明,提出的模型比原有的模型更有效。     

A novel recursive approach for real-time transient stability assessment based on corrected kinetic energy

Real-time assessment of transient stability is one of the main issues of power system operators in online applications. This paper proposes a novel recursive approach based on corrected kinetic energy which has the capability of real-time assessment and real time computation of transient stability margin in the power system. This approach considers all details of power system by using network preserving model to simulate transient stability. This paper uses a hybrid method based on the new concept of equal area criterion to estimate initial value of critical point of the system and corrected Kinetic Energy Function to estimate high precision value of the critical point. Also, this paper proposes a recursive method which uses large change sensitively (LCS) analysis to correct initial condition point of the system when the topology of system is changed by a disturbance. In order to validate the proposed method, comprehensive case studies have been conducted on IEEE39-bus test system. Comprehensiveness in considering the details, simplicity in implementation and low computational cost are the outstanding features of the proposed approach. Also, simulation results approve that the proposed approach can be used in real-time application without loss of any detail in the transient stability assessment.     

基于Transformer的多任务暂态稳定评估

电力系统中的暂态功角稳定和暂态电压稳定对于系统安全运行至关重要,而可再生能源接入比例不断提高和核心设备的电力电子化使得传统的暂态稳定评估方法难以适用。因此,本文提出一种基于Transformer的多任务暂态稳定评估模型。该模型利用Transformer的自注意力机制打破传统循环神经网络的串行计算结构,并行计算暂态过程中各个时间点间的相互关系,快速高效的提取时序特征,并且采用门控多任务学习方法同时评估暂态电压和暂态功角稳定问题,提升模型计算精度和计算效率。本文在IEEE10机39节点系统以及含新能源系统中进行仿真和测试验证了本文提出方法的有效性。     

A Nonlinear Coordinated Approach to Enhance the Transient Stability of Wind Energy-Based Power Systems

This paper proposes a novel framework that enables the simultaneous coordination of the controllers of doubly fed induction generators (DFIGs) and synchronous generators (SGs). The proposed coordination approach is based on the zero dynamics method aims at enhancing the transient stability of multi-machine power systems under a wide range of operating conditions. The proposed approach was implemented to the IEEE 39-bus power systems. Transient stability margin measured in terms of critical clearing time along with eigenvalue analysis and time domain simulations were considered in the performance assessment. The obtained results were also compared to those achieved using a conventional power system stabilizer/power oscillation (PSS/POD) technique and the interconnection and damping assignment passivity-based controller (IDA-PBC). The performance analysis confirmed the ability of the proposed approach to enhance damping and improve system’s transient stability margin under a wide range of operating conditions.      

Deriving a transient stability index by neural networks for power-system security assessment

This paper proposes an approach for establishing a transient stability classifier and derives a continuous transient stability index, using a three-layer feed-forward artificial neural network (ANN), for on-line security assessment in large power systems. With the derived stability index, a novel classification scheme creating an ‘indeterminate’ class, is introduced to minimize misclassifications and to improve the reliability of the classification results. Several post-fault abstract attributes about the system generators’ acceleration rates and kinetic energies provide the basis for the stability classification. In order to derive the transient stability index, a semi-supervised backpropagation (BP) learning algorithm, making use of a specially defined error function, is developed. The proposed approach can not only distinguish whether a power system is stable or unstable, on the basis of the specific post-fault attributes, but can also provide a relative stability quantifier. Furthermore, as the number of the selected abstract attributes is independent of the system size, the methodology of the proposed approach can realistically be applied to large power systems. The 10-unit 39-bus New England power system is employed to demonstrate the proposed approach. The numerical results show that the ANN-based classifier can assess the transient stability reasonably well.     

Transient stability of the power system with the effect of the automatic voltage regulator

In this note, the transient stability of the single-machine system with the effect of the automatic voltage regulator is studied, using the direct method of Lyapunov. A new Lyapunov function for stability study of the power system is constructed by the Lagrange-Charpit method. The Lyapunov function is then used to estimate the critical reclosing times for power-system transient stability. The critical reclosing times given by the proposed Lyapunov function are compared to those obtained by numerical integration.     

An improved Backstepping technique using sliding mode control for transient stability enhancement and voltage regulation of SMIB power system

The problem of transient stability and voltage regulation for a single machine infinite bus (SMIB) system is addressed in this paper. An improved Backstepping design method for transient stability enhancement and voltage regulation of power systems is discussed beginning with the classical Backstepping to designing the nonlinear excitation control of synchronous generator. Then a more refined version of this technique will be suggested incorporating the sliding mode control to enhance voltage regulation and transient stability. The proposed method is based on a standard third-order model of a synchronous generator connected to the grid (SMIB system). It is basically implemented on the excitation side of the synchronous generator and compared to the classical Backstepping controller as well as the conventional controllers which are the automatic voltage regulator and the power system stabiliser. Simulation results prove the effectiveness of the proposed method which ameliorates to a great extent the transient stability compared to the other methods.     

时间序列分析在电力系统暂态稳定预测中的应用

提出利用时间离列分析快速预测多机电力系统暂态稳定性的方法。该方法采用ＡＲ时间序列模型，预测故障后发电机转子角的变化趋势，并根据所构造的转子预测模型多项式是否存在极值作为暂稳的识别判据。仿真结果表明，本文法在不同条件下预测结果都是准确有效的。     

大规模风力发电系统暂态分析与综合评估

随着风电等新能源的大规模接入,电力系统的暂态安全稳定问题日益凸显。使用不同的模型和研究方法分析双馈机对电网稳定的影响会得出不同的结论,因此研究暂态稳定需要结合实际电网进行。首先对风电系统的暂态稳定机理进行分析,然后运用一种新型综合评估法对哈密电网十四个主要风电场并网母线的暂态稳定性进行了评估找出系统电压薄弱点。最后通过仿真,分析了不同风电渗透率、不同故障位置及不同故障类型下其对电网的影响。仿真结果表明,所提出的综合评估法具有计算量小、综合性强等优势;大规模风电机组接入对系统暂态稳定的影响具有双重性。     

Multimachine power systems: Stability, decomposition, and aggregation

A new approach is proposed for transient stability analysis of interconnected power systems, which is based upon the concept of vector Lyapunov functions and the decomposition-aggregation method. The approach results in an exact procedure for computation of stability region estimates which are expressed explicitly in terms of system parameters. More refined models of the subsystems can be readily accommodated by the new approach. In particular, the transfer conductances are included in the present study, a feature which is almost exclusively missing in transient stability analysis of multimachine systems by Lyapunov's method.