An Online Fault Detection Model and Strategies Based on SVM-Grid in Clouds

Online fault detection is one of the key technologies to improve the performance of cloud systems. The current data of cloud systems is to be monitored, collected and used to reflect their state. Its use can potentially help cloud managers take some timely measures before fault occurrence in clouds. Because of the complex structure and dynamic change characteristics of the clouds, existing fault detection methods suffer from the problems of low efficiency and low accuracy. In order to solve them, this work proposes an online detection model based on asystematic parameter-search method called SVM-Grid, whose construction is based on a support vector machine(SVM). SVM-Grid is used to optimize parameters in SVM. Proper attributes of a cloud system's running data are selected by using Pearson correlation and principal component analysis for the model. Strategies of predicting cloud faults and updating fault sample databases are proposed to optimize the model and improve its performance.In comparison with some representative existing methods, the proposed model can achieve more efficient and accurate fault detection for cloud systems.

Influencing Factors of the Power Fluctuation on the Ultra High Voltage Transmission Line Caused by Faults at the Remote Ends of the Interconnected Grid

After the North China grid and the Central China grid get into connection with the UHVAC demonstration, a new phenomenon is discovered according to some simulations. That is, the faults at the remote end of the UHV interconnected grid will result in significant power fluctuation and voltage drop on the UHV transmission line and even system splitting. But the faults near the UHV line only have marginal effects. Further, the simulation results also indicate that the short-circuit current of the buses near the UHV line is larger than that of the buses far away from the UHV line. This phenomenon is divergent from the traditional view. In this paper, the detail will be introduced, and the factors influencing the system stability after faults are presented and analyzed. The results indicate that transmission power of the UHV line and of the lines between the remote end and the major grid influence the fluctuation on UHV line. The load model and the grid structure of the remote end also have effect on it. Finally, corresponding control scheme is presented to improve the operation conditions of the UHV interconnected grid and ensure its security and stability.

Revised Fault Free Analysis Method for Reliability Evaluation of Smart Grids

Smart grid was proposed as a practical form of future power distribution system. Evaluating the reliability of smart grids was of great importance and significance. A revised fault tree model was proposed to distinguish and separate grid-connected operation mode and islanded operation mode of smart grids,focusing on the perspective of the consumers. A hierarchical Monte Carlo simulation method for reliability evaluation was also proposed based on the proposed fault tree model. A case of reliability evaluation for the future renewable electric energy delivery and management( FREEDM) system was carried out and analyzed. The proposed methods can be applicable to other forms of smart grids.

Fault Identification and Islanding in DC Grid Connected PV System

Nowadays, the DC distribution system has been suggested, as a replacement for the AC power distribution system with electric propulsion. This idea signifies a fresh approach of issuing energy for low-voltage installations. It can be used for any electrical application up to 20 MW and works at a nominal voltage of 1000 V DC. The DC distribution system is just an extension of the multiple DC links that previously available in all propulsion and thruster drives, which typically comprise more than 80% of the electrical power consumption on electric propulsion vessels. A fault detection and islanding scheme for DC grid connected PV system is presented in this paper. Unlike traditional ac distribution systems, protection has been challenging for dc systems. The goals of this paper are to classify and detect the fault in the PV system as well as DC grid and to isolate the faulted section so that the system keeps operating without disabling the entire system. The results show the measured values of power at PV panel and DC grid side under different fault condition, which indicates the type of fault that occurs in the system.

Review of Fault Types, Impacts, and Management Solutions in Smart Grid Systems

Fault management study in smart grid systems (SGSs) is important to ensure the stability of the system. Also, it is important to know the major types of power failures for the effective operation of the SGS. This paper reviews diverse types of faults that might appear in the SGS and gives a survey about the impact of renewable energy resources (RERs) on the behavior of the system. Moreover, this paper offers different fault detection and localization techniques that can be used for SGSs. Furthermore, a potential fault management case study is proposed in this paper. The SGS model in this paper is investigated using both of the Matlab/Simulink and the Real Time Digital Simulation (RTDS) to compute the fault management study. Simulation results show the fast response to a power failure in the system which improves the stability of the SGS.

基于s-grid的断层一体化建模方法

根据断层两盘的空间位置关系和s-grid相邻网格间的关系,提出一种网格与断层的拟合方法("构造断层面法"),依据各地层的关系将断层划分成不同高程平面的结构体,通过将断层破碎带作为网格拟合对象的一部分,最终达到一体化建立断层的效果,并给予了破碎带可被编辑的地质属性。该拟合方法可在工程中提升建模精度,防止锯齿状边界的出现,使得三维模拟情况更加贴近实际情况。同时,断层破碎带亦可根据工程需求进行属性传递,保证了断层两盘的属性连通性。

基于波形特征提取和FA-Grid SVM的MVB故障诊断

列车通信网络的故障诊断一直是列车健康管理的难点,文章针对列车MVB(多功能车辆总线)网络,提出了一种基于波形特征提取和联合萤火虫网格寻优支持向量机(FA-Grid Support Vector Machines, FA-Grid SVM)相结合的故障诊断方法。通过提取MVB总线物理波形的时域特征,作为支持向量机的样本,构建MVB故障数据集;基于SVM较优参数点基本集中于同一区域这一现象,提出FA-Grid两步寻优的参数优化模型。试验结果表明,与传统网格寻优和遗传算法(GA)相比,提出的FA-Grid寻优模型时间复杂度低,分类效率高,能够准确地对MVB故障进行诊断。

Model for Anticipating Failures by Omission in Calculation Grids

Computer grids are infrastructures in which heterogeneous and distributed resources offer very high computing or storage performance. If they offer extreme computing performance, they are also subject to the appearance of many failures related to this type of architecture. While performing tasks, if the response time of a node in the system incomprehensibly exceeds the requirements of the specifications, the node experiences an omission failure. The task running in the failed node will be unavailable until the node resumes normal activity. Waiting not being a possible solution, many fault tolerance methods have been proposed. Despite this large number of fault tolerance methods on offer, computer grids are still prone to many failures by omission. In this work, a numerical study of the failures by omission which occur in the calculation grids during the execution of the tasks was carried out and a model allowing anticipating its failures was proposed with the formalism PDEVS (Parallel Discret EVent system Specification).

Fault Ride-Through(FRT)Behavior in VSC-HVDC as Key Enabler of Transmission Systems Using SCADA Viewer Software

The world’s energy consumption and power generation demand will continue to rise.Furthermore,the bulk of the energy resources needed to satisfy the rising demand is far from the load centers.The aforementioned requires long-distance transmission systems and one way to accomplish this is to use high voltage direct current(HVDC)transmission systems.The main technical issues for HVDC transmission systems are loss of synchronism,variation of quadrature currents,amplitude,the inability of station 1(rectifier),and station 2(inverter)to either inject,or absorb active,or reactive power in the network in any circumstances(before a fault occurs,during having a fault in network and after a fault cleared),and the variations of power transfer capabilities.Additionally,faults impact power quality such as voltage dips and power line outage time.This paper presents a method of overcoming the aforementioned technical issues using voltage-source converter(VSC)based HVDC transmission systems with SCADA VIEWER software and dynamic grid simulator.The benefits include having a higher capacity transmission system and proposed best method for control of active and reactive power transfer capabilities.Simulation results obtained using MATLAB validated the experimental results from SCADA Viewer software.The results indicate that the station’s rectifier or inverter can either inject or absorb either active power or reactive power in any circumstance.Also,the reverse power flow under different modes of operation can ride through faults.At a 100.0%power transfer rate,the rectifier injected 775.0 W into the network.At a 0.0%power transfer rate,the rectifier injected 164.0 W into the network.At a-100.0%rated power,the rectifier injected 1264.0 W into the network and direction was also changed.

Comparison the Performances of Three Earthing Systems for Micro-Grid Protection during the Grid Connected Mode

This paper presents, tests and compares three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types during the connected mode. The main contribution of this work is including the models of all the micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included in the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the connecting mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current protection relays. With using TN system, Touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited value if current limiter is included with the transformer of the main grid which connects MG. For the two others earthing systems (TT and IT), fault current is small and nearly equal to the over load current which make over current protection relay can not differentiate between fault current and overload current. All models of micro sources, earthing systems, inverters, main grid and control schemes are built using Matlab?/Simulink? environment.

Simulation the Wind Grid Code Requirements for Wind Farms Connection in Kosovo Transmission Grid

This paper presents aspects of study and simulation approach for planned wind power projects in Kosovo Power System in relation with Grid Code requirements. All generators, connected to the Kosovo Transmission System are required to comply with the Grid Code. The Grid Code was originally developed with conventional synchronous generators. Since Wind Turbine Generators don’t have the same characteristics as synchronous generators, it was considered appropriate to develop a new set of Grid Code provisions specifically for Wind Farm Power Stations in relation with specific characteristic of Kosovo Power System. With high excepted penetration of wind power, a simultaneous loss of Wind Farms generation will put in the risk the security and reliability of Power System. Therefore, the main requirements for Wind farm power stations concern the fault ride through capability, frequency operation range, and reactive power capability of wind turbines. In the case of grid faults wind turbines have to supply a definite reactive power depending on the instantaneous voltage level of connection point and they must return quickly to normal operation.

Malicious Node Detection Using Confidence Level Evaluation in a Grid-Based Wireless Sensor Network

In this paper, we present a malicious node detection scheme using confidence-level evaluation in a grid-based wireless sensor network. The sensor field is divided into square grids, where sensor nodes in each grid form a cluster with a cluster head. Each cluster head maintains the confidence levels of its member nodes based on their readings and reflects them in decision-making. Two thresholds are used to distinguish between false alarms due to malicious nodes and events. In addition, the center of an event region is estimated, if necessary, to enhance the event and malicious node detection accuracy. Experimental results show that the scheme can achieve high malicious node detection accuracy without sacrificing normal sensor nodes.

基于广域信息分析的智能配电网故障自愈技术研究

针对传统电网接地故障检测和自愈方法存在识别速度慢且精确度较低的问题,文中结合信号广域信息提出了一种配电网故障自愈方法。该方法构建了单相接地故障模型,并将零序电流作为分析的对象。将零序电流信号分解为时域、频域以及小波域分量来作为广域特征向量,并采用随机森林算法对其权重进行分类,利用LightGBM算法对分类后的广域特征向量加以训练,进而得到故障预测结果。在仿真测试中,所提算法能够抵抗过渡电阻与初始相位角变化对预测结果的影响,且其故障分析准确率的平均值为98.9%,在对比算法中为最优,表明该算法可为配电网故障自愈提供有效的技术支撑。

Design and Testing of Three Earthing Systems for Micro-Grid Protection during the Islanding Mode

This paper presents and tests three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types when the MG transferred to the islanding mode. The main contribution of this work is including the models of all micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included with the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the islanding mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current pro-tection relays. With using TN earthing system, touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited values during islanding mode. For the two others earthing systems (TT and IT), fault currents are small and nearly equal to the over load currents which make over current protection relay can not differentiate between fault currents and overload currents. All models of micro sources, earthing systems, inverters and control schemes are built using Matlab?/Simulink? environment.

不对称短路故障下永磁直驱风电机组并网控制策略研究

电网侧发生不对称故障时,永磁直驱风电机组并网电流会发生三相不平衡的问题。针对这一问题,提出一种基于自适应陷波器的网侧换流器控制策略。该控制策略基于解决机组并网电流二倍频分量的思想,在电网侧发生不对称短路故障时,将进入逆变器的dq坐标系下的二倍频电压分量去除,从而使得网侧换流器输出的电流达到三相平衡。本文首先分析了电网侧发生不对称短路故障后永磁直驱风力发电机组的动态响应;然后建立了机侧和网侧换流器的模型,并分别采用了双闭环矢量控制技术和基于自适应陷波器的控制策略;最后进行仿真分析,验证了改进后的控制策略相较于传统控制策略,有效解决了不对称短路故障下并网电流三相不平衡问题。

虚拟同步机电流受限暂态电压支撑机理与改进故障穿越控制研究

针对虚拟同步机在电网低、过电压故障下所面临的无功电压支撑不足、特性差等问题,建立考虑电流限幅特性的虚拟同步机等效电路模型,并基于拓扑同伦原理,给出不同无功电压控制在等效电路相量图上的几何表征方法。利用该方法,揭示几种常见无功电压控制下的虚拟同步机电流受限暂态电压支撑机理,并由此提出一种改进的故障穿越控制策略,有效改善电网低电压、过电压故障下的暂态电压控制能力和支撑特性,进而缓解故障期间的暂态功角稳定问题。基于PSCAD/EMTDC仿真对所提机理和故障穿越控制方法进行详细验证,最后,在3机9节点系统中对其在近、远区电网故障下的支撑特性进行仿真验证。

Effect of Distribution Generators on Stability in a Limited Bus Power Grid System

It has been recognized recently that when injecting renewable energy source power to a load bus which connected to a distributed feeder in a power grid system, a stability problem occurs particularly when having high fault duties that exceeding the circuit breaker ratings at some substations. In this paper an analysis of power flow, short circuit, stability and protection is given in detail to an example of limited 7-bus power grid system. Comparison is illustrated between power grid with and without distributed generators regarding bus voltages, fault currents, critical power angles, selected current transformers and over current relay settings in each bus.

基于混合型MMC的柔性直流电网故障电流阻断控制策略

柔性直流电网是实现大规模可再生能源发电汇集、输送和并网的有效手段。针对基于混合型MMC的直流故障电流阻断方案会引起功率传输中断的问题,本文提出了一种混合型MMC负压控制与超高速机械开关协调配合的故障电流阻断方法,该方法能够快速阻断故障电流并维持非故障线路的功率传输。通过分析故障电流组成及关键影响因素,确定了换流站的控制目标,基于全桥子模块的电压调节自由度,提出了利用混合型MMC输出负压主动吸收故障电流的控制策略,并设计了其与超高速机械开关的协调配合方案,实现故障的可靠隔离。最后,基于RTLAB实时数字仿真平台搭建了四端柔性直流电网仿真模型,仿真结果表明,本文提出的方法可快速阻断直流故障电流,缩短直流电网功率恢复时间,提高系统安全稳定性。

含跟网和构网型新能源发电单元的混联电力系统暂态同步稳定分析

在新能源发电单元与同步发电机共同接入的混联电力系统中,不同同步方式新能源间,新能源与同步发电机间耦合复杂,深刻影响系统的暂态同步稳定性。为揭示电网对称短路故障下不同发电单元间的动态耦合机理及其对系统暂态同步稳定性的作用机制,该文首先建立故障条件下混联系统的暂态稳定分析数学模型。随后,利用空间矢量图示法与相平面法分析跟网型新能源发电单元注入电流、锁相环参数以及构网型新能源发电单元有功控制环参数等因素对混联系统内各发电单元暂态同步稳定性的影响规律,并据此给出系统控制器参数的设计原则。最后,通过不同工况下的仿真验证理论分析的正确性。