基于中间件技术的电网在线监测数据集成系统设计

目前,部分继电保护装置采用电抗变换器以及低通滤波回路。分析了电抗变换器以及低通滤波回路的组成、数学模型以及对高次谐波的影响。得出电抗变换器显著放大了高次谐波,通过MATLAB仿真以及保护装置的实际波形,证明了电抗变换器对高次谐波的放大作用,并对以后的保护装置的开发提出了建议。     

特高压直流输电系统馈入的城市电网谐波渗透特性分析

针对城市电网直流输电落点谐波从高电压等级向低电压等级渗透过程中出现的高次谐波放大现象,基于网络固有结构理论,提出一种城市电网谐波放大分析方法。注意到电缆对谐波跨电压等级渗透的影响,在谐波国标框架下按等效注入谐波电流大小评价其影响,提出等效注入感容耦合度评估其影响机理,并建立电缆分布参数模型,对其系统等值阻抗感容临界条件进行分析。利用多直流落点局部城市电网对所提方法进行分析验证,并与现场测量数据对比,结果表明所提方法能有效判别谐波敏感回路,以及分析电缆对谐波渗透的影响机理。     

一起500kV线路远跳保护误动作分析

针对一起500 kV线路远跳保护误动跳闸事故,分析了三相组式变压器励磁回路,确定了当保护装置内部电压变换器一次侧中性线开路时,因一次绕组励磁电流中的三次谐波分量无法在3个磁路相互独立的绕组中构成通路,从而使一次绕组励磁电流中不含三次谐波分量,导致激磁电势畸变,在二次绕组中产生含有较高三次谐波的尖顶波,造成远跳保护装置感受的电压升高而误动.通过试验仿真验证,并提出了预防措施.     

基于LCL型感应电能双向传输系统的数学模型分析

传统感应电能双向传输系统大多采用单相全桥变换器拓扑,由于功率器件开关频率较高,导致系统存在高次谐波和EMI干扰。基于全桥变换器LCL型感应电能双向传输系统建立各电气量的数学模型,尤其对电气量各次谐波下的解析表达式进行了详细的物理等效和数学推导,并对基频和谐波下的传输功率加以讨论,最后通过Matlab/Simulink仿真和样机实验验证了数学模型的正确性。     

晶闸管调速装置功率因数改善和谐波抑制

一、晶闸管调速装置的功率因数和高次谐波 以电力半导体电路为基础的调速装置,不可避免地会产生功率因数低和各种高次谐波的问题。功率因数低就需要无功补偿。高次谐波影响电网所供电能波形质量。根据我国《电力系统谐波管理暂行规定》,用户注入电网的谐波电流允许值如表一所示。 可控变流装置的功率因素为     

直流电力机车主电路阻容吸收回路电阻过热烧损故障的原因分析及解决措施

分析了直流电力机车主电路阻容吸收回路电阻过热烧损的原因,通过对阻容电路及电阻元件散热条件的改进,改善了高次谐波对直流电力机车的干扰,有效解决了电阻元件的烧损问题.     

非线性负载对光伏电站运行效率和可靠性的影响分析

从用电负载方面对目前太阳能光伏电站普遍存在的问题进行分析,着重指出了非线性负载所产生的电流畸变、高次谐波和高频干扰是对供电系统造成危害的主要因素.文章从负载和供电2个方面提出了改善措施:第一,使用高功率因数、低畸变的高性能电子节能灯具;第二,在逆变器中采用谐波抑制电路和有源功率因数校正电路对高次谐波加以处理,在供电设备端主动对流人的高次谐波和畸变电流加以处理,使负载功率因数提高到0.9以上.     

基于n阶LMS自适应滤波的改进型谐波检测方法

通过分析多种谐波检测方法,提出一种FBD法和ip-iq法相结合的谐波电流检测方法 ,并对低通滤波环节进行改进。首先设计了一种在三相四线制系统中计算相对简单的谐波电流检测方法,在降低算法复杂性的同时保障了灵活性;其次使用添加了闭环回路的n阶LMS自适应滤波算法模块替代低通滤波器模块,能把测得的基波电流反馈到输入电流中,增强了滤波环节的跟踪速度和动态特性;最后通过仿真验证了改进的谐波电流检测方法的优越性和精确性。结果表明,该方法具有较高的应用价值。     

日本的高次谐波问题及对策

随着电力用半导体应用设备的增加,高次谐波的产生和故障成了日本电网的问题.所谓高次谐波是50HZ、60HZ工频繁数倍频率(100、150、200HZ等)的电压或电流.最近,从产业到家庭广泛采用了可控硅和晶体管等电力用半导体应用设备.如:整流器、变换器、循环换流器、交流电力调整器等.因为这些设备通过工频电源正弦波对可控硅.晶体管输入和截出,配合连接物向负荷供直流或可变频的电压或电流.系统的负荷电流只在可控硅导电期间流过形成畸变波形.这种电流除基波外含有多阶高次揩波.图1为其概要,由于高次谐波电压下降影响,电源电压也畸变.     

浅谈高次谐波对电容组的危害

介绍高次谐波在电力系统中对电力电容器的危害以及抑制高次谐波的措施和方法。     

直驱型风力发电变流器低压穿越控制策略研究

研究了直驱型风力发电变流器系统低压穿越控制策略。首先提出了一种对三相电量进行快速准确的正负序分离软件锁相环。在此基础上,为消除直流电压的二次谐波,采用正、负序双电流内环控制不对称运行控制策略。正负序分离软件锁相环采用了正负序级联延时信号消除法,能够实现对三相电压电流基波正负序分量在同步旋转坐标下的快速提取,并且通过选择不同的参数,可以滤除任何次数谐波的干扰。该方法无需采用滤波器,从而同时具备了稳态精确性和动态快速性。现场实验结果表明,该软件锁相环为三相并网型风力发电变流器在电网发生跌落及谐波畸变时提供了良好运行控制提供保障,正负序双电流内环不对称运行的控制策略保证了在电网电压不对称跌落时的正负序分离控制,消除了直流电压的二次谐波。     

基于调制分量卡尔曼滤波的短时扰动检测

提出了一种基于调制分量的低阶卡尔曼滤波模型．实时检测电能质量短时扰动。该方法将三相电压信号的αβ变换结果分解为基波信号和调制信号．提取调制信号的两个特征分量作为新的状态变量,避免了单独设置各次谐波为状态变量,降低模型阶次并提高暂态响应速度。根据暂态时滤波误差发生突变的特征,提出误差比阈值法判断暂态过程的起止时间。通过自适应修正系统噪声方差阵Q．降低模型误差并有效抑制滤波发散现象。Matlab仿真结果表明所提方法比普通卡尔曼滤波和低通滤波器具有更高的稳态精度和更快的暂态响应速度。     

基于电子式电流互感器的差动保护研究

针对区外故障切除后造成差动保护误动很大程度由电流互感器(TA)饱和所致,分析了变压器和发电机差动保护误动的主要原因,提出了一种基于电子式电流互感器(ETA)的差动保护,信号传感器采用不饱和的空心线圈,前段采用悬浮式电源供电,以光纤作为信号传输媒介,保护原理采用成熟可靠的二段式折线比率保护加谐波闭锁.试验结果表明,该方法可防止TA饱和导致的误动,可大幅提高差动保护可靠性.     

Harmonic Mitigation in AC–DC Converters for Vector Controlled Induction Motor Drives

This paper deals with autotransformer-based multipulse ac--dc converters with reduced magnetics feeding vector controlled induction motor drives for improving the power quality at the point of common coupling. The proposed 12-pulse ac--dc converter-based harmonic mitigator consists of an autotransformer alongwith a passive shunt filter tuned for 11th harmonic frequency. This results in the elimination of 5th, 7th, and 11th harmonic currents. Similarly, the proposed 18-pulse ac--dc converter-based harmonic mitigator eliminates the 5th, 7th, 11th, 13th, and 17th harmonic currents, thereby improving the power quality at ac mains. The experimentation is carried out on the developed prototype of autotransformers-based ac--dc converters. Different power quality indexes of the proposed 12-pulse and 18-pulse ac--dc converters are obtained from simulation and verified from experimental results.     

车用催化转化器流场的数值模拟

本文用当量连续法建立了蜂窝载体的流体力学模型 ,并用CFD软件对整个催化器的流场进行了稳态流动数值模拟。模拟结果显示 :气流在圆锥管壁面附近出现了分离并产生较强的扰动 ,造成气流局部压力损失和载体前气流速度分布不均匀 ;此外 ,扩张角越大 ,催化器流速分布不均匀性和压力损失越大 ,但当扩张角增大到一定程度后 ,扩张角对流速分布和压力损失的影响变小。     

Voltage dip generator for testing wind turbines connected to electrical networks

This paper describes a new voltage dip generator that allows the shape of the time profile of the voltage generated to be configured. The use of this device as a tool to test the fault ride-through capability of wind turbines connected to the electricity grid can provide some remarkable benefits: First, this system offers the possibility of adapting the main features of the time–voltage profile generated (dip depth, dip duration, the ramp slope during the recovery process after clearing fault, etc.) to the specific requirements set forth by the grid operation codes, in accordance with different network electrical systems standards. Second, another remarkable ability of this system is to provide sinusoidal voltage and current wave forms during the overall testing process without the presence of harmonic components. This is made possible by the absence of electronic converters. Finally, the paper includes results and a discussion on the experimental data obtained with the use of a reduced size laboratory prototype that was constructed to validate the operating features of this new device.     

Z-Source-Inverter-Based Flexible Distributed Generation System Solution for Grid Power Quality Improvement

Distributed generation (DG) systems are usually connected to the grid using power electronic converters. Power delivered from such DG sources depends on factors like energy availability and load demand. The converters used in power conversion do not operate with their full capacity all the time. The unused or remaining capacity of the converters could be used to provide some ancillary functions like harmonic and unbalance mitigation of the power distribution system. As some of these DG sources have wide operating ranges, they need special power converters for grid interfacing. Being a single-stage buck–boost inverter, recently proposed Z-source inverter (ZSI) is a good candidate for future DG systems. This paper presents a controller design for a ZSI-based DG system to improve power quality of distribution systems. The proposed control method is tested with simulation results obtained using Matlab/Simulink/PLECS and subsequently it is experimentally validated using a laboratory prototype.      

无源滤波装置智能调谐和谐波过流保护

提出了利用智能调谐技术和谐波过流保护技术弥补无源滤波器工作中存在的过程保护功能缺陷,结合案例分析,阐述了智能调谐方案的控制策略、谐波过流保护配置等问题。     

Pulse multiplication in AC-DC converters for harmonic mitigation in vector-controlled induction motor drives

In this paper, an autotransformer with reduced kilovoltampere rating for 24-pulse ac-dc converter fed vector controlled induction motor drives (VCIMDs) is presented for harmonic current reduction. The 24-pulse operation is achieved using dc ripple reinjection technique in 12-pulse ac-dc converters. The proposed novel harmonic mitigator is found capable of suppressing up to 21st harmonic in the supply current. The procedure for the design of autotransformer for proposed ac-dc converter is presented to show the flexibility in the design for making it a cost-effective replacement suitable for retrofit applications, where presently a 6-pulse diode bridge rectifier is used. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. A set of power quality indices on input ac mains and on dc bus for a VCIMD fed from other 24-pulse ac-dc converters are also given to compare their performance. The laboratory prototypes of proposed autotransformers based 12-pulse and 24-pulse ac-dc converters are developed and test results are presented to validate the developed design procedure and the simulation models of these ac-dc converters under varying loads.