性能优良的电流型控制逆变电源

三态电流滞环控制策略通过引入恒定频率的时钟信号和鉴频鉴相电路,有效地克服了三态离散脉冲调制(Discrete Pulse Modulation,简称DPM)电流滞环控制策略的缺陷。分析研究了三态电流滞环控制逆变器的电路拓扑、三态电流滞环控制策略、稳态原理特性、以及关键电路参数的设计准则。设计并研制成功的1 kVA 190 VDC/115 V400 HzAC逆变器原理样机具有变换效率高,体积重量小,输出频谱特性优,输出波形质量高,静态精度高,动态响应快,负载适应能力强,音频噪音低,成本低等优良的综合性能。     

Estimation of synchronous machine parameters from performance relations

The parameters of synchronous machines are required in system analysis, fault calculations, sizing of cables, circuit breaker selection, power factor correction, and voltage drop calculations. One of the major stumbling blocks is the general lack of design and application data. The design information is generally restricted and not commonly available to all users. Furthermore, the parameters are difficult to obtain through field measurements. In this paper, a mathematical model is presented to estimate the parameters of a synchronous machine from name-plate details. The data used in the estimation include output kVA, voltage, current, speed, rated power factor, field voltage, field current, and short-circuit ratio. The equations are derived from a well-known performance model and solved using a spreadsheet program available on any personal computer. Two case studies are presented in this paper. There is reasonable agreement between the estimated and available parameter values. Finally, the usefulness of this procedure and some of the limitations are outlined.     

船舶轴带无刷双馈电机短路电流分析与保护设计

当船舶轴带无刷双馈电机(BDFG)功率绕组发生三相短路故障时,短路电流会对系统造成较大的危害。因此,有必要设计专门的保护电路保障系统的安全。利用空间旋转坐标系,建立船舶轴带BDFG功率绕组三相短路时的动态方程,并依据磁链守恒定律研究系统短路电流的变化特性。通过分析短路电流的各个分量,提出加入撬棒电阻和直流卸载电路的保护方式来卸载过电流,并进一步研究加入保护电路后的电流变化特性。以1台30 kVA的BDFG为仿真对象,运用MATLAB/Simulink进行模型仿真和理论值计算,验证了保护电路的有效性,对船舶轴带BDFG电气安全设计具有指导意义。     

基于自适应神经元的短路电流参数提取

真空断路器实现选相分闸的关键是快速提取短路电流参数。传统快速傅立叶(FFT)和最小二乘参数估计方法由于响应速度慢、计算量大难以满足选相分闸的实时要求；该文基于自适应神经元，给出了一种真空断路器同步开断短路电流时快速提取短路电流参数，预测电弧熄灭时电流零点的方法。介绍了自适应神经元估计短路电流参数的基本原理，采用正交滤波器消除衰减直流分量和误差自相关估计自适应改变学习步长，加快神经元的学习收敛速度和减少稳态误差。MATLAB仿真验证了所提方法的快速性和有效性。     

测控系统电路板专用智能故障诊断仪

文中介绍一种功能多,故障定位准确,操作方便,价格低廉测控系统电路专用智能故障诊断仪,使用该仪器,可有效地缩短电路故障排除时间,从而提高设备利用率。该仪器的设计思想和结构特点对于其他电路的故障诊断亦有参考价值。     

采用一种新控制方法的并联有源电力滤波器

介绍了10kVA三相四线制并联有源电力滤波(Shunt Active Power Filter,简称SAPF)的研制、系统构成和工作原理,以及采用负载基波电流作为参考电流的新型控制模式.设计了基于DSP和CPLD的控制电路,最后给出了实验结果.实验证明,该系统能有效补偿非线性负载产生的谐波,不仅补偿精度高,而且动态性能优良.     

组合型光伏并网发电系统

采用功率组合技术,通过功率主电路单元并联,运用移相PWM并联组合技术,实现系统结构模块化,可组成大功率光伏并网发电装置,提高系统故障冗余能力,保证系统安全可靠运行。系统采用非线性解耦控制策略及最大功率寻优、空间矢量PWM控制,进行电流跟踪,可调节电网功率因数,且电压适应范围宽。以移相PWM并联组合技术为基础,采用3个单相20kVA的光伏并网发电装置组成60kVA三相光伏并网发电装置,已投入运行。     

经济型三相饱和铁芯故障限流器

故障限流器是限制高压电网短路故障电流的有效措施。由于高压故障限流器存在限流器是单相结构、励磁容量大、损耗高、体积大和成本较高等问题,提出了一种经济型三相饱和铁芯故障限流器结构。该结构采用三相共用铁轭方式,能有效限制电网的各种短路故障电流,具有永磁体涡流损耗小、永磁体可靠性提高、铁芯磁性材料和永磁体用量小等显著优点。首先介绍了经济型三相饱和铁芯故障限流器的工作原理,建立其等效电路和磁路模型。其次采用有限元方法分析了经济型三相饱和铁芯故障限流器各种状态的阻抗特性和磁场分布特性。最后设计并研制出限流器小容量试验模型,开展了试验研究。仿真和试验结果均证明了文中所提出方法和结构的可行性和有效性。     

适用于两电平电压源型换流器的直流故障清除辅助拓扑

两电平电压源型换流器在35kV及以下电压等级输电场合具有较高的成本效率比,因此被广泛应用于风电并网等低压领域。但是,其不具备直流故障清除能力的特点,给电网设备安全造成了较大的影响。基于以上背景,文中提出了适用于两电平电压源型换流器的直流故障清除辅助拓扑。该辅助拓扑使用超导故障电流限制器,大幅降低了故障电流;基于电流谐振的思路,可实现在电流过零时将故障清除。采用该辅助拓扑的直流故障清除方案,相比于采用交流断路器的方案,具有清除时间短、故障电流小的优点;相比于采用直流断路器的方案,具有电压变化率小、成本低的优点。最后,在PSCAD/EMTDC中验证了所提辅助拓扑的正确性与有效性。     

Motor Contribution During Three-Phase Short Circuit Fault

One of the major factors to be considered in selecting the ratings of electrical equipment (circuit breakers, bus bar bracing, etc.) is the level of three-phase short circuit current available at the equipment location in the system. The total three-phase short circuit current at a faulted point includes both the currents from the power source (such as electric utility company or in-plant generators) and contribution from electrical motors in the system. Presently, the calculation of three-phase fault current in a system is based on the method outlined in IEEE Standard 141-1976 in which the calculation of motor contribution within the system is defined. It will be pointed out that during a three-phase fault, only motors directly connected to the faulted bus or downstream buses will contribute fully to the fault. Other induction motors (with transformers connected between the motors and the fault) may or may not contribute current to the fault point. These motors will continue to receive power from the supply and act as motors. Therefore lower fault current values will be the result. This finding will have a significant bearing on borderline equipment selection with consequent savings in equipment cost. The conclusion is drawn that the calculated short circuit current based on IEEE Standard 141-1976, is higher than the actual value. This leads to unnecessarily high fuse and breaker interrupting ratings, bus bracing, etc. Computer studies and an analysis of this phenomenon are presented.     

自动消弧线圈及接地选线一体化装置的低压模拟试验

为检验自动消弧线圈及接地选线一体化装置的测控系统的各项性能指标,在实验室搭建了低压模拟试验电路,其控制系统可以单片机或者PLC两种方式来实现。文中给出了两种控制方式详细的硬件和软件框图。在所搭建的低压模拟试验环境里对测控系统进行的各项功能性试验表明,所研制的低压模拟试验电路可进行电容电流测量试验、单相接地试验、接地选线试验等多项试验,有一定的推广应用价值。     

基于MMC的多端直流电网通用计算方法及拓扑优化研究

针对现有直流电网直流侧短路简化计算方法普遍不适用于对称单极接线系统及短路故障后故障电流急剧上升导致换流站闭锁的问题,提出了适用于对称单、双极接线方式直流电网的通用计算方法和直流电网拓扑优化方法。首先,分析了不同接线方式下的直流电网直流侧单、双极短路故障特性。其次,基于阻抗频率特性提出了适用于不同接线方式直流电网的故障电流计算方法,并得到了评价故障电流水平的简化指标,有效地评估直流电网拓扑变化时的故障电流水平,实现多端系统的拓扑优化,降低单极接地故障电流水平。最后,通过电磁暂态仿真案例验证了所提计算方法和简化指标的准确性和有效性。     

An Iterative and Cost-Based Approach for Optimal SFCL Allocation in Fault Level-Constrained Meshed Networks

Abstract

In this article, an allocation method for superconducting fault current limiter (SFCL) to reduce the exceeded short circuit current within the breaking capacity of the circuit breakers (CBs) is proposed. A cost-based allocation method is advised because of the high cost of SFCL depending on its type. In this article, the multiple parameters such as number, impedance size and type of the SFCLs in meshed networks are determined by defining a cost function for SFCL and using a new hybrid genetic algorithm and sensitivity analysis (HGASA) optimization. The proposed method is based on gradual (step by step) adding the multiple SFCLs in various points of the network during the iterative-based process to optimal SFCL allocation with the least economic costs in fault level-constrained meshed networks. A sensitivity index based on the average decrease of fault current is proposed to reduce the search space and to improve the efficiency of the algorithm. Also, since the different types of SFCLs have different behavior in fault current mitigation, they are analyzed and considered in this article. IEEE 30-bus test system is chosen to evaluate the accuracy and efficiency of the proposed method.     

Multi objective optimal allocation of fault current limiters in power system

Transmission systems, connection of distributed generation to the grid are increased due to increase in power demands. This fact causes the increase in short circuit level of power networks. The occurrence of fault in such networks leads to large short circuit currents throughout the system, which may exceed the rating of existing circuit breakers and can damage system equipment. There are some approaches to reduce this fault current such as power network reinforcement and utilization of fault current limiter (FCLs) in power systems. Power system reinforcement is too difficult if not impractical. Therefore, the utilization of FCLs can provide an effective way to suppress fault currents. The effectiveness of FCL depends on the number of FCLs and their installation location. In this paper, a novel approach is presented to determine the optimal number and location of FCLs to improve the power network reliability and fault current reduction based on different conflicting objective functions. IEEE 39 BUS system and IEEE 57 BUS system are considered to evaluate the effectiveness and feasibility of the proposed method. The objective functions considered for the optimal allocation are reliability of power system, economic impact and short circuit current reduction. Unlike what has been previously done in literature, in this paper Pareto based optimization algorithms, namely non-dominated sorting algorithm, multiobjective particle swarm optimization and multiobjective evolutionary algorithm based on decomposition, are utilized to deal with this problem. The use of these methods made it possible to obtain the Pareto optimal front in which these objective functions are optimized simultaneously.     

计及保护动作与换相失败的逆变侧阀短路故障定位

鉴于现有阀短路故障定位方法依赖桥臂电流信息,而目前工程实际中存在桥臂电流不易获取、定位精度不高的问题,提出了一种无需桥臂电流的逆变侧阀短路故障定位方法。考虑控保系统对不同位置阀短路故障响应特性以及逆变侧阀短路故障引起的换相失败对故障特征的影响,分析了不同时刻发生逆变侧区内4种典型阀短路故障的故障特征。结合逆变侧保护动作情况和系统电气量特征,设计了不同位置阀短路故障识别判据,进而实现逆变侧换流器区不同位置阀短路故障定位。基于RTDS与实际控保系统的数模混合仿真验证了所提故障定位方法的有效性。     

手持式电缆故障测试仪系统实现

针对目前国内生产的电缆故障测试仪存在造价高、携带不便、需要交流供电、安全性差等缺点,研制出一种性能优良、功能相当、价格低廉、适合野外作业的手持式产品.该产品的系统实现基于脉冲反射原理,以TMS320VC5409和CPLD为处理核心,由低压脉冲产生器模块、高速A/D转换器模块、USB控制器等组成.本文详细介绍了该系统的工作原理、硬件与软件实现方案和实验测试分析.该仪器达到了一定的精度,能较好地适用于工程现场的测量应用.     

基于NCAV和电路等效替换的PWM整流器容错控制系统

三相脉冲宽度调制(pulse width modulation,PWM)整流器因其具有可控的功率因数、网侧三相电流趋于正弦、直流侧电压稳定等优点,在电机控制、风力发电并网、柔性直流输电和微电网等领域得到广泛应用。为了提高三相PWM整流器可靠性,文中提出了一种PWM整流器容错控制系统,该系统结合了归一化电流平均值(normalised current average value,NCAV)故障检测法和基于电路等效替换的容错方法。该控制系统在功率开关管单管开路故障情况下能够实现故障检测和诊断,并进行快速的容错控制,从而减少单管开路故障对系统造成的影响,改善故障下三相电流波形,减小输出电压纹波,提升系统的整体性能和可靠性。通过仿真验证了该控制系统的有效性。     

用于不平衡负荷的D-STATCOM数学建模与系统仿真

不平衡负荷无功补偿及分相控制的配电系统用静止同步补偿器(D-STATCOM)动态性能好、谐波含量小、功率密度大,可实现无功功率的实时、就地以及不平衡负荷平衡化补偿。为研究其特性和在系统中的应用,首先定义了二值逻辑开关函数,分别建立D-STATCOM在abc三相坐标系下的微分方程与传递函数动态数学模型;然后根据瞬时无功功率理论建立了不平衡负荷指令电流检测系统与D-STATCOM的直接电流控制方式;最后分别基于数学模型及装置器件模型,应用不平衡负荷指令电流检测方法与直接电流控制建立D-STATCOM双闭环系统,在三相四线制配电系统中对D-STATCOM系统的静态、动态性能进行了仿真分析。仿真结果验证了所建数学模型的正确性以及指令电流检测系统和直接电流控制方式的有效性,表明用于不平衡负荷动态无功补偿的D-STATCOM具有良好的动态性能与静态补偿效果。     

多端口电感耦合型直流限流断路器快速重合闸策略

高压直流（high voltage DC,HVDC）电网是连接可再生能源与交流主网的主要载体,直流故障后的恢复速度对整个交直流电网的稳定性有重要影响。基于多端口电感耦合型高压直流限流断路器,提出一种与直流电网换流器控制策略相配合的快速重合闸策略。介绍了多端口限流断路器的拓扑结构,分析了换流器控制策略对故障隔离后直流电压的影响,并对限流断路器的重合闸时序进行了选择,形成了与风电场等弱交流系统连接的换流器-断路器协调配合重合闸的控制策略及逻辑流程。在4端双极直流电网仿真模型中,验证了所提重合闸策略具有冲击电流较低,故障恢复时间较短的优势。     

具有短路限流功能的统一潮流控制器设计

统一潮流控制器(UPFC)在电力系统发生短路故障时,其串联变换器极有可能因承受系统高电压和大电流的冲击而损毁。针对该问题,提出了一种新型柔性交流输电系统装置——具有短路限流功能的统一潮流控制器(简称限流式UPFC),给出了其主电路拓扑结构、工作原理和控制策略。PSCAD/EMTDC软件的建模和仿真结果表明,在电网正常运行状态下,该装置特性等效为常规UPFC;当电网在装置安装点附近发生短路故障时,装置中的限流器模块能立即自动从零阻抗转变为高阻抗,将系统及流经UPFC的短路电流限制到较低数值,保护了UPFC免受系统高电压和大短路电流的冲击,同时也降低了系统的短路电流水平,增加了系统的可靠性和经济性。