逆变器并联运行的环流反馈控制

逆变器并联运行时由于各模块输出电压的频率、相位等参数不一致,会在模块间产生环流。先分析了逆变器并联运行时环流产生的原理。然后对加入和未加入环流反馈控制的并联逆变器系统结构做出比较,结果表明加入环流反馈控制后,其输出电压不变,环流大大减少,两台逆变器的输出电流趋于一致。最后用Matlab软件对此并联系统进行了仿真研究,验证了控制方式的可行性。     

横联差动及和相电流保护装置无法正常投入原因分析

通过实例计算证明并不是所有并列运行的双回线路都适于装设横联差动及和相电流延时速断保护装置;结合现场实际分析横联差动及和相电流延时速断保护装置在重负荷长线路双回线应用时无法正常投入原因。     

多变流器并联系统零序环流控制方法分析

新能源技术的发展要求电力电子设备不断提高功率,促使了电力电子设备并联系统的产生。文中通过分析多个变流器并联系统的平均值模型,对多变流器并联系统的零序电流产生的原因进行了简单的分析,给出了两种可行的零序环流抑制方法。为了进一步分析两种方法的效果,文中建立了SIMULINK仿真模型。仿真结果表明,PI控制和无差拍控制均可对零序环流有较好的抑制作用。但是PI控制的抑制效果更加稳定,更加适合实际应用。     

变压器差动保护用电流互感器饱和的原因分析及解决办法

针对沙角A电厂脱硫变压器差动保护用电流互感器在较小的一次电流下发生饱和的现象,从电流波形、互感器的稳态饱和特性、暂态饱和特性等方面进行了分析计算,并根据分析结果,提出了解决办法,取得了预期效果。     

LCL滤波的风力发电网侧变流器不同控制结构下的性能研究

风力发电系统中LCL滤波器的电网侧电流反馈和变流器侧电流反馈都可用作电流闭环控制,但不同的电流反馈控制结构会对变流器产生不同的影响.分别在理想电网无阻尼电阻、非理想电网无阻尼电阻和理想电网有阻尼电阻3种情况下对风力发电网侧变流器进行了分析.建立了电网电压定向的同步旋转dq坐标系下的风力发电网侧变流器数学控制模型,其中PI控制器被用于补偿被控电流的误差.根据推导出的不同电流控制结构下的闭环传递函数,对其进行了根轨迹分析.通过分析及仿真发现变流器侧电流反馈控制结构相对于电网侧电流反馈控制结构控制算法较复杂,但是系统稳定性好,电网电流的谐波畸变率较低,而电网侧电流反馈控制结构尽管抗电网扰动性较强,但调节器参数受到很大限制,系统动态响应速度较慢,稳态精度较低.     

Measurement of leak current generation distribution in PEFC and its application to load fluctuation testing under low humidification

A study was performed to establish a method for measuring the position and amount of leak current increase during operation of a fuel cell. This measurement method was applied to load fluctuation testing at low humidification and the increase in the leak current was observed in the downstream zone of the cell. The tested cell was disassembled and cross sections were observed under the SEM. The SEM images revealed the formation of a Pt band near the cathode catalyst in the downstream zone of the cell. This may be the cause of the degradation of the membrane at the downstream. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(1): 1–9, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21038     

Inverter for interchangeable use as current source inverter and voltage source inverter for interconnecting to grid

We propose a novel inverter that can be operated either as a current source inverter (CSI) or as a voltage source inverter (VSI) by changing only the control signals. It is proper to use it for interconnecting systems with renewable energy, such as photovoltaic cells or wind generation systems, to a grid. This inverter is usually operated as a CSI connected to the grid. Even if the energy source has a lower voltage than the grid, energy can be supplied to the grid through the proposed inverter. The power factor can be brie?y maintained close to unity. When power supply from the grid is interrupted, the proposed circuit should be operated as a VSI in the stand‐alone operation mode. In this way, the circuit can maintain a constant output voltage to the loads. In this paper, the proposed circuit con?guration and the control schemes for both the CSI and the VSI are described. The circuit characteristics for both are also discussed experimentally. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 45–53, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22349     

电网故障下双馈风电机组暂态电流评估及分析

为了便于分析并网双馈风力发电机组低电压穿越(LVRT)运行的承受能力,有必要对电网故障下双馈风电机组的暂态电流进行评估.本文利用双馈发电机定、转子磁链的暂态变化机理,推导并提出了双馈风电机组在机端短路故障和电网电压不同跌落程度时的定、转子暂态电流评估的解析表达式,并通过考虑风力机传动链柔性的机组暂态仿真结果验证了推导表达式的正确性.在此基础上,应用推导的表达式对双馈风电机组在不同初始输出有功功率、无功功率以及电网电压不同跌落程度时的定、转子暂态电流最大值进行了计算,并得到了不同运行工况对机组暂态性能的影响规律.     

Studies of characteristics and design of superconducting fault current limiter with adjustable trigger current level in current limiting operation

Superconducting fault current limiters (SCFCLs) are expected to improve not only reliability but also stability of power systems. To introduce an SCFCL in a power system, various specifications such as trigger current level, impedance in current limiting operation, recovery time, and so on are necessary. Fault analyses point out that accuracy of the trigger current level is necessary. Therefore, an SCFCL of a transformer type with adjustable trigger current level was proposed and manufactured. Using the trial SCFCL, adjustability of the trigger current level was confirmed. It is found that the SCFCL has good limiting and recovery characteristics. In this paper, characteristics of the SCFCL are considered from a design point of view. Most of the specifications necessary for design depend on the characteristics in current limiting operation. Therefore, the characteristics of the SCFCL in current limiting operation are discussed. It is shown that this kind of SCFCL has good property for easy design, and its design principle is summarized. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 30–38, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10054     

超高压长线电容电流对差动保护的影响及补偿对策仿真分析

采用ATP软件建立了超高压长线模型 ,分析了超高压长线各种故障情况下 ,分布电容对分相电流差动的影响 ,并对比了采用电容电流补偿和不采用电容电流补偿的相量差动与故障分量差动原理的动作情况。仿真结果表明 ,分相电流差动在原理上完全适用于超高压长输电线路的保护 ,在各种运行工况下 ,采用电容电流补偿可以有效提高差动保护的可靠性和灵敏度 ,在同一工况下 ,故障分量差动比相量差动有更好的选择性     

Control of sub‐harmonic oscillation in peak current mode buck converter with dynamic resonant perturbation

In this paper, a dynamic resonant perturbation (DRP) method is proposed to control sub‐harmonic oscillation in a peak current mode controlled buck converter. Different from the traditional non‐feedback resonant parametric perturbation method, the proposed DRP method extracts an approximate sinusoidal control signal from the output voltage. The self‐stabilizing condition for the designed control signal is presented, and its analog circuit implementation is given as well. Furthermore, the system stability boundary is obtained by investigating the system eigenvalues, and the control parameter is effectively determined. The presented simulation and experiment results show that the proposed DRP method eliminates sub‐harmonic oscillation without sacrificing the peak value of the inductor current and features with a self‐stabilizing characteristic for external condition changes. Copyright © 2014 John Wiley & Sons, Ltd.     

新技术手段在变压器差动保护励磁涌流识别中应用研究的现状

励磁涌流的鉴别一直是变压器保护中一个关键问题。在介绍各种新技术手段的原理基础上,着重分析了各种技术目前在变压器励磁涌流识别方面应用的研究及其特点、性能和存在的问题,并指出了这些新技术在今后变压器保护应用中可能的发展方向。     

接地网电流分布的测量与分析

由于在实际接地网中测量接地网电流是不可能的，因此，提出了一种实验室接地模拟的方法来分析实际接地网的电流分布，即在实验水池中，用电量隔离传感器测量接地网的电流分布，测出不同接地网——单根垂直接地体、十字形接地网、水平接地网、复合接地网的电流分布，所得的实验结果为研究接地网中的电位分布及接地网的设计提供较准确的科学数据。     

可调阻抗无互联线并联逆变器的控制方法

传统的无互联线并联逆变器PQ下垂法是由同步电机并网理论推导而来的,它具有稳态均流精度低和动态响应差等缺点.分析了逆变器并联系统的有功功率和无功功率的环流模型,并且基于传统的PQ下垂法,增加了具有阻抗调节功能的两个控制环节,提高了系统的动态和静态环流抑制能力,并且降低了系统对线阻抗等参数不平衡的敏感程度.仿真和实验结果均验证了该方案的良好性能.     

变频器对风电系统轴电压和轴电流的影响

在现代风力发电系统作中,由于大量采用了高频电力电子器件,给整个系统带来了轴电流问题,严重影响着系统的安全运行和发电机轴承等机械部件寿命。精确分析发电机内部电容参数对准确预测轴电压和轴电流的重要作用。首先分析了风力发电系统的共模电路,通过研究风力发电机内部结构,确定了电机耦合电容的解析计算公式,同时提出了有限元计算方法。等效分析轴承运行过程中轴承等效电容模型,进而确定了风力发电机系统轴电流形成机理和影响因素。     

An analysis of superconducting fault current limiter for stabilization of synchronous generators in multimachine system: A two‐machine infinite bus system

This paper presents the results of analyses of the effectiveness of a superconducting fault current limiter (SFCL) to stabilize the synchronous generators, suppress turbine shaft torque oscillations, and limit the fault current in a two‐machine infinite bus system. In this study, the system model with two SFCLs having shunt resistance installed at each generator terminal was used taking 3LG (three lines to ground) fault at 12 fault points into account. These analyses were performed using EMTP/ATP. It is found that the use of SFCL with a shunt resistance value of 1.1 pu is most effective for all fault points for the stabilization of synchronous generators, the suppression of turbine shaft torque oscillations, and the limitation of fault current. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(3): 44–53, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10272     

含分布式电源的配电网故障分析的解耦相分量法

分布式发电系统的接入改变了配电系统的故障电流分布,传统的配电网故障分析方法已经不能满足未来分布式发电系统的需求.针对含分布式电源的配电网故障分析开展研究,提出了合分布式电源的配电网故障分析计算的解耦相分量法.将含有分布式电源的配电网分解成"梯形"网络和"辐射状"网络,选择短路点为边界节点,借助于相序参数变换技术,通过三相解耦等值电路计算故障点短路电流,并利用支路电流分流系数计算任意节点电压.所提算法无需形成配电网节点复数导纳或阻抗参数矩阵;可以精确地模拟故障;可方便地计及短路点接触电阻的影响;避免了复杂的序网连接.采用20节点算例对所提方法进行了测试,算例结果证明了该算法的可行性和有效性.     

孤岛微网并联逆变器环流抑制与母线电压控制

针对孤岛微网中采用传统下垂控制的并联微源逆变器之间存在较大环流及母线电压和频率偏移问题,文中从环流的一般性定义出发,分析了环流与负荷功率分配之间的定量关系,在此基础上将环流抑制问题转化为功率精确分配问题,并提出了一种母线电压和频率自恢复的改进鲁棒下垂控制方法.将PI控制器引入无功电压控制环中,实现无功功率的精确分配并加...     

10 kV配电网合环电流暂态过程的分析与仿真

分析了配电网合环暂态过程及合环冲击电流对电网安全运行的影响.结合配电网特点建立了数学模型,推导出了合环冲击电流的数学表达式,并应用PSCAD/EMTDC软件对实际算例进行了暂态仿真计算.仿真计算结果表明,建立的数学模型正确可行.