A Liability Division Method for Harmonic Pollution Based on Line-Transferred Power Components

The existing liability division methods for harmonic pollution are either inexplicit or incomplete in physical meaning. To compensate these defects, two new methods are proposed based on line-transferred power components in this paper. At first, all harmonic sources are represented by ideal equivalent current source, line current components and bus voltage components of a source are determined by stimulation of this source with all other sources disabled. Then, the line-trans- ferred power component owing to a source under all sources action together is determined by the theory of line-transferred power components, and called source’s line-transferred power component. At last, the liability of a source for line-end harmonic pollution is divided by two methods: the ration of the source’s line-transferred active power component to the total line-transferred power, and the ration of projection of the source’s line-transferred complex power component to absolute value of the total line-transferred complex power. These two methods are taken into account not only harmonic voltage but also harmonic current in the liability division. Simulation results show that the proposed liability division method based on active power component is the most effective and ideal one.

Coordinated Control of Second-order Harmonic Voltage and Current Fluctuations in Cascaded H-bridge Inverter with Supercapacitor and DC-DC Stage at Variable Output Frequencies

In the cascaded H-bridge inverter(CHBI)with supercapacitor and dc-dc stage,inherent second-order harmonic power flows through each submodule(SM),causing fluctuations in both the dc-link voltage and the dc-dc current.There exist limitations in handling these fluctuations at variable output frequencies when employing proportional-integral(PI)control to the dc-dc stage.This paper aims to coordinately control these second-order harmonic voltage and current fluctuations in the CHBI.The presented method configures a specific second-order harmonic voltage reference,equipped with a maximum voltage fluctuation constraint and a suitable phase,for the dc-dc stage.A PI-resonant controller is used to track the configured reference.This allows for regulating the second-order harmonic fluctuation in the average dc-link voltage among the SMs within a certain value.Importantly,the second-order harmonic fluctuation in the dc-dc current can also be reduced.Simulation and experimental results demonstrate the effectiveness of the presented method.

Robust Blind Separation for MIMO Systems against Channel Mismatch Using Second-Order Cone Programming

To improve the deteriorated capacity gain and source recovery performance due to channel mismatch problem,this paper reports a research about blind separation method against channel mismatch in multiple-input multiple-output(MIMO) systems.The channel mismatch problem can be described as a channel with bounded fluctuant errors due to channel distortion or channel estimation errors.The problem of blind signal separation/extraction with channel mismatch is formulated as a cost function of blind source separation(BSS) subject to the second-order cone constraint,which can be called as second-order cone programing optimization problem.Then the resulting cost function is solved by approximate negentropy maximization using quasi-Newton iterative methods for blind separation/extraction source signals.Theoretical analysis demonstrates that the proposed algorithm has low computational complexity and improved performance advantages.Simulation results verify that the capacity gain and bit error rate(BER) performance of the proposed blind separation method is superior to those of the existing methods in MIMO systems with channel mismatch problem.

Establishment of Numerical Wave Flume Based on the Second-Order Wave-Maker Theory

With growing computational power, the first-order wave-maker theory has become well established and is widely used for numerical wave flumes. However, existing numerical models based on the first-order wave-maker theory lose accuracy as nonlinear effects become prominent. Because spurious harmonic waves and primary waves have different propagation velocities, waves simulated by using the first-order wave-maker theory have an unstable wave profile. In this paper, a numerical wave flume with a piston-type wave-maker based on the second-order wave-maker theory has been established. Dynamic mesh technique was developed. The boundary treatment for irregular wave simulation was specially dealt with. Comparisons of the free-surface elevations using the first-order and second-order wave-maker theory prove that second-order wave-maker theory can generate stable wave profiles in both the spatial and time domains. Harmonic analysis and spectral analysis were used to prove the superiority of the second-order wave-maker theory from other two aspects. To simulate irregular waves, the numerical flume was improved to solve the problem of the water depth variation due to low-frequency motion of the wave board. In summary, the new numerical flume using the second-order wave-maker theory can guarantee the accuracy of waves by adding an extra motion of the wave board. The boundary treatment method can provide a reference for the improvement of nonlinear numerical flume.

Surface second harmonic generation of chiral molecules using three-coupled-oscillator model

Based on the three-coupled-oscillator molecular model we proposed, the relation between the second-order susceptibilities of a chiral film and the molecular hyperpolarizabilities is given. The effect of microscopic parameters on the second-order susceptibilities is simulated numerically and the difference between the efficiencies of s-polarized secondharmonic fields induced by the left- and the right-handed circularly-polarized fundamental beams is discussed. The theoretical basis for studying second-order nonlinear optical properties of the chiral molecular media with a tripod-like structure is provided in this paper.

Design and Analysis of Cascaded Hybrid-Bridge Multi-Cell Multilevel Inverter with Reduced Total Harmonic Distortion Profile

This multilevel inverter methodology is the center of focus among researchers in recent era.It has been focused due to its advantages over existing topologies,drawbacks and improvement of power quality,Multi-level inverter has the ability to generate nearly sinusoidal waves.This sinusoidal wave can be further improved by increasing the level of output voltage or with the help of filter design,and this manuscript presents single-phase Multi cell Multi-Level Inverter(MLI).It has been considered for reducing component count to get a higher number of output voltage levels and lower Total harmonics distortion profile.It comprises with four symmetric DC input voltage and 10 IGBT switches to produces stepped output of 9 level,and when deploy asymmetric Dc voltage source the same circuit will produce 31 level output with some changes in firing scheme,moreover this circuit is the family of cascaded hybrid bridge inverter so this circuit covered advantage of CHB MLI,This circuit uses lower no.of switch as compared to existing conventional MLIs such as FC-MLI,CHB-MLI,NPC-MLI,This paper also provides one of most pertinent controls and modulation mechanisms for a MLI using a hybrid reference/carrier-oriented sinusoidal PWM mechanism.At last,simulated outcomes are to validate the performance of both architectures in MLI structure as well as verify the concept.

A novel control scheme for simultaneous elimination of imbalance, disturbance and voltage harmonic in power systems

In recent years, the increasing application of nonlinear and unbalanced electronic equipment and large single phase loads have made voltage imbalance a serious problem in power distribution systems. A novel approach has been proposed to eliminate voltage imbalance and disturbances. The main strategy of this scheme is based on series active filter. By improving control circuit toward existing schemes and proposing a new strategy to control the voltage amplitude, simultaneous elimination of voltage imbalance, faults, voltage harmonics and also compensation of voltage drop in transmission lines become possible. Eventually, the voltage on the load side is a perfectly balanced three phase voltage with specific proper amplitude. The proposed scheme has been simulated in a test network and the results show high capability of this scheme for the complete elimination of imbalance without phase shift.

A New Topology for a Single Phase Multilevel Voltage Source Inverter with Reduced Number of Components

Multilevel inverters have gained much attention for its operation involving applications ranging values of high power rating. This paper proposes a switching topology for asymmetric multilevel inverter utilizing less number of power electronics components. When the number of the output level increases, it requires more switching states and eventually the number of switching components. The increased number of switches results in higher switching losses which may lead to power loss, and reduction of efficiency of the overall conversion system. The salient feature of this proposed topology is that the module can be used as a sub multiple level structure and can be extended for any number of level with minimal increase in the switching components.

Enhancement of second-order harmonic generation in polarized BaTiO_3 thin films embedded with Ag nanoparticles

RECENTLY, much attention has been paid to optical properties of ferroelectric thin films. Be-

基于一种新型正弦幅值积分器的谐波检测方法

针对基于瞬时无功理论的ip-iq谐波检测法结构复杂、响应速度慢等问题,提出了一种采用改进正弦幅值积分器结构的谐波电流检测方法。首先,利用二阶广义积分器的输出滤波特性及正弦幅值积分器的极性选择特性,使其相结合构造出了一种滤波性能更强,同时具有频率及极性选择作用的新型积分器。然后,利用该积分器快速准确地提取基波正序分量,并有效应用于谐波检测环节中。当电网电压存在直流偏置问题时,该积分器所构造的锁相环也能准确锁定电网频率及相位信息。最后,理论分析及仿真实验结果表明:该方法无需进行瞬时对称分量分离,就可提取出电网电压及负载电流基波的正负序分量,计算量小,谐波检测更精确。

基于实测数据的牵引供电系统并联谐波谐振概率识别方法

当前,我国高速铁路电力机车广泛采用脉冲宽度调制的四象限变流器,在其性能改善的同时也带来了频带更宽的高次谐波问题,更易激发牵引供电系统谐波谐振。谐波谐振可能会引起过电压/过电流,严重时引发设备爆炸、保护误动等安全事故。因此,准确识别系统潜在的谐振频率具有重要意义。目前常用的频率扫描分析、谐振模态分析等方法依赖于系统拓扑和模型的精确性,而基于实测数据的传统识别方法的准确性受系统参数波动和背景谐波影响较大。为此,提出了一种基于实测数据的牵引供电系统并联谐振概率识别方法,以电压、电流波形的余弦相似度作为谐振预判条件以减少无效计算,并综合基波/谐波功率因数、系统谐波阻抗幅值等多层次谐振特征进行概率分析,克服了系统参数波动和背景谐波影响。仿真研究、实测数据分析与已有研究方法对比,表明所提方法在负荷波动性强、背景谐波较大时仍然适用,且识别的准确性更高,验证了该方法的有效性和可靠性。

新能源场站高比例接入下主流类型工频量距离保护比对

新能源场站高比例接入电网后,已有广泛应用的工频量距离保护判据存在无法准确识别电网故障的问题。文章着重从装置中保护判据与工频量提取算法入手,对比分析新能源场站高比例接入场景下不同类型距离保护算法的适应性。针对保护判据,对比分析了方向圆、多边形、比相式以及工频变化量距离保护各自的适应性,明确了能够较好适用于新能源场站高比例接入的距离保护判据。针对工频量提取算法,探究了不同类型新能源场站所提供短路电流中非周期谐波量的变化特性,进一步推导了受谐波量影响的傅里叶算法对工频量提取产生的计算误差,确定了影响工频量提取精度的关键谐波分量。

基于时间调制技术的可重构后向散射通信系统

近年来,时间调制阵列因其优越的矢量调控性能受到广泛关注。基于时间调制方法,该文提出一种可重构后向散射通信系统。该系统中后向散射节点将多类数字调制符号映射至控制信号波形的谐波分量中,以该波形控制后向散射节点对基站端来波的散射与吸收态;接收机采样后向散射信号并提取控制信号波形后,通过傅里叶变换计算谐波分量并恢复后向散射节点发射的数字调制符号。仿真结果验证了几种谐波解调方法的性能及与理论值的一致性。基于幅度、相位键控及正交振幅调制的可重构后向散射传输实验验证了所提系统和方法的可行性。相比较而言,该后向散射通信系统具有功耗低、结构简单、多类数字调制方式可重构的特点。

实际工况下机车牵引变压器铁心损耗模型建立与验证

为实现电力机车牵引变压器的精细化设计,降低产品设计中的冗余量,提高产品的效率减小体积,需要准确预估机车牵引变压器在实际工况下的损耗特性。本文首先模拟牵引变压器实际工作状态,对谐波交变磁化下牵引变压器用电工材料电磁特性的模拟展开研究工作。通过测量牵引变压器实际工作时的电磁特性曲线,分析铁心材料的电磁特性。然后通过对磁化角度和谐波次数的非线性关系研究,建立基于损耗模型系数的磁化角度变系数方程,提出谐波损耗非线性修正系数,进而提高机车牵引变压器损耗模型计算精度。

基于误差函数相位偏移的电场式时栅角位移传感器自标定

比对标定对于传感器测量精度的保持和提升具有重要意义,但其易受现场环境限制,且成本昂贵。电场式时栅精度不断刷新,寻找外部参考基准也变得日益困难。针对这一难题,提出了以圆周封闭原则为基准,利用傅里叶级数的平移定律,将电场式时栅的误差序列值以2π/n角位移值进行移相,利用具有不同移相次数的误差序列值进行频谱分析,互相补偿缺失的谐波分量,最终利用各次谐波分量重构传感器误差函数的自标定方法。并据此设计、搭建了相应的自标定实验平台。实验结果表明,该自标定方法对于电场式时栅角位移传感器中所包含的周期性误差补偿效果显著。对极内,使用该自标定方法与用光栅作为参考基准所获得的标定精度基本相当,两者误差为0.05",对极内误差下降67%;整周范围内,两者误差为0.15",整周误差下降80%。该自标定方法相比于传统的比对标定法在效率、应用范围及标定成本方面均拥有显著优势。

负荷不对称工况发电机定子电磁力与振动特性

为了研究电力系统中负荷不对称引起的发电机磁场畸变和振动加剧问题,针对三相不对称电流产生的负序电流,首先利用对称分量法推导出各序电枢磁动势,同时考虑励磁电流直流分量和偶倍频交流分量产生的磁动势,利用麦克斯韦应力张量法推导径向电磁力密度表达式,通过二维傅里叶分解得到电磁力密度谐波,获取电磁力密度的时间和空间谐波特征。以一台QFSN-300-2型汽轮发电机为例,仿真验证了负荷不对称工况发电机电磁力特征谐波的存在,分析得出其中两类幅值极大的新电磁力谐波为该故障下振动加剧的原因,评估了谐波对定子铁心振动和振型的影响,得出定子四倍频和六倍频振动增大的结论,对长期工作在负荷不对称状态下发电机组的气隙电磁力理论研究和振动减缓有指导意义。

基于对称分量法的混合型电力有源滤波器研究

针对光伏并网发电系统中非线性负载带来的谐波问题,以及大量单相非线性负载接入后的三相电力系统严重不对称情况,提出一种新型混合型滤波器主电路结构和基于应用改进的对称分量法的有源滤波器控制方法。首先,建立混合型滤波器的主电路结构,分析有源部分的拓扑结构和无源部分的工作模式及零序电抗。接着,给出该滤波器的锁相环控制电路以及整体硬件控制结构。针对三相负载严重不对称情况,采用改进对称分量法精确提取中线侧零序电流分量,实现滤波器有源部分的控制。最后,通过仿真验证与现场应用,验证了该混合型滤波器及控制方法在三相负载对称和严重不对称情况下的有效性,结果表明其具有明显的滤波效果及较优的经济性。

原子结构中的z轴是特殊轴吗?

通过对量子态空间、基函数、幺正变换等量子力学基本概念的介绍,阐释了原子结构中z轴表现出特殊性的原因,明确了在球对称的原子结构中,任何方向都不具有特殊性,z轴表观的特殊性主要源自人们选择了特定基函数来描述原子中电子的运动行为。

电力系统中压电网谐振关键元器件评估

模态分析法可以获得最丰富的谐振信息,现有灵敏度分析方法可以得到每种元器件对谐振影响程度的排序,但无法明确辨别谐振关键元件和谐振电路。首先,通过推导对各参与因子的物理意义进行了解释,归纳了现有的2种灵敏度分析方法;然后,考虑不同属性元器件取值范围的差异性及逆变器外特性的影响,提出了一种适用于配电网谐振关键元件和电路的识别方法;最后,通过算例分析和PSCAD仿真结果,验证了所得谐振关键元器件的准确性。该方法可以较为准确地识别出系统固有谐振的关键元器件,为研究谐波谐振问题及其抑制、事故调查分析等提供参考。

基于模糊神经网络的配电网短路故障自动化识别系统

为解决快速、准确地识别和定位配电网中短路故障的问题,设计基于模糊神经网络的配电网短路故障自动化识别系统。通过获取的零序电流的稳态基波分量和五次谐波分量,建立模糊神经网络配电网短路故障自动化识别模型;利用映射、生成隶属度函数,并进行模糊推理和归一化处理,输出识别结果。实验表明,当并发用户数达到550个时,系统预留空间维持在43%,超过预设阈值,确保了系统稳定运行。该系统能有效采集配电网线路的零序电流并分离其分量,同时准确识别A相接地短路和BC相间短路故障,应用效果显著。