Comparison study of harmonic imaging （HI） and fundamental imaging （FI） in fetal echocardiography

Objectives: To directly compare the quality of harmonic imaging (HI) and fundamental imaging (FI) in fetal echocardiography and to determine any differences in image quality between the two m0dalities. Methods : Fetal echocardiograms were performed with the use of FI and HI in 58 fetuses, image quality and vi-sualization of left and right atria, left and right ventricles, mitral and tricuspid valves, aortic and pulmonary valves, left and right ventricular outflow tracts were evaluated and compared between FI and HI. Results :Mean HI scores were higher than mean FI scores (2.73±0.43 vs 2.16±0.69, P <0.001)for all the card-iovascular structures evaluated. Compared with FI, HI improved the image quality and visualization of fetal cardiac structures in subjects with both good (2.73±0.43 vs 2.88±0.32, P < 0.001) and suboptimal (1.65±0.41 vs 2.58±0.47, P < 0.001) echocardiographic windows. The interobserver correlation coefficient for the grading scores was 0.74 ( P < 0. 001 ) . Conclusions: harmonic imaging enhances and improves the im-age quality of fetal echocardiography ; and has important potential role in cardiac imaging in the fetus.

Design optimization of 3.9GHz fundamental power coupler for the SHINE project

The third harmonic superconducting cryomodule is being designed for the Shanghai High repetition rate XFEL and Extreme light facility(SHINE)project,which is under construction.In contrast to the European X-ray Free Electron Laser(E-XFEL)project,the 3.9 GHz cryomodules in the SHINE project will operate in the continuous wave regime with higher radio frequency average power for both cavities and couplers.We propose a 3.9 GHz fundamental power coupler with an adjustable antenna length,for satisfying the SHINE project requirements.Here,we describe the 3.9 GHz fundamental power coupler's design considerations and power requirements for various operating modes of the SHINE Linac.We also present the results of the radio frequency simulation and optimization,including the studies on multipacting and thermal analysis of the proposed 3.9 GHz coupler.

Two-Colour Effect on the Ionization and Harmonic Generation of One-Dimensional He^(+)

Using the one-demensional ion mode,We theoretically investigate the dynamics ionization process and the high-order harmonic generation of the He^(+)subject to different kinds of two-colour laser pulse with the same fundamental frequency but various harmonic frequencies.It is found that from the results calculated by numerically solving the time-dependent Schrödinger equation,the two-colour laser pulse with the fundamental frequency and harmonic frequency enables the power spectrum of high-order harmonic generation to increase by a few orders of magnitude and the yield of He^(+)to enhance significantly when the harmonic frequency of laser pulse is close to the energy interval between the ground state and the first excited state of He^(+);even the harmonic field added into the pulse is much weaker than the fundamental one.

Harmonic Minimization in Seven Level Cascaded Multilevel Inverter Using Selective Harmonic Elimination PWM Techniques

This paper concentrates on enhancing the productivity of the multilevel inverter and nature of yield voltage waveform. Seven level lessened switches topology has been actualized with just seven switches. Essential Switching plan and Selective Harmonics Elimination were executed to diminish the Total Harmonics Distortion (THD) esteem. Selective Harmonics Elimination Stepped Waveform (SHESW) strategy is executed to dispense with the lower order harmonics. Fundamental switching plan is utilized to control the switches in the inverter. The proposed topology is reasonable for any number of levels. The harmonic lessening is accomplished by selecting fitting switching angles. It indicates would like to decrease starting expense and unpredictability consequently it is able for modern applications. In this paper, third and fifth level harmonics have been disposed of. Simulation work is done utilizing the MATLAB/Simulink programming results have been displayed to accept the hypothesis.

输入电压波动下变模态宽增益谐振变换器研究

针对传统LLC谐振变换器在宽输入下开关损耗过大、增益范围较窄、难以保持输出稳定的问题,研究一种变模态宽增益谐振变换器。该变换器及其控制策略能够依据输入电压的大小,在全桥和半桥两种模态之间自由切换,有效拓宽电压增益范围。通过对变换器谐振腔结构的优化,进一步拓宽增益,减小能量循环、降低开关管损耗,同时能够在电流传输中引入三次谐波,降低损耗。利用基波近似法对电压增益进行推导,绘制增益曲线图,分析谐振参数对电压增益的影响,根据需求设计合适的参数,并运用变频控制,通过调节输入电压,使得变换器运行在不同模态,实现电压平稳输出。搭建一台55~220 V输入、30 V输出的300 W实验样机,实验结果证明了所提变换器控制策略的有效性。

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。

考虑整流性负载特性的LCC-S型无线电能传输系统优化设计

无线电能传输系统中的整流性负载具有非线性特征,而对系统传输特性分析和谐振参数设计时常采用基波分析法,将整流性负载等效为纯电阻,导致理论分析与实际存在一定偏差、系统偏离谐振状态。针对该问题,以LCC-S型无线电能传输系统为研究对象,考虑谐波以及整流性负载的非线性,对系统传输特性进行分析,进而提出基于整流性负载补偿的负载阻抗和接收端串联谐振电容参数的计算方法,并对逆变电路开关特性进行分析验证。所提接收端谐振参数设计方法能够使系统接收端回路谐振,提高系统的输出功率;降低逆变电路开关管的关断电流,提升系统的传输效率。搭建了一套2.5 kW的LCC-S型无线电能传输实验平台,验证了理论分析与所提参数设计方法的有效性和正确性。

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DSOGI-PLL与ANF-LPF的i_(p)-i_(q)三相谐波检测方法

随着分布式电源大规模接入电网,电力系统中频率波动、电压不平衡以及谐波畸变等问题日益严重。在这样不平衡和失真的电网条件下,传统i_(p)-i_(q)谐波检测法已不能满足工程需要。为解决这一问题,文中提出一种基于DSOGI-PLL与ANF-LPF的i_(p)-i_(q)三相谐波检测方法。一方面,采用DSOGI-PLL提高复杂电网下提取基波相位的能力;另一方面,采用一种具有选择性谐波滤波能力的改进结构LPF,来提高谐波检测的抗干扰能力。结果表明,所提方法能够在复杂电网条件下完成三相谐波检测。

换流变压器铁心夹件接地电流谐波特性分析

为了解决仅依据接地电流的全电流值无法准确有效判断换流变压器的检修状态问题,以及更深入探究换流变压器铁心、夹件接地电流的特性,采用汉宁窗插值快速傅里叶变换算法对采样信号进行谐波分析,得到接地电流基波和2~50次谐波的幅值及含有率。对比分析基波与全电流的变化趋势,以及不同时刻接地电流的全电流、基波、谐波数据,得到谐波幅值变化幅度,进一步揭示换流变压器铁心、夹件接地电流值过大和跳动的问题,为判断换流变压器铁心、夹件接地电流状态与变压器运行状况提供新的思路。

Mathematical Wave Functions and 3D Finite Element Modelling of the Electron and Positron

The wave/particle duality of particles in Physics is well known. Particles have properties that uniquely characterize them from one another, such as mass, charge and spin. Charged particles have associated Electric and Magnetic fields. Also, every moving particle has a De Broglie wavelength determined by its mass and velocity. This paper shows that all of these properties of a particle can be derived from a single wave function equation for that particle. Wave functions for the Electron and the Positron are presented and principles are provided that can be used to calculate the wave functions of all the fundamental particles in Physics. Fundamental particles such as electrons and positrons are considered to be point particles in the Standard Model of Physics and are not considered to have a structure. This paper demonstrates that they do indeed have structure and that this structure extends into the space around the particle’s center (in fact, they have infinite extent), but with rapidly diminishing energy density with the distance from that center. The particles are formed from Electromagnetic standing waves, which are stable solutions to the Schrödinger and Classical wave equations. This stable structure therefore accounts for both the wave and particle nature of these particles. In fact, all of their properties such as mass, spin and electric charge, can be accounted for from this structure. These particle properties appear to originate from a single point at the center of the wave function structure, in the same sort of way that the Shell theorem of gravity causes the gravity of a body to appear to all originate from a central point. This paper represents the first two fully characterized fundamental particles, with a complete description of their structure and properties, built up from the underlying Electromagnetic waves that comprise these and all fundamental particles.

无线电能传输系统谐波分析

基波近似法(FHA)在松耦合无线电能传输(WPT)系统中得到了广泛的应用。然而,由于强耦合系统中存在高次谐波分量,FHA会影响分析精度,因此提出了强耦合WPT系统的精确分析方法,推导了考虑谐波分量贡献的输出表达式。仿真和实验结果均验证了该方法的有效性。

六相全桥逆变器驱动PMSM的简化模型预测电流控制

全桥逆变器电机驱动或称开绕组结构虽然兼具相间电气隔离、容错性能好及器件开关频率低等优点,但存在逆变器输出电压矢量多、冗余严重且控制约束等问题。文中以共直流母线供电的六相全桥逆变器驱动六相永磁同步电机为研究对象,提出了一种基于二级矢量优化的简化模型预测电流控制算法,在实现电机定子基波电流有效跟踪控制的同时有效抑制了定子电流的谐波及零序分量。文中基于矢量空间解耦理论对六相全桥逆变器的输出电压矢量进行了分层分析,以定子基波电流控制、谐波及零序电流抑制为准则对逆变器输出的729个电压矢量进行二级优化,得到候选的12个电压矢量,以此为基础设计了模型预测电流控制算法。实验结果表明,该简化模型预测电流控制方法具有良好的动静态性能,能在基波电流控制的同时有效抑制谐波及零序电流分量,可为多相电机驱动系统研究提供一定的理论支撑。

Normalized estimation of fundamental frequency and measurement of harmonics/interharmonics

An adaptive notch filter is presented to estimate the fundamental frequency and measure both harmonics and interharmonics of an almost periodic signal with unknown time-variant fundamental frequency, which has the ro- bustness that the convergence speed is determined by neither amplitude nor frequency of fundamental component. The algorithm forms a one-dimensional slow adaptive integral manifold whose existence and stability are proved by averaging method and Lyapunov stability theorem. The local exponential stability and the ultimate boundedness of fundamental fre- quency estimation are proved. The local exponential stability makes sure that the fundamental frequency, the harmonic and interharmonic components can be all fast tracked. The principle for adjusting the parameters with their influences on tran- sient and steady-state performance is investigated and decreasing parameters can improve noise characteristic. The validity is verified by simulation results.

HARMONIC MAPS AND FUNDAMENTAL GROUPS OF NONPOSITIVELY CURVEDRIEMANNIAN MANIFOLDS

Using the theory of harmonic maps the authors discuss theproperties of the fundamental group of a complete nonpositivelycurved Riemannian manifold, and prove that the finitely generatedvirtual solvable subgroup of fundamental group of a completenonpositively curved Riemannian manifold either is a peripheralsubgroup of fundamental group or can be realized by animmersed totall geodesic closed flat manifold. It generalizessome results of Gromoll-Wolf, Lawson-Yan and Schoen-Yau.

高效率双频连续F类功率放大器的设计

为满足多标准和多频段无线通信的需求,针对特定频段如何提高效率问题,基于连续F类功放的谐波控制理论,提出了一种高达三次谐波控制的双频功放设计方法,实现了两个频段的高效率性能。首先,分析了电流源平面的各次谐波阻抗,基于连续F类阻抗设计空间的灵活性,设计的双频谐波控制网络将二次谐波控制在短路点附近,同时将三次谐波控制在开路点附近,可提高任意两个频段功放的效率。随后,针对传统耦合器基频匹配网络在多频匹配方面的不足,提出了改进的双频阻抗匹配网络,简化了匹配方法并实现了不同频点的最佳基波阻抗同时匹配到标准的50Ω。最后,使用Cree公司的CGH40010F GaN HEMT设计了一款工作在1.8和2.6 GHz的双频连续F类功率放大器,并进行测试,结果显示在1.8和2.6 GHz的饱和输出功率分别为40.6 dBm和39.5 dBm,最大功率附加效率分别为75.4%和74%,最大漏级效率均大于75%。测试结果表明,所提出的双频谐波控制网络设计方法在提高功放效率方面具有显著优势。

削弱表贴式永磁电机2p阶径向电磁力波幅值的磁极设计方法

电磁振动是影响电机性能的主要因素之一,针对瓦片形磁极永磁电机2 p阶径向电磁力波引起的电磁振动,提出优化磁极参数的方法用以改变高阶磁密谐波相位和幅值,进一步削弱2 p阶径向电磁力波幅值。根据径向磁密解析表达式,推导出2 p阶径向电磁力波与磁极参数的函数关系,分析各磁极参数对气隙磁密和2 p阶径向电磁力波的影响;进一步求得使2 p阶径向电磁力波幅值最小化的目标函数,并用内点法得到优化的磁极结构参数,对比分析优化前后有限元计算的电磁性能和2 p阶处的振动响应。结果表明,该优化设计磁极的方法可在不降低电机性能的同时,抑制2 p阶径向电磁力波引起的电磁振动。

输入电压波动下宽增益谐振变换器优化设计

该文设计了一种全桥-半桥模态切换的宽增益谐振变换器:首先,通过优化谐振腔结构,在电流传输中引入三次谐波,减小能量循环及开关管损耗;然后,根据输入电压控制变换器在两种不同模态切换,拓宽增益范围,使得变换器具有更灵活的调压特性;最后,利用基波近似法推导电压增益并绘制增益曲线仿真图,分析谐振参数对电压增益的影响并设计合适的参数,运用变频控制优化输出波形,实现变换器在不同模态下的电压平稳输出。通过搭建实验样机展开实验分析,结果显示不同模态下变换器均能实现软开关,增益拓宽且输出效率明显提升。

应用于5G通信的三频F类功率放大器设计

为满足5G通信技术的多标准和多频段需求,针对如何提高多频段效率的问题,提出了一种三次谐波控制的三频功率放大器设计方法。首先基于F类功率放大器的原理设计了三频谐波控制网络,用于提高三频功率放大器效率;然后又给出了一种三频基波匹配方法,用来实现任意三频的基波匹配并简化输出匹配结构;最后设计了一款高效率的三频F类功率放大器并进行测试,测试结果表明该功率放大器在1.8、2.6和3.4 GHz的漏级效率分别为74.2%、73.8%和69.0%,饱和输出功率均在40 dBm左右,增益也可达到14.5 dB。

一种新型级联CDSOGI-PLL的电网电压同步信号检测技术

基于双二阶广义积分器的锁相环DSOGI-PLL在电网电压含有大量低次谐波时,其滤波效果不理想,锁相环提取的同步信号频率出现波动。在DSOGI-PLL的基础上,提出一种新型的级联锁相环结构CDSOGI-PLL(cascade second-order generalized integrator PLL)。该结构利用级联的SOGI模块同时削弱电网电压中的各次谐波和间谐波,从而减少谐波对锁相环的影响,准确地提取电网电压同步信号。Matlab仿真和实验结果均表明,文中提出的新型CDSOGI-PLL在电网电压不对称和含有大量低次谐波时能有效、准确地提取基波的正序分量、频率和相位。