Application of the method of equivalent edge currents to composite scattering from the cone-cylinder above a dielectric rough sea surface

Compared with scattering from a rough surface only, composite scattering from a target above a rough surface has become so practical that it is a subject of great interest. At present, this problem has been solved by some numerical methods which will produce an enormous calculation amount. In order to overcome this shortcoming, the reciprocity theorem （RT） and the method of equivalent edge currents （MEC） are used in this paper. Due to the advantage of RT, the difficulty in computing the secondary scattered fields is reduced. Simultaneously, MEC, a high-frequency method with edge diffraction considered, is used to calculate the scattered field from the cone-cylinder target with a high accuracy and efficiency. The backscattered field and the polarization currents of the rough sea surface are evaluated by the Kirchhoff approximation （KA） method and physical optics （PO） method, respectively. The effects of the backscattering radar cross section （RCS） and the Doppler spectrum on the size of the target and the windspeed of the sea surface for different incident angles are analysed in detail.

Validity and Accuracy of Eddy Current Field Analysis of Laminations by Introducing Equivalent Conductivities

对于分析叠片铁心中的涡流问题，利用各种等效电导率替代硅钢片实际电导率的匀质化方法是很有应用前景的。为了评估各种电导率模型，该文提出了铁心涡流场分析的二维解析验证方法，并分别基于引入各向异性或各向同性等效电导率的铁心连续体表述和实际叠片表述对涡流场进行了解析计算。通过比较连续体表述下所得到的平均磁通密度和涡流损耗值与相应由实际叠片表述所得到的精确解，对各种电导率模型的有效性和准确性在各种条件下进行了评估。为了进一步考察电导率模型对实际工程问题的适用性，利用有限元法进行了关于TEAM21面向工程基准问题的磁通和杂散场损耗计算。计算结果表明，由该文作者所提出的等效电导率模型优于其他模型。

Research on the Equivalence Between Double Differential- mode Current Injection and Radiation Test Method

There are the application scope limits for single differential-mode current injection test method, so in order to carry out injection susceptibility test for two-pieces equipment interconnected with both ends of a cable simultaneously, a double differential-mode current in- jection test method (DDMCI) is proposed. The method adopted the equivalence source wave theorem and Baum-Liu-Tesche(BLT) equation as its theory foundation. The equivalent corresponding relation between injection voltage and radiation electric field intensity is derived, and the phase relation between the two injection voltage sources is confirmed. The results indicate that the amplitude and phase of the equivalent injection voltage source is closely related to the S parameter of directional coupling device, the transmission line length, and the source vector in BLT equation, but has nothing to do with the reflection coefficient between the two equipment pieces. Therefore, by choosing the right amplitude and phase of the double injection voltage sources, the DDMCI test is equivalent to the radiation test for two interconnected equipment of a system.

Equivalent magnetic dipole method used to design gradient coil for unilateral magnetic resonance imaging

The conventional magnetic resonance imaging(MRI)equipment cannot measure large volume samples nondestructively in the engineering site for its heavy weight and closed structure.In order to realize the mobile MRI,this study focuses on the design of gradient coil of unilateral magnet.The unilateral MRI system is used to image the local area above the magnet.The current density distribution of the gradient coil cannot be used as a series of superconducting nuclear magnetic resonance gradient coils,because the region of interest(ROI)and the wiring area of the unilateral magnet are both cylindrical side arc surfaces.Therefore,the equivalent magnetic dipole method is used to design the gradient coil,and the algorithm is improved for the special case of the wiring area and the ROI,so the X and Y gradient coils are designed.Finally,a flexible printed circuit board(PCB)is used to fabricate the gradient coil,and the magnetic field distribution of the ROI is measured by a Gauss meter,and the measured results match with the simulation results.The gradient linearities of x and y coils are 2.82%and 3.56%,respectively,less than 5%of the commercial gradient coil requirement.

MoM-PO-MEC混合法及其在组合体散射中的应用

对于携带电小结构的电大目标的散射问题,单纯的矩量法(MoM)或单纯的物理光学法(PO)由于自身固有的缺点,都不能给出有效的结果.而矩量法与物理光学法的混合方法是解决此类问题的有效途径,本文在MoM-PO混合法的基础上,通过引入等效电磁流方法(MEC)来计算PO区域边缘的绕射贡献,提出了一种MoM-PO-MEC混合方法,并将其计算结果与多层快速多极子计算结果进行比较,最终证明了该混合方法的有效性。

Improved method to derive equivalent current systems from global MHD simulations

Derivation of equivalent current systems(ECS)from a global magnetospheric magnetohydrodynamics(MHD)model is very useful in studying magnetosphere-ionosphere coupling,ground induction effects,and space weather forecast.In this study we introduce an improved method to derive the ECS from a global MHD model,which takes account of the obliqueness of the magnetic field lines.By comparing the ECS derived from this improved method and the previous method,we find that the main characteristics of the ECS derived from the two methods are generally consistent with each other,but the eastward-westward component of the geomagnetic perturbation calculated from the ECS derived from the improved method is much stronger than that from the previous method.We then compare the geomagnetic perturbation as a function of the interplanetary magnetic field(IMF)clock angle calculated from the ECS derived from both methods with the observations.The comparison indicates that the improved method can improve the performance of the simulation.Furthermore,it is found that the incomplete counterbalance of the geomagnetic effect produced by the ionospheric poloidal current and field-aligned current(FAC)contributes to most of the eastward-westward component of geomagnetic perturbation.

A study on the multi-componentsubstrom current

A new technique of eigen mode analysis, Method of Natural Orthogonal Components (MNOC) is used to analyze the ionospheric equivalent current systems obtained on the basis of magnetic data at six meridian magnetometer chains in the northern hemisphere during March 17 19, 1978. The results show that the whole current pattern for any given instant consists of a few eigen modes with different intensities. The first eigen mode exhibits a two cell current construction, characterizing the large scale magnetospheric convection and directly driven process, while the second eigen mode shows a concentrated westward electrojet at midnight sector, characterizing the substorm current wedge and the loading unloading process. The first mode consistently exists whenever during quiet periods or at substorms, and its intensity increases from the beginning of the growth phase of substorms, then quickly intensifies in the expansion phase, followed by a gradual decrease in the recovery phase. On the other hand, the intensity of the second mode remains to be near zero during both quiet time and the growth phase of substorms. Its rapid enhancement occurs in the expansion phase. These characteristics in the current patterns and the intensity variations coincide with the defined physical processes of the directly driven and loading unloading components.

考虑精确磁通的电磁加载装置等效磁路建模

为提高电磁加载装置在控制应用时的模型预测快速性与精确性,考虑电磁加载装置硅钢片表面涡流磁场生成因素与不同轴偏心下有效气隙长度,采用非线性方程拟合硅钢片磁化曲线,建立包含磁极边缘效应、磁极铁心、转子硅钢片动态磁阻与涡流磁场的电磁加载装置非线性等效磁路模型。研究了硅钢片表面涡流磁场生成因素与气隙磁场分布,并与有限元仿真结果比较分析。应用该模型在水润滑轴承试验台上进行电磁加载力测试试验。研究结果表明:等效磁路法对磁场分布的表征与有限元法一致,且对气隙的计算更为精确;电磁加载力稳态误差小于4%,响应时间低于0.55 s。

混合励磁式电涡流制退机电磁场与阻力特性分析

电涡流制退机具有无液体泄漏、无需密封、阻力稳定的优势。与目前应用较多的永磁式电涡流制退机相比,混合励磁式电涡流制退机采用线圈替代了一部分永磁体,对阻力特性的调节效果更好。对比了混合励磁式电涡流制退机2种可能的结构形式,然后根据磁路分析与初步计算选择出具有更好阻力性能的结构。针对该结构,利用等效磁路法计算气隙磁场,采用子域模型考虑感生涡流影响,建立了求解混合励磁式电涡流制退机阻力值的等效子域模型。根据某口径火炮反后坐要求,确定了制退机的主要尺寸参数,完成了混合励磁式电涡流制退机结构参数的前期设计,并通过数值计算对解析计算结果进行了验证。接着,针对某口径火炮发射时的工况建立仿真模型,以炮膛合力曲线和复进机力的后坐行程函数曲线作为条件输入,分析强冲击载荷下混合励磁式电涡流制退机的电磁阻尼力、后坐位移和后坐速度规律。最后,分析了不同气隙宽度与内筒的电导率对电磁阻尼力的影响,结果表明气隙宽度越小电磁阻尼力越大,同时过大的内筒电导率会导致电磁阻尼力呈现“马鞍”型。本文研究可为混合励磁式电涡流制退机的工程化应用提供理论基础。

220kV变压器中压侧中性点经小电抗接地的运行分析

北京电网分区运行,其中枢纽站的接地方式关系整个电网运行,K分区中的A变电站采用220 kV变压器中压侧中性点经小电抗接地的运行方式。分析了该分区的主变中性点接地情况、A变电站的等值网络,同时计算了A变电站的短路容量、不同主变并列运行时的单相短路电流,计算表明,中性点经小电抗接地后可降低其单相短路电流,满足设备热稳定性要求。同时提出中性点小电抗投运后对现场运行、倒闸操作的要求。

电磁式线-角振动激振器气隙磁场特性分析

针对传统单轴激振器无法复现线-角空间耦合运动的问题,提出了一种可实现复合振动的电磁式线-角振动激振器磁路结构,并对其气隙磁场特性进行分析。首先构建了激振器的磁路和线圈结构,基于等效电流法,建立了气隙磁场的解析模型,与有限元分析结果的最大相对误差为1.25%,验证了解析模型的正确性;接着研究了各磁路参数对气隙磁场分布特性的影响规律,以及线圈电流产生的磁场与原磁场的耦合效应,并分析了线圈在运动过程中的受力情况;最后研制了激振器磁路拓扑结构样机,分别对线、角振动气隙磁场进行了实验测量,测得结果与有限元计算结果的最大相对误差小于5%,进一步验证了所提出磁路结构的有效性。

考虑动态三相不平衡度的输电线路线损控制方法

为了精准计算线路三相不平衡度并降低线路损耗,治理三相电流不平衡度,研究考虑动态三相不平衡度的输电线路线损控制方法。估算输电线路的三相电压不平衡度,并以其为参考计算输电线路三相电流不平衡度,结合等值电阻法与不平衡度因素计算输电线路的线损,当线路损耗过高时,通过在线路中接入基于电压控制的统一潮流控制器,降低输电线路中的电阻功率值与阻抗,实现输电线路线损控制。实验结果证明,该方法可以有效分析三相不平衡负载下输电线路两端电压、电流波形变化,并准确计算输电线路中三相电流不平衡度,且线损率计算结果准确,控制后线损率呈明显下降趋势。

Equivalent model of multi-type distributed generators under faults with fast-iterative calculation method based on improved PSO algorithm

There are various types of distributed generators (DGs) with different grid integration strategies. The transient characteristics of the fault currents provided by the DGs are different to those of conventional synchronous generators. In this paper, a distribution network with multi-type DGs is investigated, including consideration of DG low-voltage ride through (LVRT). The fault current characteristics of two typical DGs, i.e. an inverter-interfaced distributed generator (IIDG) and a doubly-fed induction generator (DFIG), are analyzed, considering the specific operation modes. Based on analysis of the fault characteristics, an equivalent model of the multi-type DGs under symmetrical/asymmetrical fault conditions is established. A fast-iterative fault calculation method for enhancing the calculation efficiency while avoiding local convergence is then proposed using an improved particle swarm optimization (PSO) algorithm. A simulation system of the distribution network with multi-type DGs is established in PSCAD/EMTDC. The simulation results validate the high accuracy and calculation efficiency of the proposed calculation method of the fault components. This can assist in the settings of the protection threshold.

计及周期/半周期性边界条件的永磁电机子域模型

该文提出的表贴磁极永磁电机考虑周期/半周期性边界条件的子域模型,为舰船大容量直驱多相永磁推进电机的设计优化提供一种快速、高效的工具。介绍周期性边界条件和半周期性边界条件的原理及实现方法,并将其应用到基于等效面电流的子域模型中求解电机气隙磁场,而后通过有限元仿真验证了解析计算的准确性。对比3种求解域下子域模型中谐波系数矩阵的维数和求解速度,表明考虑周期/半周期性边界条件的子域模型在保证结果精度的前提下,能大幅降低矩阵维数,并显著减少求解时间。对实验样机进行空载和负载实验,空载反电势与负载转矩实验结果与解析结果吻合较好,进一步说明了周期/半周期性边界条件下所用子域模型的正确性。

新型永磁无刷直流电机气隙磁密分析

针对微纳卫星飞轮用单圈磁钢无刷直流电机气隙磁密低且干扰磁密大的缺陷,提出了一种新型双圈磁钢构型的无刷直流电机。介绍了飞轮及新型无刷直流电机的结构和工作原理,基于等效面电流法建立新型无刷直流电机的数学模型,推导了气隙磁通密度公式。采用有限元法对有效气隙磁密和干扰磁密进行了磁密分析,结果表明,与传统无刷直流电机相比,新型无刷直流电机有效气隙磁密由0.45T提高到0.55T,气隙平顶宽度由54°拓宽到87°,干扰磁密由0.31T降低到0.065T,有效提升了电机的稳定性能和力矩输出性能,降低了功耗。

短路试验法校验500 kV自耦变压器套管CT电流计算

通过分析大型自耦变压器验收过程中套管CT电流的幅值和相位,介绍了一种利用变压器铭牌参数计算套管CT在短路试验中电流的方法。同时,以某变电站自耦变压器套管CT的验收为例,对所提出的方法进行了分析和验证,可为变电专业工程人员验收自耦变压器套管CT提供借鉴。

大功率电力电子装置等效试验方法及其在电力系统中的应用

大功率电力电子装置核心组件试验的目的是验证其符合设计准则,并确保大功率电力电子装置在正常及故障条件下都能完成预定的工作目标而不至于损坏或影响到所接入的电力系统。随着电力电子装置在电力系统中的广泛应用,大功率电力电子组件的试验技术已成为电力电子技术发展和工程应用极其重要的组成部分。电力电子装置容量的日益提高使得很难直接在电力系统中进行试验,等效试验成为必然的选择。由于其自身的高度复杂性,大功率电力电子组件等效试验方法的研究通常比传统电力设备更复杂、难度更大。大功率电力电子组件试验等效分析的目的是:首先从机理上保证在一定的试验条件约束下,试验方法及试验装置产生的电流、电压、机械和热应力等应与被试电力电子装置在实际运行中所遇到的各种工况具有等价效果;其次是利用必要的试验条件对试品耐受能力作出合理的评价。文章重点对大功率电力电子装置的等效试验机理、等效试验方法和技术应用进行了全面研究,相关研究成果已成功地推动了灵活交流输电技术和高压直流输电技术的工程化进程,为电力系统电力电子技术在中国电网成功应用奠定了重要的理论基础和实验平台。

扩展性微动目标回波模拟与特征参数提取研究

研究了微动目标的多普勒回波模拟及特征参数提取技术.提出了一种基于物理光学法和等效电磁流法的扩展性微动目标回波模拟方法.将在目标坐标系下计算得到的后向散射场通过坐标转换,成为雷达坐标系下的目标回波,通过与解析信号模型对比验证方法的正确性.分析了圆锥与带翼弹头的进动特性,为获得较好的时频聚集性同时避免交叉项采用S-method方法对获取的回波信号进行时频分析,分析了不同雷达波入射角度,不同运动状态及不同几何外形的时频分布特点.对时频分布图进行逆Radon变换,将正弦曲线映射到参数空间,从而获取目标的微动参数.该研究结合电磁散射与信号处理技术,通过对典型弹道目标的仿真,获得一些不同于传统微动模型的结果,结合电磁散射理论,对这些现象进行了解释分析.该研究成果在弹道目标的探测识别领域具有重要的理论与应用价值.

基于等效导热系数的直流电缆稳态载流量简化有限元算法

文中提出一种直流电缆的两层简化结构,以减少应用有限元方法计算直流电缆稳态载流量的计算量,增强其计算效率。将直流电缆结构等效为两层:将除线芯外的各层等效为一层,与线芯构成两层简化结构。等效层的等效导热系数由除线芯外其余各层的导热系数的调和平均数算得。在算例验证中,针对DC 200 k V YJQ41 1×1000+2×12型号直流电缆,分别用有限元方法计算了该电缆原始结构和两层简化结构不同敷设条件下的给定电流时的线芯温度,并与厂商给出的该型号电缆的技术数据参照对比,证明了应用等效导热系数简化电缆结构以进行有限元求解的结果是准确的。之后文中比较了上述计算过程中两种结构下有限元方法的计算量,比较结果表明,两层简化结构的计算量较原始结构的计算量有显著的减少。

架空导线动态增容的热路法稳态模型

应用动态增容技术提高现有架空导线的输送能力,需要准确计算架空导线的隐含容量。为此,首先分析了架空导线动态增容的基本原理并比较了各种传统动态增容模型的优缺点。然后,根据传热学理论建立了架空导线动态增容的热路法稳态模型,该模型仅需监测导线温度以及环境温度,并根据该模型推导了架空导线允许载流量的计算方法。最后,设计了室内、室外架空导线加载不同阶跃电流的温升实验。实验结果表明:在室内较稳定条件下,随着导线温度升高等效热阻RX逐渐减小,当温升达44°C时RX减小了7.7%;室外实验中根据模型计算的允许电流与实际值相对误差为-1.7%。可见,根据架空导线热路法稳态模型可实现对架空导线隐含稳态载流量的准确评估。