TIME DOMAIN ELECTROMAGNETIC FIELD COMPUTATION WITH FINITE DIFFERENCE METHODS

The solution of Maxwell's equations in the time domain has now been in use for almost three decades and has had great success in many different applications. The main attraction of the time domain approach, originating in a paper by Yee (1966), is its simplicity. Compared with conventional frequency domain methods it takes only marginal effort to write a computer code for solving a simple scattering problem. However, when applying the time domain approach in a general way to arbitrarily complex problems, many seemingly simple additional problems add up. We describe a theoretical framework for solving Maxwell's equations in integral form, resulting in a set of matrix equations, each of which is the discrete analogue to one of the original Maxwell equations. This approach is called Finite Integration Theory and was first developed for frequency domain problems starting about two decades ago. The key point in this formulation is that it can be applied to static, harmonic and time dependent fields, mainly because it is nothing but a computer-compatible reformulation of Maxwell's equations in integral form. When specialised to time domain fields, the method actualy contains Yee's algorithm as a subset. Further additions include lossy materials and fields of moving charges, even including fully relativistic analysis. For amny practical problems the pure time domain algorithm is not sufficient. For instance a waveguide transition analysis requires knowledge of the incoming and outgoing mode patterns for proper excitation in the time domain. This is a typical example where both frequency and time domian analysis are essential and only the combinatin yields the successful result. Typical engineers may wonder why at all one should apply time domain analysis to basically monochromatic field problems. The answer is simple: it is much faster, needs less computer memory, is more general nad typically more accurate. Speed-up factors of over 200 have been reached for realistic problems in filter and waveguide design. The small core space requirement makes time domain methods applicable on desktop computers using milions of cells, and six unknowns per cell—a dimension that has not yet been reached by frequency domain approaches. This enormous amount of mesh cells is absolutely neceesary when complex structures or structures with spacial dimensions of many wavelengths are to be studied. Our personal recod so far is a waveguide problem in which we used 72,000,000 unknowns.     

A MODIFIED FINITE DIFFERENCE METHOD FOR MODELLING DIFFUSION PROCESSES

A time domain unconditionally stable explicit method is presented which may be used to model processes governed by the diffusion equation such as transient heat flow. Unlike the explicit finite difference routine, the method models the diffusion process within the time step (MPWT). Being explicit, the method (MPWT) may easily account for non-linear physical parmeters and may be compared with the transmission line matrix (TLM) method of diffusion modelling in terms of its utility. Unlike the TLM model, however, the equivalent circuit does not contain inductive components which have no clear physical meaning. The MPWT method is based on a simple resistive and capacitive circuit model, which for short time steps reduces to the explicit finite difference formulation but is stable for large time steps. Good agreement has been found when results obtained using this algorithm are compared with other numerical methods and analytical results.     

基于EE模型的励磁系统参数时域辨识法

提出一种基于EE（方程误差）模型的时域辨识算法，通过对离散采样数据的多重积分（PLPF法）估计模型参数值，直接求取待辨识系统微分方程的系数；再根据微分方程的系数，由特定系数法得到一个非线性方程组，然后用牛顿迭代法求解得出传递函数的模块环节实际参数。该方法的优点在于根据输入输出采样数据直接在时域上进行参数辨识，方法简便，较好地解决了由传递函数多项式a,b系数转化为传递函数框图环节参数的实际需求。该方法通过工业试验得到校核验证。     

TIME DOMAIN MODELLING FOR ELECTRICAL MACHINES

ABSTRACT

In electrical machine problems the mechanical time constant is usually assumed greater than the electrical time constants. Based upon this assumption and using a numerical formula for the evaluation of the Laplace transform inversion integral, a time domain method is developed for the solution of transient problems of machines. This method provides simple problem formulation, fast solution speed and high accuracy. It is applicable to system problems.     

电压源型超导磁储能装置特性的全时域仿真研究

介绍了电压源型超导磁储能装置（VSMES）的基本结构和工作原理，在Matlab环境下建立了VSMES的全时域仿真模型，利用所建立的模型对VSMES的稳态和动态特性进行了详细的时域仿真研究。详细分析了一个稳态周期内，各阶段VSMES的物理工作过程和能量流传情况，并在此基础上总结了VSMES系统参数对其特性的影响特点。动态研究着重分析了系统参数对其动态响应的影响，以及在电力系统暂态过程中的作用。所得结论为VSMES系统的设计、运行和参数选择提供了依据。     

TIME DOMAIN ESTIMATION TECHNIQUES FOR HARMONIC LOAD MODELS

ABSTRACT

In this paper we present two novel time domain techniques for load modelling in the presence of harmonics. In the first technique, the harmonic contents of the load voltage and current waveforms are assumed to be known in advance. The second technique uses samples of the load voltage and current waveforms directly. The least errors square parameter estimation algorithm is used to estimate the load resistance, inductance and capacitance. The residual current associated with incomplete extraction of the parameters for all significant signal frequencies is also estimated. We also identify harmonics that are not common between the load voltage and current waveforms. The proposed techniques are applied to synthetic and actual recorded data. The paper's conclusions are based on comparing the results obtained using both techniques.     

一种临界故障切除时间概率分布的求解方法

稳定性分析是电力系统运行与控制中必须考虑的一个以及半不变量的性质，在敏感度计算的基础上，将临界故障最基本的问题。传统稳定分析是在确定系统初始参数后进行的。由于某些原因，电力系统的初始参数，如母线负荷等，因得不到其确定值而只能知道其可能分布。这使得传统的稳定分析方法已不能适用于新的形势，为此提出了概率稳定分析这一新的课题。该文提出一种新的临界故障切除时间概率分布的求取方法，利用随机变量的Cram-Charlier级数展开式切除时间概率分布的求取转化为对初始参数的半不变量的求取。该算法在39机系统中进行了测试，与Monte-Carlo仿真结果相比，该算法不需要反复进行大量的数值仿真的采样计算，而只需在确定临界故障切除时间的灵敏度时进行一次数值仿真；计算结果能很好地描述临界故障切除时间的实际概率分布，且能显著地减少计算量，提高计算速度。利用该方法，可根据故障后临界故障切除时间的概率分布，确定临界故障切除时间分布在期望值附近某区间内的概率，为稳定分析提供了判断的依据。     

交流发电机整流系统传导电磁干扰的时域模型与仿真分析

该文针对交流发电机整流系统的传导电磁干扰进行时域仿真研究。对一实际系统进行了实验测试，基于传导EMI产生机理的分析，建立了可对系统传导EMI进行仿真研究的时域模型，并且考虑了系统中高频段不可忽视的寄生参数的影响。通过把每组绕组分成数阶相同的π型电路来描述电机绕组的分布寄生参数，给出了提取电机高频模型中分布参数的一种方法。把系统简化为由主要寄生参数组成的谐振电路，利用MATLAB软件对实验系统的传导电磁干扰进行时域仿真研究，通过实验和仿真结果的对比验证了模型的正确性。     

求解压力耦合方程的全隐算法--CIMPLE算法

提出了一种计算流场的全隐算法ＣＩＭＰＬＥ算法,并通过两个具体算例与ＳＩＭＰＬＥＲ算法进行了比较,计算结果表明,该算法有更好的收敛性。     

抽水蓄能电站前导时间短的动态效益定量评估方法

提供了一种新的抽水蓄能电站前导时间短的动态效益定量评估方法，即在考虑了系统中机组动态特性的基础上，优化电力系统电源分布，改进发电模型和响应容量模型，以风险度为指标分析系统承受的能力，从而为抽水蓄能电站的建设提供一定的依据。     

解一阶双曲型方程的高精度差分格式

本文构造出解一阶双曲型微分方程初值问题的一种高精度隐式差分格式,作误差分析得其精度为 o(t~4)+o(△x~4)并给出该差分格式稳定的条件为|r|<1/     

瞬时性故障最佳重合时刻的一种捕捉方法

在重合闸之前,按故障线路切除时的系统稳定平衡点和导纳矩阵来计算系统的暂态能量时,这一能量是守恒 的。文中通过分析计算指出,对于瞬时性故障,如果以重合闸成功后的稳定平衡点和导纳矩阵来计算重合闸 前系统的暂态能量,这一能量的大小 是变化的,这一变化的能量达到最小值的时刻就是瞬时性故障重合闸的 最佳时刻。     

一种区域自组织的分级网络层移动性管理方法

移动性管理是移动通信系统中的关键技术之一。给出了面向下一代移动通信系统的基于IP扩展技术的网络层移动性管理的体系结构、功能模型。提出了一种基于区域自组织的分级网络层移动性管理方案，即DDA-HNMM(Domain Discovery Assisted Hierarchical Network-Layer Mobility Management)方案。针对网络业务强度的不均匀性，给出了一种切换强度发现算法和区域自组织机制。仿真结果表明，灵活的区域自组织可以明显减少信令开销，提高移动终端的吞吐量。     

乒乓式转子一点接地保护的原理改进方案

论述了乒乓式转子一点接地保护的原理改进方案。通过叠加辅助的直流电源,消除了该保护在发电机停机或无励磁空转状态不能检测发电机转子绕组接地故障的缺憾     

电网调度实时计算机系统综合评估的模糊数学方法

对电网调度实时计算机系统的性能指标进行全面分析后，从规划、设计及实用 化达标的角度，首次根据模糊集合原理将其合理划分为六大因素集及若干子集 ，统计得出了相应的实用权重向量。在此基础上，提出了对地区电网调度实时 计算机系统进行综合评价的模糊评估方法。该方法具有简明、说服力强、易于 实施的特点。     

电力系统自动化GPS精确对时的解决方案

针对电力系统及自动化统一对时,提出了一个变电站内共享一台 Ｇ Ｐ Ｓ,利用 Ｇ Ｐ Ｓ 同步产生 Ｉ Ｒ Ｉ Ｇ＿ Ｂ 码,通过 Ｒ Ｓ＿４２２／４８５ 对所有微机保护及自动化装置统一对时,该方案具有 Ｇ Ｐ Ｓ资源共享,对时准确等特点。     

解决电厂MIS实时子系统通信和存储问题的实施方案

实时子系统是发电厂管理信息系统(MIS)的重要组成部分，它要求安全、足够快速地实现生产现场数据的单向传输和定期存储。针对不同的机组，采用了相应的通信方式：动态数据转换(DDE)通信、UDP通信和串口通信，进行数据传榆，并对这些数据选用了合适的存储方式。实践征明，这种方法成功地解决了数据通信和存储的问题，进而提高了电厂生产管理和决策的效率。     

错时采样空间矢量调制技术的频域数学分析

错时采样空间矢量调制是一种新型的开关调制策略,能够在较低的器件开关频率下实现较高等效开关频率的效果,具有良好的谐波特性。文中以不连续脉宽调制为例,首先将其调制波显化,并通过双重傅里叶变换得到其频域数学模型。在此基础上,推导了错时采样空间矢量调制技术的频域数学模型,从而在理论上证明该技术能够大大提高装置的等效开关频率,同时没有基波损失。这个结论普遍适用于各种载波脉宽调制技术。仿真和实验验证了理论分析结果。     

时间序列小波神经网络在故障测距中的应用

在小电流接地系统单相接地故障特征分析的基础上,提出了一种基于故障后暂态电气量由时间序列小波神经网络原理来实现的直配线路单相接地故障测距方法。给出了广义的小波神经网络概念,提出了适合暂态时间序列分析的小波神经网络模型并应用于小电流接地系统直配线故障测距。理论及大量的EMTP仿真结果表明此方法是可行的,且具有较好的故障测距性能。     

基于有限元方法的电缆变压器绕组的热路模型研究

对一个电缆变压器的绕组,通过求解有限元方程,得到其温度场和热气流场的分布。在此基础上,建立其分布参数的热路模型。利用该模型经修正后求解了不同负载条件下绕组的温度分布,并将有限元法计算值和实测值进行了比较,证明了模型的正确性。这种方法为研究该类变压器的温度特性提供了方便。