A hybrid TLM‐FDTD method for the modelling of diffusion

A new hybrid TLM‐FDTD algorithm for solving diffusion problems is described. The method utilizes the transmission line model to define the time step and the FDTD's leap‐frog algorithm to determine the voltages and currents of the network analogue of the diffusion equation. Unlike the standard TLM method, the proposed one does not generate spurious oscillations. The method is explicit and can be used to solve highly non‐linear problems without the need to solve non‐linear equations. The implementation of a simple adaptive time‐stepping algorithm is also described. Copyright © 2000 John Wiley & Sons, Ltd.     

Transmission parameter representation of non-uniform transmission line Green's functions

The Green's function G(x, x') of a non-uniform transmission line is formulated exactly in terms of partial transmission matrix parameters associated with different segments of the line. Exact differential expressions relate the transmission parameters to each other, and it is shown that G(x, x') can be expressed entirely in terms of a single transmission parameter B(x, x') and its derivatives. The voltage response V(x) on any doubly-terminated line with arbitrary current source density along the line is given. A new perturbation technique, based on a Volterra integral equation, is developed which determines V(x) in terms of known functions and arbitrary perturbing immittances on the line.     

Green's functions for transient plane waves in finite and infinite lossy media

Contents This paper treats the Green's functions of transient plane waves in lossy media for finite and infinite regions. For infinite regions they are given by two essentially different infinite series, one converging extremely rapidly for small times, one for large times. In the limit of infinite light velocity one obtains diffusing fields in terms of -functions, discussed in a preceding paper [1]. They can also be represented by two essentially different infinite series related to one another by Jacobi-transformations. So the present paper generalises the results of the earlier one.

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Transiente ebene Wellen in unendlichen und endlichen verlustbehafteten Medien

Übersicht In der vorliegenden Arbeit werden die Green'schen Funktionen transienter ebener Wellen in endlichen und unendlichen verlustbehafteten Medien behandelt. Im Fall endlicher Medien können diese durch zwei wesentlich verschiedene unendliche Reihen dargestellt werden, deren eine für kleine, Zeiten, deren andere für große Zeiten extrem rasch konvergiert. In der Grenze unendlicher Lichtgeschwindigkeit ergeben sich diffundierende elektromagnetische Felder, die in einer vorhergehenden Arbeit behandelt wurden [1]. In diesem Spezialfall sind die Felder durch -Funktionen gegeben, deren unterschiedliche Reihendarstellungen über die Jacobi-Transformationen miteinander zusammenhängen. Die Ergebnisse der vorliegenden Arbeit verallgemeinern diese Zusammenhänge.

     

Discrete modelling of transport processes in two spatial dimensions

A random flight model of linear transport processes in two spatial dimensions is considered and solved exactly in closed algebraic form. Its one-dimensional version had been proposed by Taitel as a means to overcome the paradox of infinite speed of propagation within classical heat diffusion theory. The connection with hyperbolic diffusion theory is complemented here by deriving the discrete fluxes and their relaxation term. Moreover, such an approach circumvents the discretization of a continuum model for an intrinsically discrete process, when diffusion processes are to be solved numerically. Finite samples are treated by means of the reflection method. Some applications of these general results are mentioned.     

TLM modelling of the diffusion approximation of queuing system

This paper provides an application of the TLM method to any queuing systems that can be approximated as a diffusion process. The TLM node has been extended in order to take into account the variables associated with the diffusion approximation of the queue, which is presented in Harrison, Patel, Performance Modelling of Communication Networks and Computer Architectures, Addison‐Wesley: Reading, MA, 1994. The analytical solution is compared with the TLM numerical results. Copyright © 2001 John Wiley & Sons, Ltd.     

Implementation of timestep changes in transmission-line matrix diffusion modelling

This paper details general expressions for implementing timestep transformations in transmission-line matrix (TLM) modelling of diffusion processes. The expressions can be conveniently incorporated into any TLM routine which models multidimensional problems using a variable meshing technique.     

Higher-order modelling of the diffusion dynamics in a bipolar transistor

A higher-order diffusion model for a bipolar transistor has been developed. This model is based on the Padé approximation of the quasi-static expansions of the base and collector currents and gives improved accuracy for the simulation of fast transients and periodic operation at high frequencies. the effect of higher-order circuit elements on accuracy is demonstrated by calculating the transient response to a step excitation and by determining the scattering parameters of a transistor model with higher-order elements linearized about an operating point. the higher-order model is replaced by an equivalent circuit including only conventional elements, and the transient behaviour of these two models is compared.     

Numerical modelling for simulation and treatment planning of prostate thermal therapy

A 2D transmission line matrix model is used to study thermal transfer in living tissues exposed to laser energy. Damage size because of thermal coagulation in thermal treatment of benign prostate hyperplasia is determined quantitatively. Results show a quasilinear dependency of blood perfusion on temperature at the beginning of coagulation. Immediately thereafter, blood perfusion decreases considerably until it shuts down when the tissue under investigation has been coagulated. Increase in perfusion rate (ω) leads to high values of t₁₀₀, which is the time required to reach a primary zone temperature of about 100 °C, and reflects the increased cooling created by perfusion. The transmission line matrix numerical model predicts the coagulation damage contours; that way, it has a clinical interest in therapy as an aid for clinicians because damage cannot be easily measured within patients. Results are validated through comparison with other researches. Copyright © 2014 John Wiley & Sons, Ltd.     

TLM modelling of diffusion,drift and recombination of charge carriers in semiconductors

The paper provides an extension to the one-dimensional TLM diffusion model. The extended diffusion node presented here models the exact transport equation with diffusion drift and recombination of charge carriers in semiconductors. A general algorithm for providing a numerical solution to the transport phenomena is also presented here. The analytical solution for infinitely long semiconductors is compared with the TLM numerical results.     

太阳电池光伏光热一体化系统的性能研究

为了提高太阳能的综合利用效率,同时获取电能和热能,将铜管换热器加装在太阳电池板背,构成太阳电池光伏光热(PV/T)一体化系统。采取对比实验法在呼和浩特地区对太阳电池板进行光伏光热性能测试。实验结果表明,在相同的太阳辐照度和环境温度条件下,装有铜管换热器的单块太阳电池的输出功率比普通单块太阳电池实际输出功率提高近17%。     

Non‐unique solutions in drift diffusion modelling of phototransistors

We report non‐unique solutions for the potential in a Drift Diffusion (DD) model of a two terminal phototransistor. These solutions are present under bias without illumination, and persist until high illumination levels. It is well known that the DD equations can yield non‐unique solutions for pn structures which contain three or more junctions and two terminals with applied biases greater than k_BT log 2 where k_BT is the thermal energy at a temperature T, but DD models of phototransistors under illumination have been less well studied. The implicit belief is that one needs to artificially impose a potential in the base of the phototransistor in order to obtain a unique solution. We show here that this is only necessary because of a weakness in the numerical methods used to solve the equations, and describe two methods which circumvent this for which we show that this problem does not occur. These methods are used to investigate the operation of GaAs and In_0·53Ga_0·47As homojunction phototransistors, including the influence of the position of the illumination region and base doping. Copyright © 2000 John Wiley & Sons, Ltd.     

混合式配电变压器数字控制系统离散域建模与稳定性分析

为准确分析混合式配电变压器(HDT)数字控制系统的特性,构建了HDT连续-离散混合控制模型,并分析了HDT数字控制系统的稳定性。针对所建立的HDT数字控制系统离散域模型,考虑采样和零阶保持器引入的延时环节的作用,结合双线性变换并利用朱利判据推导了离散域下HDT控制系统比例积分参数的约束条件,进而分析并揭示了采样周期对于HDT数字控制系统稳定性的影响规律,并确定合理的数字控制参数。最后通过仿真以及实验验证了理论分析的正确性。     

Maximum loadability of power systems using hybrid particle swarm optimization

The problem of voltage stability is one of the main concerns in the operation of power systems. There are different approaches to estimate the voltage stability of the system. One of these approaches is to find the margin from the current operating point to the maximum loading point of the system. Finding this maximum loading point can be formulated as an optimization problem. This paper utilizes the newly developed evolutionary particle swarm optimization in solving this optimization problem. Details of the implementation of the proposed method to two test systems (Ward-Hale 6-bus) and (IEEE 14-bus) are presented. The results are compared to those obtained by the widely used continuation power flow technique. Good agreement has been obtained proving the validity and applicability of the proposed method.     

基于蝙蝠与粒子群混合优化算法的光伏MPPT研究

在局部遮荫条件下,传统最大功率点追踪(MPPT)算法容易失效,群智能优化算法追踪时间较长.为此,提出了一种基于蝙蝠与粒子群混合优化(BPSHO)的MPPT算法.在算法的前期,采用蝙蝠算法;在算法中后期,采用粒子群优化算法.按照指数规律调节算法的参数,并在算法的中期加入局部搜索机制.仿真与实验结果表明:BPSHO算法能够...     

基于混合粒子群算法的源-荷-储协调优化调度

为了提高新型电力系统中对风电和光伏的消纳能力,降低电力系统运行成本,将火电机组、光伏、风电、需求响应负荷和储能系统作为调度资源建立了基于源-荷-储协调的优化调度模型。以火电机组运行成本、弃风弃光成本和需求响应负荷调度成本最小为目标,提出了一种两阶段优化方法。第一阶段优化采用离散二进制粒子群优化算法,使火电机组启动成本和弃风弃光成本之和最小。在第一阶段优化结果的基础上,第二阶段的优化采用双层连续粒子群优化算法使基于电价的需求响应负荷调度成本和燃料成本之和最小。算例结果验证了该优化调度模型的可行性和有效性。     

A comparative study of two TLM networks for the modelling of diffusion processes

A comparative study of two alternative networks for TLM modelling of diffusion processes has been undertaken. Some of their inherent advantages and disadvantages are analysed according to the ratio between the impedance of the lossless transmission lines and the lumped resistance. Their relative accuracy and utility in controlling the timestep automatically are examined.     

Use of lossless transmission‐line segments and shunt resistors for TLM diffusion modelling

In diffusion modelling by means of the transmission‐line matrix (TLM) method, a nodal arrangement of using lossless transmission‐line segments and series resistors is almost exclusively adopted and is currently considered as a standard approach. In this paper, the use of shunt resistors instead of series resistors is shown to represent an equally valid configuration. As a starting point, we have derived the telegrapher's equation in its most general form for TLM modelling of diffusion processes. A general algorithm based on the shunt‐resistor TLM model for implementing a numerical solution of the diffusion equation in multiple dimensions is given. Fundamental analysis and calculated examples confirm that the alternative shunt‐resistor configuration does not exhibit the unwanted absorption effects suggested by a recent paper (Internat. J. Numerical Model.: Electronic Networks, Devices and Fields 2002; 15 :261). Copyright © 2003 John Wiley & Sons, Ltd.     

热退火中应变量子阱的扩散激活能的研究

进行了可用于太阳电池的应变量子阱的退火性质研究,并对传统数据分析方法进行了改进,提出一种新的应变量子阱热退火扩散激活能的拟合方法,理论与实验结果吻合较好.     

基于遗传粒子群混合算法的机组组合优化

节能发电调度的目标是实现能耗量最小,合理安排机组发电计划则更为至关重要。在参考文献的基础上,提出了一种用于机组组合优化的遗传粒子群混合优化算法。先用遗传算法求解机组组合,再用粒子群优化算法求解负荷经济分配。按照节能调度思路对遗传算法进行了改进,提高了优化性能。给出了10机算例系统优化结果,验证了该混合算法的可行性和有效性。     

基于遗传粒子群混合算法的机组组合优化

节能发电调度的目标是实现能耗量最小,合理安排机组发电计划则更为至关重要.在参考文献的基础上,提出了一种用于机组组合优化的遗传粒子群混合优化算法.先用遗传算法求解机组组合,再用粒子群优化算法求解负荷经济分配.按照节能调度思路对遗传算法进行了改进,提高了优化性能.给出了10机算例系统优化结果,验证了该混合算法的可行性和有效性.