A modular parallelization framework for power flow transfer analysis of large-scale power systems

Power flow transfer(PFT) analysis under various anticipated faults in advance is important for securing power system operations. In China, PSD-BPA software is the most widely used tool for power system analysis, but its input/output interface is easily adapted for PFT analysis,which is also difficult due to its computationally intensity.To solve this issue, and achieve a fast and accurate PFT analysis, a modular parallelization framework is developed in this paper. Two major contributions are included. One is several integrated PFT analysis modules, including parameter initialization, fault setting, network integrity detection, reasonableness identification and result analysis.The other is a parallelization technique for enhancing computation efficiency using a Fork/Join framework. The proposed framework has been tested and validated by the IEEE 39 bus reference power system. Furthermore, it has been applied to a practical power network with 11052 buses and 12487 branches in the Yunnan Power Grid ofChina, providing decision support for large-scale power system analysis.

Modelling Study to Compare the Flow and Heat Transfer Characteristics of Low-Power Hydrogen,Nitrogen and Argon Arc-Heated Thrusters

A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters （arcjets） for three different propellants： hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, velocity and Mach number distributions calculated within the thruster nozzle obtained with different propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the flow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip; the flow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant flows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, specific enthMpies and thermal conductivities, are different, there are appreciable differences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest specific impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.

Computational analysis of the flow of pseudoplastic power-law fluids in a microchannel plate

The flow of pseudoplastic power-law fluids with different flow indexes at a microchannel plate was studied using computational fluid dynamic simulation.The velocity distribution along the microchannel plate and especially in the microchannel slits,flow pattern along the outlet arc and the pressure drop through the whole of microchannel plate were investigated at different power-law flow indexes.The results showed that the velocity profile in the microchannel slits for low flow index fluids was similar to the plug flow and had uniform pattern.Also the power-law fluids with lower flow indexes had lower stagnation zones near the outlet of the microchannel plate.The pressure drop through the microchannel plate showed huge differences between the fluids.The most interesting result was that the pressure drops for power-law fluids were very smaller than that of Newtonian fluids.In addition,the heat transfer of the fluids through the microchannel with different channel numbers in a wide range of Reynolds number was investigated.For power-law fluid with flow index(n=0.4),the Nusselt number increases continuously as the number of channels increases.The results highlight the potential use of using pseudoplastic fluids in the microheat exchangers which can lower the pressure drop and increase the heat transfer efficiency.

Non-Axisymmetric Mass Transfer Phenomenon behind an Orifice in a Curved Swirling Flow

The purpose of this paper is to understand the mechanism of non-axisymmetric wall-thinning that caused a pipe break in the pipeline of the Mihama nuclear power plant in 2004. The wall thinning was caused by the flow accelerated corrosion which affects low carbon steel pipelines. The mass transfer rate measurement of the wall thinning behind an office in a curved swirling flow is carried out in a closed-circuit water tunnel using a benzoic acid dissolution method. The experimental results indicate that the high mass transfer rate is observed on one side of the pipe behind the orifice, which is similar to the observation of the wall-thinning rate in the Mihama case. This result suggests that the influence of the secondary flow in the long elbow combined with the swirling flow can produce the non-axisymmetric mass transfer phenomenon behind the orifice.

Optimal Design for Wireless Power Transfer System with Relay Resonators

The optimization method by adjusting load and distances between two adjacent coils( or resonators) is presented on basis of wireless power transfer( WPT) system with relay resonators. 2-port network and impedance matching theory are applied to analyzing power flow of incidence and reflection in WPT system,then setting up power flow model. The maximum power transmission efficiency can be obtained when the load and distance between secondary resonator and output coil meets impedance matching at 2-port network's output port. The simulation and experimental results shown the impedance matching method can effectively improve and maintain transmission efficiency by adjusting load and distances between coils or relay resonators.

云边协同下的电网脆弱线路辨识方法设计

针对以单纯云计算为基础的电网脆弱线路辨识中,存在主节点计算压力大、耗时过高的问题,引入云边协同方法,设计了一种以云边协同为基础的电网脆弱线路辨识方法。以云边协同逻辑架构为基础,将云计算与边缘计算相融合,构建电网脆弱线路辨识模型。利用PageRank算法建立DNS缓存,整合云计算下的边缘设备数据源,以基尔霍夫定律为基础,计算不同线路的潮流值,根据潮流结果完成电网脆弱线路辨识。结果表明,所提方法对电网中的脆弱线路辨识性能更强、耗时更短。

Mass transfer coefficients in metallurgical reactors

An overview on the application and achievements of physico-mathematicalmodeling of metallurgical processes in China is briefly declared. The important role of coefficientsin model formulation is shown from our experience. The mass transfer coefficients of the slag-metalreactions and the gas-metal reactions are discussed referring to the flow conditions near theinterface. The influence of the surface-active species on the mass transfer and the interfacialreaction is also discussed briefly.

基于TPA的船舶机械系统振动传递特性分析

为有效降低船舶机械系统低频线谱振动,采用传递路径分析方法(transfer path analysis,简称TPA)对典型船舶机械设备振动沿管路系统与浮筏基座传递规律进行试验研究。试验结果表明,通过传递路径分析方法辨识各路径振动贡献量合成结果与直接测量结果一致,证明了本研究方法与测试数据的正确性。通过传递路径与输入船体结构振动功率流贡献量分析,发现设备低频段振动能量主要通过浮筏基座进行传递,整个试验模型的低频线谱成分由管路系统与船体耦合引起。该研究结果可为船舶机械系统低频线谱主动控制作动器的位置优化与频率选取提供参考。

基于优化模型的有源配电网可靠性评估方法

现有的有源配电网可靠性评估方法中,模拟法难以得到确切的指标计算结果,解析法难以处理动态孤岛最优切负荷问题。该文提出一种基于优化模型的有源配电网可靠性评估方法。该方法考虑分布式电源随机性、故障转供以及潮流倒送限制等因素,首先建立分布式电源的多状态模型,并基于后向场景缩减算法对分布式电源出力的随机场景进行状态缩减。针对缩减的特定场景,提出面向可靠性指标评估的混合整数线性规划模型,通过求解该模型,利用寻优的机制得到系统的各类可靠性指标。该方法的主要优点在于便于考虑配电网可靠性与网络规划优化问题的相结合。通过算例分析了该方法的准确性,并通过有源配电网自动、手动开关配置优化问题说明所提方法的延伸应用价值。

基于强化传质的质子交换膜燃料电池流道优化

针对质子交换膜燃料电池(PEMFC)的性能与其传质性能密切相关以及流道优化设计对PEMFC的传质性能影响显著的特点,设计了一种截流流道,并在阴极流道内部设置了新型的三维凸台,使其对空气产生截流效应.对比了直流道与不同配置的截流流道对PEMFC传质性能的影响,分析了不同截流单元流道的电池水气分布、净功率及有效传质系数的变化规律.研究结果表明:截流流道能有效提升电池性能,优化水气分布,提高最大净功率和有效传质系数;与直流道相比,下游局部凸台分布加密的截流流道的电流密度最大提升约29.2%,最大净功率提高10.5%~11.7%,有效传质系数增加50.2%~100.7%.

电解水制氢的多物理场建模与监控技术综述

电解水制氢设备中存在电流、温度、流速等多个物理量以能量和物质双重耦合的形式分布于电解槽内,其高效运行离不开对内部多物理场的精确解析与协调控制。对电解水制氢设备中多物理场建模与调控技术进行了系统性综述,系统揭示了电解水制氢设备内传热、传质、气液两相流等多物理过程的耦合机理,并依次综述了各物理场的现有建模技术、研究瓶颈及发展趋势;同时,给电解槽施加磁场和光场可有效监测或调控其内部的多物理过程,分别介绍了外加光场的流场监测原理以及外加磁场的调控技术。最后,总结了电解水制氢设备内场建模与外场调控研究的关键技术与发展方向,以期为电解水制氢设备的多物理场研究的发展提供指导。

阀控充液式液力偶合器换热特性研究

在液力偶合器的使用过程中,由于转差损失与液力损失,会使其工作水液的温度上升,进而影响液力偶合器的工作性能,为了解决这一问题,对阀控充液式液力偶合器的换热特性进行了研究。首先,构建了含有进出水口双腔流道的瞬态换热计算模型,并对其进行了网格无关性验证;然后,采用多步求解方式对正常运转工况、堵转工况及循环换水工况的流动换热进行了数值模拟计算;最后,对比分析了不同工况下的液力偶合器温度场分布特性,探讨了液力偶合器内流场的流动换热变化规律。研究结果表明:正常工况及堵转工况流场整体温度皆呈现明显的线性上升趋势;以240 L/min流量进行循环换水时,流场温度呈先快后慢的下降趋势,20 s内可将流场温度降至30℃左右。采用该研究结果,可以准确地预测液力偶合器内流场温度变化,可为液力偶合器优化、换水调控提供理论参考。

三明治耦合板的能量辐射传递模型

该研究的目的是将能量辐射传递法(radiative energy transfer method,RETM)推广到三明治耦合板模型中。推导了三明治板的振动控制方程,获得结构的波传播特性参数。基于波法推导了三明治耦合板的能量传递系数。根据能量密度控制方程,得到能量密度和功率流强度的核函数。根据惠更斯原理,结构内部的能量可由实源辐射的直接场能量与边界虚源的反射场能量叠加得到。求解第二类Fredholm积分方程获得边界虚源的强度。数值算例结果与模态叠加和功率流分析(power flow analysis,PFA)对比,验证了所建模型的正确性和准确性。对L型耦合三明治板求解,获得其能量密度和功率流分布特征。

挡板分布对PEMFC传质特性的影响

合理的双极板流道结构设计对提高质子交换膜燃料电池(PEMFC)性能具有重要意义。建立单直流道PEMFC的三维模型,并在流道出口处添加矩形挡板,研究挡板间距及堵塞率对PEMFC传质特性和输出性能的影响。在流道出口处添加挡板,可强化流道内反应气体传质效果;增大挡板间距或提高挡板堵塞率,均能提高扩散层中的氧气浓度,改善PEMFC输出性能。提出一种挡板数量为5、间距为0.90 mm、间距差值为0.40 mm、堵塞率为75.00%及堵塞率差值为2.50%的挡板分布设计方案。与无挡板流道相比,该方案的峰值功率密度提高了4.96%。

电动汽车动力电池液流换热板换热特性的数值分析

电动汽车动力电池在温度过高或过低时,均需要通过换热板进行热交换,以确保动力电池的工作性能。基于此,设计了3种不同流道结构的液流换热板,采用计算流体力学方法分析了流道横截面积和流道长度对动力电池散热和加热效果的影响。结果表明:增加内流道横截面面积可以增强换热板与流体之间的传热效果;在横截面面积不变的情况下,增加流道长度可使换热板表面温度分布更均匀。

基于潮流熵的电网连锁故障传播元件的脆弱性评估

为研究电网连锁故障机理,同时判别出连锁故障传播过程中的关键脆弱元件,从熵的基本原理出发,结合过负荷与断线扰动下潮流的分布特性,提出了基于潮流熵的脆弱元件评估模型。通过对新英格兰10机39节点系统的模拟计算,节点单位过负荷扰动下,节点的潮流分布熵越小,越容易导致系统支路越限,节点越脆弱;支路受"发电机—负荷"节点对的潮流冲击越大、支路潮流转移熵越小,支路越脆弱,在连锁故障中起到关键传播作用;与基于介数、风险等方法的脆弱元件判别结果相比,基于潮流熵的脆弱元件评估模型物理意义明确,计算速度快,脆弱元件集符合实际情况。

基于潮流熵测度的连锁故障脆弱线路评估及其在四川主干电网中的应用

运用熵的基本原理,结合电网扰动下线路潮流转移和分布特性,提出线路潮流转移熵和线路潮流分布熵的概念。针对不同运行状态下电网脆弱环节的转移特点和过负荷与故障断线扰动下线路潮流熵的变化特点,考虑电网实时运行风险,提出基于潮流熵的脆弱评估模型。IEEE 30节点系统仿真结果验证了所提方法的可靠性和全面性。丰大和枯大方式下四川主干网应用表明,潮流分布熵越大、潮流转移熵越小的线路过负荷冲击脆弱度越大;潮流负载较重、运行故障率高、潮流转移熵较小的线路故障断线风险脆弱度高;丰大、枯大期电网的脆弱环节发生转移;基于潮流熵的电网综合脆弱线路与电网实际薄弱环节相吻合。

基于马尔可夫链的电力系统连锁故障预测

近年来,国内外发生了多起连锁故障引起的大面积停电事故,因此对连锁故障的预测就成了电力系统领域内受到普遍关注的重要问题。现有的连锁故障预测方法未能把网络拓扑结构、前后级故障间的关联、系统不确定性等因素系统而综合地利用起来。在此背景下,提出基于马尔可夫链的连锁故障预测方法,其能够计及系统前后级故障视在功率转移关系、保护/断路器不正确动作的可能性、系统硬件失效率等因素。首先,根据系统初始故障概率和各级故障之间的状态转移概率,预测系统连锁故障的发展趋势,预测出下一级可能的故障集,得到具有时间先后顺序的连锁事故路径。之后,提出了3个脆弱性指标来评估后续故障对系统的影响,以便对可能的连锁故障加以监视和快速控制。最后,用IEEE 10机39节点系统说明了所发展的模型和方法的基本特征。

稳定控制所用交流设备跳闸判据的分析及应用

电力系统安全稳定控制装置的动作行为直接影响电网的安全运行。对设备跳闸、尤其是交流输电线路跳闸的正确判断是稳定控制装置正确动作的重要前提。论述了用电气量判断输电线路跳闸的必要性,研究、分析了线路跳闸电气量的变化特征,以及潮流转移、失步振荡、低频振荡等动态过程中电气量变化与线路跳闸的区别;对目前使用的跳闸判据及有关判别条件的正确含义进行了解释,分析了现场运行中所出现的误判事件的原因,指出目前使用的跳闸判据的正确性;提出了防止误判跳闸的有效措施。文中讨论的内容将有助于澄清目前国内在这方面存在的分歧和认识方面的误解,以提高安全稳定控制系统运行的可靠性。