An Extended DC Power Flow Model Considering Voltage Magnitude

A quasi-linear relationship between voltage angles and voltage magnitudes in power flow calculation is presented.An accurate estimation of voltage magnitudes can be provided by the quasi-linear relationship when voltage angles are derived by classical DC power flow.Based on the quasi-linear relationship,a novel extended DC power flow(EDCPF)model is proposed considering voltage magnitudes.It is simple,reliable and accurate for both distribution network and transmission network in normal system operation states.The accuracy of EDCPF model is verified through a series of standard test systems.

Asymptotically Optimal Scenario Analysis and Wait-and-See Model for Optimal Power Flow With Wind Power

精确模拟风功率分布的场景,有效求解反映风电随机性的最优潮流模型,对大规模风电并网的经济调度、质量控制及安全运行均具有重要意义。引入风电随机变量,建立最优潮流的＂wait-and-see＂（WS-OPF）模型;采用优于其他指标的瓦瑟斯坦（Wasserstein）距离为衡量指标,形成与风功率概率分布最优近似的场景模型,生成渐近最优场景,获得潮流分布及机组最优出力等指导调度安全经济运行的重要信息。最后,以IEEE 30和IEEE 300系统为例,对比各种距离指标的模拟精度,验证Wasserstein距离的优良性;同时,与不考虑风电随机性的模型相比,WS-OPF模型能更好地模拟风功率随机特性,提供与实际发生的风功率相近的调度方案,从而合理地规避风电接入电网的风险,提高风电的消纳能力。

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.

A NEW MODELING METHOD FOR MACHINE-FOUNDATION COUPLING SYSTEM AND ITS APPLICATION TO THE CONTROL OF POWER FLOW

A new concept, namely, the equivalent mobility matrix of coupling subsystem is proposed, and the corresponding threesubsystem coupling progressive approach is explored. With the new efficient approach presented, the complexity in dealing with a more complicated dynamic coupling system is greatly reduced. The new modeling method is then combined with the theory of power flow to investigate the dynamics of the overall non rigid isolation system from the viewpoint of energy. The interaction between the resilient machine of its main modes and the resonant behavior of the flexible foundation on power flow transmission is studied. Taking a machine tool mounted on a multi story working plant as an example, the dynamic characteristics of the machine foundation coupling system are analyzed, and their effects on power flow transmission are revealed under various service frequency bands. Some advisable control strategies and the design principle for machinery mounted on flexible structure are proposed.

Simultaneous One-Step Approximations of Real and Reactive Power Flow

This paper presents two new non-iterative approximations of the power flow in a network. Real and reactive power are simultaneously modelled in complex equations. Also, resistances are not set to zero. This is a generalization of the DC approximation, where only real power is modelled with zero line resistance. Hence the proposed approximations are more accurate than the DC approximation. The voltage lag over a link in a short, low voltage, network link is ten times as accurate as with the DC approximation. In the Appendix a new mathematical constant is introduced.

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。

PSASP和PowerFactory变压器模型的对比

电力系统分析综合程序PSASP(power system analysis software package)和PowerFactory是目前广泛采用的电力系统分析软件,也是重庆大学电气工程学院"电力系统稳态分析"课程的实验教学工具软件。然而学生在实验中发现,对于同一算例,两个软件的潮流计算结果并不一致。分析表明,结果不一致的原因在于两个软件所用变压器模型存在差异。为此,本文从变压器参数计算方法、对励磁支路的处理等方面,对PSASP和PowerFactory的双绕组/三绕组变压器模型进行对比分析,并提出使两个软件潮流结果差异尽可能小的参数及控制选项设置方法。本文用两个简单算例验证了对比分析结果的有效性。

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.

Numerical simulation of mud-flows impacting structures

The study of the interaction of mud-flows with obstacles is important to define inundation zones in urban areas and to design the possible structural countermeasures. The paper numerically investigates the impact of a mud-flow on rigid obstacles to evaluate the force acting on them using two different depth-integrated theoretical models, Single-Phase Model(SPM) and Two-Phase Model(TPM), to compare their performance and limits. In the first one the water-sediment mixture is represented as a homogeneous continuum described by a shearthinning power-law rheology. Alternatively, the twophase model proposed by Di Cristo et al in 2016 is used, which separately accounts for the liquid and solid phases. The considered test cases are represented by a 1D landslide flowing on a steep slope impacting on a rigid wall and a 2D mud dam-break flowing on a horizontal bottom in presence of single and multiple rigid obstacles. In the 1D test case, characterized by a very steep slope, the Two-Phase Model predicts the separation between the two phases with a significant longitudinal variation of the solid concentration. In this case the results indicate appreciable differences between the two models in the estimation of both the wave celerity and the magnitude of the impact, with an overestimation of the peak force when using the Single-Phase Model. In the 2D test-cases, where the liquid and solid phases remain mixed, even if the flow fields predicted by the two models present some differences, the essential features of the interaction with the obstacles, along with the maximum impact force, are comparable.

计及低电压穿越及故障全过程动态的双馈风电场等值方法

在分析双馈感应发电机(DFIG)故障各阶段动态的基础上,提出了一种计及低电压穿越控制的双馈风电场等值方法。首先,讨论了低电压穿越控制策略,给出了含双馈风电场的电力系统故障稳态潮流计算方法。在考虑电压暂态过程的条件下,分析了外部系统短路故障后DFIG转子电流的变化机理,指出电压跌落深度及风电功率是影响短路电流的主要因素,可根据动作分界线判断撬棒是否动作。然后,根据初始风速及撬棒状态将风电场中的DFIG分为3群,并对等值DFIG及集电网络进行聚合。为提高等值模型在恢复阶段的精度,根据故障稳态电压对双馈风电场功率恢复曲线进行预估,并在此基础上对等值DFIG恢复速率进行分段修正。最后,对含双馈风电场的算例系统进行了等值计算。仿真结果表明,等值模型较好地保持了原系统在故障各阶段的动态,在保持较高精度的前提下有效简化了系统,提高了计算速度。

基于电压补偿的双端直流配电网电压就地协调控制

双端直流配电网是一种双端电源供电的网络结构,可为直流负荷提供更加稳定和可靠的电源电压。然而,负荷的功率波动和不平衡使线路电压跌落增大,可能导致直流负荷的电压不平衡度和电压偏差指标越限,影响直流负荷的正常运行。文中基于电压源型换流器(VSC)外环电压控制,考虑中线电压补偿,提出基于电压补偿等效模型的直流配电网电压偏差及不平衡度联合抑制策略,实现直流配电网电压就地协调控制。首先,建立双端直流配电网潮流模型,将VSC电压下垂控制引入潮流模型,分析不同控制策略下的电压偏差和不平衡度的特性。其次,在此基础上,以电压最低点为分点获得双端电源供电回路压降的简化等效模型,并利用最小二乘法实现等效阻抗参数辨识,构建双端直流配电网的电压补偿等效模型。以参数辨识结果作为电压外环控制输入,提出考虑中线电压补偿的双端直流配电网电压就地协调控制策略。最后,在MATLAB/Simulink中搭建仿真模型,验证了双端直流配电网潮流模型的正确性和控制策略的有效性。

Integrated Model for Resilience Evaluation of Power-Gas Systems Under Windstorms

Integrated power-gas systems(IPGS)have developed critical infrastructure in integrated energy systems.Moreover,various extreme weather events with low probability and high risk have seriously affected the stable operation of IPGSs.Due to close interconnectedness through coupling elements between the power system(PS)and natural gas system(NGS)when a disturbance happens in one system,a series of complicated sequences of dependent events may follow in another system.Especially under extreme conditions,this coupling can lead to a dramatic degradation of system performance,resulting in catastrophic failures.Therefore,there is an urgent need to model and evaluate resilience of IPGSs under extreme weather.Following this development trend,an integrated model for resilience evaluation of IPGS is proposed under extreme weather events focusing on windstorms.First,a framework of IPGS is proposed to describe states of the system at different stages under disaster conditions.Furthermore,an evaluation model considering cascading effects is used to quantify the impact of windstorms on NGS and PS.Meanwhile,a Monte Carlo simulation(MCS)technique is utilized to characterize chaotic fault of components.Moreover,time-dependent nodal and system resilience indices for IPGS are proposed to display impacts of windstorms.Numerical results on the IPGS test system demonstrate the proposed methods.

An Efficient Hybrid TLBO-PSO Approach for Congestion Management Employing Real Power Generation Rescheduling

In the present deregulated electricity market, power system congestion is the main complication that an independent system operator (ISO) faces on a regular basis. Transmission line congestion trigger serious problems for smooth functioning in restructured power system causing an increase in the cost of transmission hence affecting market efficiency. Thus, it is of utmost importance for the investigation of various techniques in order to relieve congestion in the transmission network. Generation rescheduling is one of the most efficacious techniques to do away with the problem of congestion. For optimizing the congestion cost, this work suggests a hybrid optimization based on two effective algorithms viz Teaching learning-based optimization (TLBO) algorithm and Particle swarm optimization (PSO) algorithm. For binding the constraints, the traditional penalty function technique is incorporated. Modified IEEE 30-bus test system and modified IEEE 57-bus test system are used to inspect the usefulness of the suggested methodology.

Investigation on Numerical Modeling of Water Vapour Condensation from a Flue Gas with High COR2R Content

In this paper, condensation of water vapor from a mixture of COR2R/HR2RO is studied numerically. To simplify the study and focus on the physical model, a simple vertical plate was chosen. Two condensation models are developed and numerical approach is considered to implement these models. The main objective in the cur-rent paper was to study the capability of numerical modeling in prediction of complex process. Results showed that developed condensation models in combination with numerical approach can predict the trends in condensation behavior of binary mixture very well. Results from this study can be developed further to be used in design of condensers which are suitable for oxy-fuel power plants.

Modeling Simulation Technology Research for Distribution Network Planning

This paper proposes to use the power system simulation software CYME to plan, model and simulate for an actual distribution network for improving the reliability and efficiency, enhancing the efficiency and capacity, simulating the abnormal condition of distribution network, and presenting operation program of safe, reliable and having simulation record statements. The modeling simulation results show that the software module has lots of advantages including high accuracy, ideal reliability, powerful practicality in simulation and analysis of distribution network, it only need to create once model, the model can sufficiently satisfy multifarious types of simulation analysis required for the distribution network planning.

抽蓄电站无压隧洞交叉区体型优化试验研究

交叉无压隧洞交汇区域水流的水力特性复杂,无压隧洞交叉区体型及交汇口水流水力特性的研究对确保水利枢纽的安全运行具有重要的工程意义。基于物理模型试验,对某抽水蓄能电站下水库高落差泄洪排沙洞和放空洞交叉区体型进行优化,最终确定圆弧连接+交叉角21°的交叉区体型。对比分析圆弧连接+交叉角21°的交叉区优化体型下特征试验工况的水力特性。结果表明,6种特征试验工况下,泄洪排沙洞和放空洞交叉口及下游均为急流,明流泄洪且流态较稳定,均在交汇口下游右边直墙处形成最大水深,水深低于直墙高度,满足水面线不宜超过直墙范围的要求。

基于线性化潮流模型的配电网电压无功控制策略

针对现有基于二阶锥松弛的电压无功控制模型无法以电压波动为目标且求解速度较慢等问题,文中提出了一种基于线性化潮流模型的配电网电压无功控制策略。基于支路潮流方程建立了包含有载调压分接头、电容器组和光伏逆变器等调控手段的电压无功控制模型,并将其离散变量松弛为连续变量,以形成二阶锥规划。进一步以二阶锥规划所得结果为基准点构造线性化潮流模型,并以电压波动最小为目标,将连续变量还原为离散变量。最后基于改进的IEEE-33节点测试系统进行了仿真,仿真结果表明所提出的线性化潮流模型具有较高的精度和更快的求解速度,能够适用于配电网实时电压无功控制。

涡轮动力模拟器甩油盘热流模型与流场特性研究

甩油盘作为涡轮动力模拟器(TPS)的重要零件,能有效地促进模拟器内循环系统润滑油的回流,提高轴承的润滑性并降低系统温升,为整机安全可靠运行提供了基础性保障。为了解决TPS内循环系统润滑油的回流问题,对TPS甩油盘及其内部循环流道进行了研究。首先,确定了涡轮动力模拟器轴承发热量及散热系数随转速的变化、甩油盘内部流体控制方程和边界条件;然后,构建了一类TPS甩油盘及其内部循环流道的完整内循环热流模型,并对比了轴承处温度仿真结果与实验结果以确保模型的合理性;最后,数值仿真得到了不同转速下内部循环流道的温度场、压力场和速度场。研究结果表明:转速增加能显著引发系统内最高温度上升,甩油盘作用下的内循环流场温度变化较为平稳,典型工况条件下仿真与实验得到的最高温度相对误差最大为12.3%,表明了热流模型的合理性。研究结果对于指导TPS甩油盘结构设计和提高整机运行安全稳定性具有重要的价值。

应用图论建模输电网的电力现货市场出清模型

电力现货市场优化出清模型的难点是考虑安全约束的机组组合(security constrained unit commitment,SCUC)模型。构建一个好的SCUC模型以提升求解速度是长期以来的研究热点。随着省电力系统规模的不断发展,以及国内省间电力现货市场的运行,现货市场对于出清模型的求解效率需求更为突出。该文对机组组合模型的研究历程进行详细综述,总结提出机组运行出力约束、出力上限约束、爬坡约束强化建模的机组运行模型;基于图论在线性最优潮流计算中的应用,构建输电网的环流潮流计算模型并引入SCUC模型,最终构建了一套可进一步提升求解效率的电力现货市场出清模型。最后通过多个大规模算例的计算分析表明,所提模型在保证不损失求解精度的同时,可有效提升求解效率,且对于阻塞频发的电力系统,优越性更为明显。

基于数据潮流模型的高比例光伏配电网三相不平衡优化

随着分布式光伏的大规模接入,配电网固有的三相不平衡问题日益严重,给系统的电能质量、经济运行等带来不利影响。此外,高比例光伏的接入使得配电网的物理结构和运行方式更加复杂多变,导致当前依赖精确拓扑结构和线路参数的三相不平衡优化方法难以应用。因此,提出一种基于数据潮流模型的高比例光伏配电网三相不平衡优化方法。首先,采用基于双阶段注意力机制的循环神经网络方法建立数据潮流模型,拟合三相潮流约束中变量之间的函数关系。同时,提出图特征嵌入的方法将部分已知的拓扑信息嵌入到数据潮流模型中以提高拟合精度。其次,以训练后的数据潮流模型为基础重建配电网三相不平衡优化模型。最后,通过条件梯度下降方法求解该模型,以修改的IEEE33节点配电网络为例,验证了所提方法的有效性。