Simulations of the Allowable Load Current of the Overhead Lines in the Latvian Power Network

This paper considers the influence of changes of the transmission lines of permissible load current depending on conductor and ambient temperatures, climate conditions. The theoretical background of the allowable conductor temperature as well as load current determination principles are proposed. On one hand, the principles are based on mechanical limitations; on the other hand, they are based on thermal limitations. The simulation tasks were based on specific data information of three existing overhead lines of Latvian power system as well as the planned 330 kV overhead line. Moreover, the special thermovision device was used for precious determination of conductor temperature of the existing transmission lines. The simulation results of the obtained data are reviewed in the paper.

Robust Nonlinear Current Sensorless Control of the Boost Converter with Constant Power Load

The boost converter feeding a constant power load (CPL) is a non-minimum phase system that is prone to the destabilizing effects of the negative incremental resistance of the CPL and presents a major challenge in the design of stabilizing controllers. A PWM-based current-sensorless robust sliding mode controller is developed that requires only the measurement of the output voltage. An extended state observer is developed to estimate a lumped uncertainty signal that comprises the uncertain load power and the input voltage, the converter parasitics, the component uncertainties and the estimation of the derivative of the output voltage needed in the implementation of the controller. A linear sliding surface is used to derive the controller, which is simple in its design and yet exhibits excellent features in terms of robustness to external disturbances, parameter uncertainties, and parasitics despite the absence of the inductor’s current feedback. The robustness of the controller is validated by computer simulations.

Research on the Dynamic Response of Submerged Floating Tunnels to Wave Currents and Traffic Load

Submerged floating tunnel(SFTs)are typically subjected to complex external environmental and internal loads such as wave currents and traffic load.In this study,this problem is investigated through a finite element method able to account for fluid-structure interaction.The obtained results show that increasing the number of vehicles per unit length enhances the transverse vibrational displacements of the SFT cross sections.Under ultimate traffic load condition,one-way and two-way syntropic distributions can promote the dynamic responses of SFTs whereas two-way reverse distributions have the opposite effect.

Dynamics and stabilization of peak current-mode controlled buck converter with constant current load

The discrete iterative map model of peak current-mode controlled buck converter with constant current load（CCL）,containing the output voltage feedback and ramp compensation, is established in this paper. Based on this model the complex dynamics of this converter is investigated by analyzing bifurcation diagrams and the Lyapunov exponent spectrum. The effects of ramp compensation and output voltage feedback on the stability of the converter are investigated. Experimental results verify the simulation and theoretical analysis. The stability boundary and chaos boundary are obtained under the theoretical conditions of period-doubling bifurcation and border collision. It is found that there are four operation regions in the peak current-mode controlled buck converter with CCL due to period-doubling bifurcation and border-collision bifurcation. Research results indicate that ramp compensation can extend the stable operation range and transfer the operating mode, and output voltage feedback can eventually eliminate the coexisting fast-slow scale instability.

Experimental study on bed-load sediment transport under irregular wave and current combined flow

Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave -current coexistent field. Testing conditions include three interaction angles 0', 45', 90' and two kinds of median sizes (0.38 and 1.10 mm). The results of transport rate show that the net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress of waves, mean shear stress of current and the grain size.

A DISCUSSION ON CURRENTS AND SUSPENDED LOAD TRANSPORT IN SURF ZONE

In this paper, the distribution characteristics of the breaking wave current and suspended load transport in the surf zone are discussed in main. Based on the measured data of the waves, the form of breaking wave, the breaking wave current and the sediment concentration of suspended load in the offshore surf zone near Nouakchott, the Islamic Republic of Mauritania, the author has analized the law governing the distribution of longshore current and sediment concentration of suspended load by means of statistical method, and presented a calculation method for the longshore sediment transport in offshore surf zone.

Effects of drive current rise-time and initial load density distribution on Z-pinch characteristics

A two-dimensional, three-temperature radiation magneto-hydrodynamics model is applied to the investigation of evolutional trends in x-ray radiation power, energy, peak plasma temperature and density as functions of drive current rise-time and initial load density distribution by using the typical experimental parameters of tungsten wire-array Z- pinch on the Qiangguang-I generator. The numerical results show that as the drive current rise-time is shortened, x-ray radiation peak power, energy, peak plasma density and peak ion temperature increase approximately linearly, but among them the x-ray radiation peak power increases more quickly. As the initial plasma density distribution in the radial direction becomes gradually flattened, the peak radiation power and the peak ion-temperature almost exponentially increase, while the radiation energy and the peak plasma density change only a little. The main effect of shortening drive current rise-time is to enhance compression of plasma, and the effect of flattening initial load density distribution in the radial direction is to raise the plasma temperature. Both of the approaches elevate the x-ray peak radiation power

Analysis of load status and management strategies of main caregivers of patients with malignant tumors of digestive tract

Caregiver load refers to the subjective and objective negative impact of caregivers in the care of patients,and excessive load will have a serious impact on patients and caregivers themselves and can reduce their quality of life.For the main caregivers,it not only needs to care for the patients in life and daily life,but also needs to pay the cost of treatment for the patients,coupled with the need to carry out their own original work,life,etc.excessive life pressure,economic pressure,work pressure,emotional pressure,etc.lead to heavy load of the main caregivers,which can easily cause caregivers to have different degrees of psychological problems,which will cause serious adverse effects on the caregivers themselves and cancer patients,not conducive to the construction of a harmonious family and society.This article analyzes the current situation of primary caregiver burden in patients with gastrointestinal malignant tumors,analyzes its influencing factors,and specifies specific treatment strategies.It is hoped to provide scientific guidance for later related research and application.

Dynamic Response Analysis of Risers Subjected to Combined Wave and Current Loading

A dynamic response analysis in the frequency domain is presented for risers subjected to combined wave and current loading. Considering the effects of current, a modified wave spectrum is adopted to compute the linearized drag force. An additional drag force convolution term is added to the linearized drag force spectrum, therefore the error is reduced which arises from the truncation of higher order terms in the drag force auto-correlation function. An expression of linearized drag force spectrum is given taking the relative velocity into account. It is found that the additional term is a fold convolution integral. In this paper dynamic responses of risers are investigated, while the influence of floater motion on risers is considered. The results demonstrate that the accuracy of the present method reaches the degree required in time domain analysis.

含逆变型分布式电源和分支负荷的配电网自适应电流差动保护

电流差动保护具有良好的选择性和灵敏性。但是,逆变型分布式电源(inverter-interfaced distributed generator,IIDG)和分支负荷接入改变了配电网的故障特性,现有配电网的电流差动保护面临拒动或误动的风险。为解决以上问题,该文在计及P/Q控制的IIDG和分支负荷的故障等值建模基础上,从故障点、IIDG和分支负荷的相对位置出发,挖掘配电网线路两端正序电流差的幅值特征以及正序电流故障分量的相位特征。在此基础上,提出一种正序电流幅值与故障分量相角阈值配合的双比例制动系数自适应差动保护方案,并且利用幅相平面分析所提保护判据的可靠性和灵敏性。最后通过PSCAD/EMTDC验证了所提保护方案的有效性,仿真结果表明该方案适应不同故障类型、位置和过渡电阻,且不受IIDG以及分支负荷接入的影响。

双路电源的主动均流电路系统研究

广泛使用的低成本电源管理芯片或直流电源模块通常并未集成输出均流控制功能,因此不能直接并联输出使用。而使用特殊的电源管理芯片或是额外的均流控制电路会提高电源电路的复杂程度,造成电路成本的提高。针对此应用场景,提出了一种具有主动均流功能的双路电源开关,作为负载开关或电源多路复用器应用于电路之中,利用开关电流的方法均分输出电流,在几乎不增加电路成本的同时对两路电源进行均流。阐述了所提双路电源开关的工作原理与参数设计方法,并通过仿真与实验证明了所提方法的正确性与可行性。

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。

地铁车站弱电设备间设备发热量确定方法

介绍了一种地铁车站弱电设备间设备发热量确定新方法,该方法利用弱电设备发热量实测数据与模型预测数据相互验证,可以有效提高弱电设备发热量确定结果的准确性。研究了室内气温、地铁是否运营、设备额定功率和车站类型等因素对设备发热量的影响。研究结果表明:基于间接测量和预测模型的地铁车站弱电设备间设备发热量确定方法可以提高和保障设备发热量计算结果的准确性;室内气温会显著影响设备外表面和围护结构内表面温度及围护结构内表面热流密度,但对设备外表面热流密度的影响较小;地铁是否运营对弱电设备间设备发热量有较大影响,地铁运营期间设备发热量大于非运营期间;设备额定功率对弱电设备间设备发热量峰值有较大影响,车站类型和建筑面积对设备发热量峰值的影响很小。

基于中性线电流离散分析治理三相负荷不平衡

当三相负荷不平衡时,必然会引起中性线电流的产生。针对三种不同三相负荷不平衡条件下中性线电流的变化情况,建立与之对应的三相负荷不平衡度算法模型。采用中性线电流的离散分析建立三相负荷不平衡度算法,作为三相负荷不平衡治理的有效判据,结合试验分析,得到了三相负荷不平衡度与中性线电流的变化规律,并应用于低压供配电系统三相负荷不平衡的治理分析。结果表明:所提三相负荷不平衡度算法对低压供配电系统三相负荷不平衡的治理具有较强的实用性。提出的以三相负荷不平衡度为自适应变量,以中性线电流为过程监测量,采用有功调配与无功补偿相结合策略,能够有效反映三相负荷不平衡的治理情况。

基于动车组负荷电流特征的电流增量保护改进方案

电流增量保护由于整定值过高可能在牵引网发生高阻接地故障时拒动,受动车组负荷特殊工况和牵引网结构的影响可能误动作。为了分析电流增量保护拒动和误动的原因,有效辨识高阻接地故障电流和动车组负荷电流,在高速铁路牵引变电所馈线和动车组上进行电流录波测试,分析牵引变电所馈线电流和单列动车组负荷电流的电流增量和高次谐波增量特征及其形成原因,提出一种带高次谐波增量闭锁的电流增量保护改进方案,并对电流增量整定值和高次谐波增量闭锁整定值提出建议。基于现场高阻接地故障录波和动车组负荷测试电流波形分析以及基于MATLAB/Simulink的含动车组的牵引供电系统建模仿真分析,验证了所提改进方案在动车组负荷与高阻接地故障辨识方面的有效性。

基于负荷电流的综合管廊电缆发热量计算

综合管廊属于密闭型地下构筑物,廊内敷设的电缆是主要的发热源。准确估计入廊电缆的发热量有助于通风设备的合理选择和工艺的科学设计,避免造成资源和成本的浪费。本文提出了基于负荷电流的电缆发热量计算方法,通过对出变电站母线段电缆进行分析,得到了更为精确的电缆负荷电流。通过计算可知,使用负荷电流进行电缆发热量计算得到的结果比使用载流量进行电缆发热量计算的结果更为准确,且明显减小,可以实现在满足规范要求和功能需要的前提下降低能耗、节约成本。

适配变压器全档位切换暂态分析的有载分接开关电路模型构建

有载分接开关(on-loadtap-changer,OLTC)是换流变压器的核心组件,其可靠切换过程关乎换流变的安全。然而目前国内在运特高压换流变用OLTC完全依赖进口,仿真获取OLTC不同运行状态的暂态特性数据是支撑OLTC关键电气参数设计与国产化制造的基础。经典的OLTC模型仅改变变压器变比或仅模拟单级档位切换过程,难以满足全档位电压调整与各级档位暂态特性数据同步获取的需求,导致OLTC设计优化、参数选型及故障分析缺乏足够的仿真数据支持。该文首先以真空OLTC为研究对象建立切换开关和极性开关等效电路模型,根据OLTC复杂的调压功能建立分层控制系统。其次,在PSCAD中搭建交流仿真系统,获取有载调压过程的暂态特性数据波形,与解析计算得到的电压和电流相比误差小于0.2%,证明该模型满足OLTC电磁暂态仿真研究的精度要求。最后,开展循环调压仿真,获得负载电压数据与波形。结果表明:该文提出的OLTC模型能够接收外部控制信号,进行全档位调压与极性转换仿真分析,能够为OLTC的调压研究、故障溯源分析和过渡电阻设计选型等提供基础模型。

基于在线特征库的非侵入式负荷特征提取方法

负荷特征是指负荷设备运行过程中具备某种统计规律的特殊标识,而包含负荷特征的数据库则是实现非侵入式负荷监测与分解的基本依据。对于纯阻性负荷设备,研究人员利用其运行状态切换过程中功率产生跃变的特点,可以准确提取相应状态下的负荷特征。然而,对非纯阻性设备,其负荷特征提取存在以下2个问题。问题1)运行状态切换过程中功率变化不显著,无法精准定位状态投切时刻点;问题2)负荷设备存在功率缓变化的运行状态,导致对应状态下的负荷特征不唯一,无法手动提取。为了解决非纯阻性设备负荷特征提取中存在的上述问题,提出一种基于在线特征库的非侵入式负荷特征提取方法,该方法分为2个阶段。第一阶段:基于负荷设备运行过程中的稳态周期电流数组建立在线特征库,通过改进Pearson相似系数构建滑窗函数,得到负荷设备运行时的周期电流数组与在线特征库的相似性,并同步判断在线特征库冗余性,实现负荷设备状态数据分割;第二阶段:计算在线特征库的特征矩阵,对特征矩阵进行K-means聚类分析,融合相似在线特征库,形成负荷设备的状态特征库,从而实现负荷设备特征电流数组的提取。在私人数据集和PLAID数据集上的测试结果证明,所提负荷特征提取方法在不同的用电场景下均有较好的鲁棒性。所提方法可大幅减少负荷特征提取阶段的人工参与,有利于缓解因负荷设备种类过多导致的负荷特征提取烦琐的问题,为后续建立负荷特征数据库提供了便利。

深中通道沉管隧道水下基槽开挖边坡稳定性分析

在沉管隧道整体施工过程中,特别是外海沉管隧道,其深基槽通常面临海流作用复杂、基槽泥沙回淤等问题,给基槽边坡的安全稳定性带来不利影响。以深中通道沉管隧道工程为背景,采用数值模拟方法,通过对边坡形态、边坡回淤物分布以及海流荷载等因素的研究,分析了在相应条件下水下基槽边坡的安全系数和破坏特性。结果表明,边坡的土体特性与几何形态、边坡回淤物的分布与厚度以及海流荷载的大小与方向的变化均会对基槽边坡的稳定性造成不同程度的影响。

瞬时电流预测的逆变器启动冲击负载的方法

针对通用逆变器启动冲击负载能力很弱的问题,此处提出一种利用瞬时负载电流预测来控制输出调制比的方法来增强逆变器启动冲击负载的能力。冲击性负载,通常是感性负载投入时会产生5~10倍的冲击电流,而通用逆变器抗冲击电流能力较弱,通常只能启动20%的额定负载。这里根据检测到的负载瞬时电流来瞬时减小逆变器的输出调制比,将负载电流控制在额定电流范围内,感性负载投入后会逐渐稳定,输出调制比也逐渐恢复到正常值,完成感性负载的启动。此方法已在油田储能电源上得到广泛应用,可将逆变器启动感性负载的能力从20%额定提高到70%额定。