DC FLOW SUPPRESSION IN A SINGLE-STAGE G-M TYPE PULSE TUBE COOLER

An experimental investigation on DC flow suppression in a single-stage G-M type pulse tube cooler is made. The influence of DC flow induced by the introduction of the double-inlet on the refrigeration performance of the cooler is experimentally examined. Two parallelplaced needle valves with an opposite flow direction called as double-valved configuration, instead of conventional single-valved configuration as the double-inlet is used to reduce the DC flow. With the double-valved configuration, the minimum temperatures of 18.4 K and 14.7 K, and the cooling powers of 11.5 W and 29.5 W are also obtained by RW2 and CP4000, respectively.

Automated Two-stage Conversion of Hourly Optimal DC Flow Solution to AC Power Flow

Conversion of hourly dispatch cases derived using DC optimal power flow(DCOPF)to AC power flow(ACPF)case is often challenging and requires arduous human analysis and intervention.This paper proposes an automated two-stage approach to solve ACPF formulated from DCOPF dispatch cases.The first stage involved the use of the conventional Newton Raphson method to solve the ACPF from flat start,then ACPF cases that are unsolvable in the first stage are subjected to a hotstarting incremental method,based on homotopy continuation,in the second stage.Critical tasks such as the addition of reactive power compensation and tuning of voltage setpoints that typically require human intervention were automated using a criteriabased selection method and optimal power flow respectively.Two datasets with hourly dispatches for the 243-bus reduced WECC system were used to test the proposed method.The algorithm was able to convert 100%of the first set of dispatch cases to solved ACPF cases.In the second dataset with suspect dispatch cases to represent an extreme conversion scenario,the algorithm created solved ACPF cases that satisfied a defined success criterion for 77.8%of the dispatch cases.The average run time for the hotstarting algorithm to create a solved ACPF case for a dispatch was less than 1 minute for the reduced WECC system.

Model Predictive Control Strategy of Multi-Port Interline DC Power Flow Controller

There are issues with flexible DC transmission system such as a lack of control freedom over power flow.In order to tackle these issues,a DC power flow controller(DCPFC)is incorporated into a multi-terminal,flexible DC power grid.In recent years,a multi-port DC power flow controller based on a modular multi-level converter has become a focal point of research due to its simple structure and robust scalability.This work proposes a model predictive control(MPC)strategy for multi-port interline DC power flow controllers in order to improve their steady-state dynamic performance.Initially,the mathematical model of a multi-terminal DC power grid with a multi-port interline DC power flow controller is developed,and the relationship between each regulated variable and control variable is determined;The power flow controller is then discretized,and the cost function and weight factor are built with numerous control objectives.Sub module sorting method and nearest level approximation modulation regulate the power flow controller;Lastly,theMATLAB/Simulink simulation platformis used to verify the correctness of the establishedmathematicalmodel and the control performance of the suggestedMPC strategy.Finally,it is demonstrated that the control strategy possesses the benefits of robust dynamic performance,multiobjective control,and a simple structure.

The third type DC flow in pulse tube cryocooler

New phenomena discovered in the experimental research of the ultra-high frequency pulse tube cryocooler were presented.The cause of the new phenomena was analyzed and the third type DC flow was discovered in the pulse tube cryocooler.The third type DC flow not only deteriorated cooling capacity but also led to temperature instability of the pulse tube cryocooler.From the fluid network theory and the simple regenerator model,the root of the third type DC flow was concisely investigated in theory. The asymmetric resistance of oscillating flow in pulse tube cryocooler was the key mechanism of the third type DC flow.Some suppression methods were briefly discussed.

Fluid Flow Modeling of Arc Plasma and Bath Circulation in DC Electric Arc Furnace

A mathematical model describing the flow field, heat transfer and the electromagnetic phenomenon in a DC electric arc furnace has been developed. First the governing equations in the arc plasma region are solved and the calculated results of heat transfer, current density and shear stresses on the anode surface are used as boundary conditions in a model of molten bath. Then a two-dimensional time-dependent model is used to describe the flow field and electromagnetic phenomenon in the molten bath. Moreover, the effect of bottom electrode diameter on the circulation of molten bath is studied.

Coupled Modeling of Electromagnetic Fleld,Fluid Flow,Heat Transfer and Solidification During Conventional DC Casting and Low Ftequency Electrmagnetic Casting of 7xxx Aluminum Alloys

A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for the calculation of the electromagnetic field and the latter for the calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from two 7XXX aluminum alloy billets of 200mm diameter, cast during the conventional DC casting and the LFEC casting processes. In addition, a measurement of the sump shape of the billets were carried out by using addition melting metal of Al-30%Cu alloy into the billets during casting process. There was a good agreement between the calculated results and the measured results. Further, comparison of the calculated results during the LFEC process with that during the conventional DC casting process indicated that velocity patterns, temperature profiles and the sump depth are strongly modified by the application of a low frequency electromagnetic field during the DC casting.

Effects of Gas Flow Rate on the Discharge Characteristics of a DC Excited Plasma Jet

A direct current（DC） source excited plasma jet consisting of a hollow needle anode and a plate cathode has been developed to form a diffuse discharge plume in ambient air with flowing argon as the working gas.Using optical and electrical methods,the discharge characteristics are investigated for the diffuse plasma plume.Results indicate that the discharge has a pulse characteristic,under the excitation of a DC voltage.The discharge pulse corresponds to the propagation process of a plasma bullet travelling from the anode to the cathode.It is found that,with an increment of the gas flow rate,both the discharge plume length and the current peak value of the pulsed discharge decrease in the laminar flow mode,reach their minima at about1.5 L/min,and then slightly increase in the turbulent mode.However,the frequency of the pulsed discharge increases in the laminar mode with increasing the argon flow rate until the argon flow rate equals to about 1.5 L/min,and then slightly decreases in the turbulent mode.

一种双向部分隔离型四端口DC-DC变换器的研究

为减少家庭直流微电网中变换器的数量,提出了一种双向部分隔离型四端口直流变换器及其控制策略。变换器原边采用两个双向Buck-Boost电路与全桥变换器的桥壁开关管复用,构成两输入的双向交错Buck-Boost电路,副边采用半桥整流电路与同步Buck电路结合,形成高、低压两输出端口,并采用控制器变量竞争的方式实现变换器控制策略的切换。该四端口变换器(four-port converter,FPC)可以同时满足多电压等级的输入/输出,且功率能够双向流动,对比其他FPC,具有较高的功率密度和拓扑结构对称等优点。最后,在Simulink软件中搭建了仿真模型,并进行详细的试验分析。结果验证了理论分析的正确性以及控制策略的有效性。

含VSC-MTDC的交直流系统潮流算法

多端柔性直流输电系统(voltage source converter based multi-terminal direct current system,VSC-MTDC)是在两端直流输电基础上发展而来的直流输电系统,可靠性高、适用于海上风电并网等场景,相应的控制策略更加多样,其潮流模型也更加复杂。该文分析VSC换流站和MTDC的稳态模型,研究可适用于VSC-MTDC的不同拓扑和连接方式的潮流模型;研究多端直流各种控制策略潮流计算模型的不同点并推导出其方程。在此基础上,提出一种兼具统一迭代法和交替迭代法优点的含VSC-MTDC交直流系统潮流算法,给出初值和边界条件求解方法,对于不同直流拓扑和交流系统都能够进行求解。最后通过2个实际算例验证该文潮流模型的有效性和收敛性,对于不同控制方式、不同运行场景和直流拓扑都能够迅速、稳定收敛。

基于DCS的EAST低温系统预冷过程自动控制

为避免热应力对EAST托卡马克装置的损坏,超导磁体与冷屏的300—80 K预冷过程需要严格控制降温温差;同时低温系统还需提供合适的流量与压降,以保证各冷质部件同步快速降温。通过低温控制流程分析,明确了预冷控制回路与控制需求,设计了预冷操作模式及其顺序控制流程。针对预冷过程中温差-压降耦合问题,设计了分阶段的解耦控制方案。以上控制策略在低温DCS中组态实现,经两轮降温实验运行验证,解耦控制稳定,实现了快速同步降温。预冷过程自动控制取代了持续十几天的预冷手动操作,系统的自动化程度得到了极大提升。

AC/DC系统潮流计算的部分直流变量消除法

为克服AC/DC系统的潮流计算方法中的变量消除法的不足,提出了部分直流变量消除法.该方法的模型中将换流器等效为依赖于换流器端交流电压和控制角的PQ负荷.计算时,只需规定换流器直流侧的无功功率,而且当直流系统控制方式发生变化后不需重新推导Jacobian矩阵中的偏导公式.数值算例表明该方法具有较高的灵活性,与变量消除法相比计算效率可提高5%左右.

基于DCS的污水处理自动控制系统研究

结合危废处置行业污水处理工艺特点,依托基于分布式控制系统的网络布局,提出了一种污水处理自动控制系统实现的方案,用以实现污水的自动化控制。借助计算机技术的优势,污水处理自动控制系统在节约人力成本的同时,能够实现对污水处理过程的可控性管理,提高污水处理效果。

基于连续潮流法的含双端VSC-HVDC交直流系统负荷裕度分析

为了分析含双端VSC-HVDC交直流系统的静态电压稳态特性,结合交替求解法和连续潮流法给出一种交直流连续潮流法。根据初始输入得到初始解确定负荷增长方向,引入负荷裕度参数。通过调节VSC-HVDC的控制策略,最终得到系统不同情况下的负荷裕度,采用左特征向量乘子法对系统进行负荷裕度灵敏度计算。对含双端VSC-HVDC的IEEE39节点系统和IEEE118节点系统进行建模仿真,得出了系统负荷裕度以及负荷裕度灵敏度近似线性的变化规律。直流线路功率流向对系统负荷裕度的影响相反,验证了方法的有效性。

电厂DCS锅炉给水流量计算中存在的问题及处理

针对某300 MW亚临界国产机组给水流量计算中存在的问题进行了阐述,分析了计算结果偏大的原因,并提出了通用的简化计算公式。经处理后,计算精度能够满足现场要求,又便于在DCS中实施。

DCS主蒸汽流量计算模型的改进

基于对DCS主蒸汽流量原有模型的分析,对原模型存在的流量计算偏差大等问题采用第1级抽汽温度测量值替代调节级后温度进行修正计算,并取额定负荷运行时循环效率试验的第1级抽汽温度值(387℃)作为基准温度等,进行上述改进后,机组各负荷工况下主蒸汽流量模型计算值与实际值的最大绝对偏差均小于1.95%;主蒸汽流量模型参数随机组负荷变化平稳。

舰船电力系统自组织临界特性分析

基于自组织临界理论,以直流潮流为基础,建立了舰船电力系统连锁停电的OPA模型。通过OPA模型模拟了舰船电力系统发生连锁故障的过程并揭示出舰船电力系统发生大停电事故的本质;研究了线路可靠性和线路容量对系统停电分布的影响,结果表明,增强线路可靠性和提高线路容量有利于系统抵御连锁故障。此外,对比环形舰船电网结构和辐射型舰船电网结构的停电规模分布,从系统自组织临界特性的角度验证环形舰船电网结构可靠性更高。

DC-CIK细胞免疫治疗联合化疗对卵巢癌免疫功能的影响

目的 探讨细胞因子诱导的杀伤（cytokine-induced killer,CIK）细胞、树突状细胞（dendritic cells,DC）免疫治疗联合化疗对晚期卵巢癌患者外周血淋巴细胞亚群的影响,并评估其治疗效果. 方法 选取2011-09～2013-08就诊于新乡市中心医院的62例卵巢上皮性恶性肿瘤患者,其中30例患者采用DC-CIK联合化疗[紫杉醇（taxel）＋卡铂（cisplatin）]为联合治疗组;选取同期进行单纯化疗的32例患者为单纯化疗组.3周为1个周期,3周期后评价疗效.治疗结束1周后采用流式细胞仪检测外周血CD3＋、CD3＋ CD4＋、CD4＋/CD8＋、CD4＋ CD25＋T调节性T细胞、NK细胞的变化. 结果 每位患者治疗3个周期后,联合治疗组患者外周血CD3＋、CD3＋ CD4＋、CD4＋/CD8＋、NK水平明显高于单纯化疗组（P＜0.05）.联合治疗组患者的客观缓解率为85.7％,显著高于单纯化疗组的56.5％ （P ＜0.05）.联合治疗组患者的不良反应（包括骨髓抑制、肝功能损害）明显轻于单纯化疗组（P＜0.05）,联合治疗组患者治疗后体力状况评分较单纯化疗组改善明显. 结论 DC-CIK细胞免疫治疗联合化疗能提高卵巢癌患者的细胞免疫功能,且安全有效.

钒液流储能变流器双向DC/DC四阶段控制策略

针对储能系统中钒电池端电压及充放电控制模式变换对钒电池安全运行的影响。以钒电池的端电压和荷电状态值为充放电约束条件,提出首次充电时采用小电流充电法激活电池,然后采用恒电流、恒功率、恒压和涓流4种控制策略分阶段对钒电池进行充放电。经仿真及5 kW钒液流储能系统实验,该控制策略减小了钒电池端电压及充放电控制模式变换对钒电池安全运行的影响,验证了所提双向DC/DC四阶段控制策略的可行性。

考虑运行损耗和功率裕度的VSC-MTDC系统改进优化下垂控制策略

不当的直流电压下垂系数易造成多端柔性直流输电(VSC-MTDC)系统运行损耗增加或部分换流站满载,为此提出了1种考虑网络损耗和功率裕度的改进优化下垂控制策略。分析了影响直流网络潮流的因素,在考虑直流线路电压降的情况下,推导出了换流站间功率分配与下垂系数的关系式。提出了直流网络潮流优化计算方法,并得出了各换流站最优下垂系数。以换流站优化下垂特性为基础,设置直流电压拐点,综合考虑直流系统运行损耗和换流站功率裕度,提出了改进的优化下垂控制策略。在PSCAD/EMTDC仿真软件中搭建6端柔性直流输电系统仿真模型,对3种下垂控制策略下系统的运行特性进行了仿真分析,结果表明:常规下垂控制按换流站额定容量分配功率,优化下垂控制考虑直流网络损耗,改进优化下垂控制兼顾系统运行损耗和换流站设备使用率。仿真结果与理论分析一致,验证了所提改进控制策略的有效性和可行性。

基于ADMM的含风电场系统分布式DC-OPF计算

电网中的不同电力公司所管辖子系统具有相互独立且互联的特点,各子系统之间的互联给电网的分布式计算带来一定挑战,如何实现大系统的分布式计算备受关注。提出基于交替方向乘子法(alternating directionmethod of multipliers,ADMM)的含风电场系统分布式直流最优潮流(direct current optimal power flow,DC-OPF)计算模型,该模型考虑风电并网对系统分布式DC-OPF的影响,采用分解协调法实现系统的分区过程,通过引入全局变量处理边界节点问题,在信息传递过程中无需中心处理系统,只在相邻子区域之间进行复制边界节点的信息传递以减少信息通信量,实现系统的全分布式DC-OPF计算。以6节点系统、IEEE-39节点系统分析全局变量的个数对迭代收敛的影响,并讨论风电并网对优化收敛的影响,最后通过仿真验证该文所提模型的准确性和有效性。