Numerical study of plasmas start-up by electron cyclotron waves in NCST spherical tokamak and CN-H1 stellarator

According to the physics of tokamak start-up,this study constructs a zero-dimensional(0D)model applicable to electron cyclotron(EC)wave assisted start-up in NCST spherical torus(spherical tokamak)and CN-H1 stellarators.Using the constructed 0D model,the results obtained in this study under the same conditions are compared and validated against reference results for pure hydrogen plasma start-up in tokamak.The results are in good agreement,especially regarding electron temperature,ion temperature and plasma current.In the presence of finite Ohmic electric field in the spherical tokamak,a study on the EC wave assisted start-up of the NCST plasma at frequency of 28 GHz is conducted.The impact of the vertical magnetic field B_(v)on EC wave assisted start-up,the relationship between EC wave injection power P_(inj),Ohmic electric field E,and initial hydrogen atom density n_(H0)are explored separately.It is found that under conditions of Ohmic electric field lower than ITER(~0.3 V m^(-1)),EC wave can expand the operational space to achieve better plasma parameters.Simulating the process of28 GHz EC wave start-up in the CN-H1 stellarator plasma,the plasma current in the zerodimensional model is replaced with the current in the poloidal coil of the stellarator.Plasma startup can be successfully achieved at injection powers in the hundreds of kilowatts range,resulting in electron densities on the order of 10^(17)-10^(18)m^(-3).

Analysis of Quenching Resistor Effect to Improve Stability of TIA Circuit for APD-A Secondary Publication

In this paper,since the Avalanche Photo Diode(APD)for Light-to-Voltage LTV conversion uses a high voltage in the operating range unlike other Photo Diodes(PD),the quenching resistor must be connected in series to prevent overcurrent when using the Transimpedance Amplifier(TIA).In such a case,quenching resistance may affect the transfer function of the TIA circuit,resulting in serious stability.Therefore,in this paper,by analyzing the effect of APD quenching resistance on the voltage and current loop transfer function of TIA,we proposed a loop analysis and a method for determining the quenching resistance value to improve stability.A TIA circuit with quenching resistance was designed by the proposed method and its operational stability was verified through simulation and chip fabrication.

Numerical Simulation of a Two-Phase Flow with Low Permeability anda Start-Up Pressure Gradient

A new numerical model for low-permeability reservoirs is developed.The model incorporates the nonlinear characteristics of oil-water two-phase flows while taking into account the initiation pressure gradient.Related numerical solutions are obtained using a finite difference method.The correctness of the method is demonstrated using a two-dimensional inhomogeneous low permeability example.Then,the differences in the cumulative oil and water production are investigated for different starting water saturations.It is shown that when the initial water saturation grows,the water content of the block continues to rise and the cumulative oil production gradually decreases.

Dynamic evaluation of a scaled-down heat pipe-cooled system during start-up/shut-down processes using a hardware-in-the-loop test approach

Micro-mobile heat pipe-cooled nuclear power plants are promising candidates for distributed energy resource power genera-tors and can be flexibly deployed in remote places to meet increasing electric power demands.However,previous steady-state simulations and experiments have deviated significantly from actual micronuclear system operations.Hence,a transient analysis is required for performance optimization and safety assessment.In this study,a hardware-in-the-loop(HIL)approach was used to investigate the dynamic behavior of scaled-down heat pipe-cooled systems.The real-time features of the HIL architecture were interpreted and validated,and an optimal time step of 500 ms was selected for the thermal transient.The power transient was modeled using point kinetic equations,and a scaled-down thermal prototype was set up to avoid mod-eling unpredictable heat transfer behaviors and feeding temperature samples into the main program running on a desktop PC.A series of dynamic test results showed significant power and temperature oscillations during the transient process,owing to the inconsistency of the rapid nuclear reaction rate and large thermal inertia.The proposed HIL approach is stable and effective for further studying of the dynamic characteristics and control optimization of solid-state small nuclear-powered systems at an early prototyping stage.

3D_Multi Resistor Electric Circuit

This report addresses the issues concerning the analysis of an electric circuit composed of multiple resistors configured in a 3-Dimension structure. Noting, all the standard textbooks of physics and engineering irrespective of the used components are circuits assembled in two dimensions. Here, by deviating from the “norm” we consider a case where the resistors are arranged in a 3D structure;e.g., a cube. Although, independent of the dimension of the design the same physics principles apply, transitioning from a 2D to a 3D makes the corresponding analysis considerably challenging. In general, with no exception, depending on the used components the analysis faces with solving a set of either algebraic or differential-algebraic equations. Practically, this interfaces with a Computer Algebra System (CAS). The main objective is symbolically to identify the current distributions and the equivalent resistor (s) of cubically assembled resistors.

Three Dimensional Electric Circuits with Multiple Capacitors and Resistors

Two cubical 3D electric circuits with single and double capacitors and twelve ohmic resistors are considered. The resistors are the sides of the cube. The circuit is fed with a single internal emf. The charge on the capacitor(s) and the current distributions of all twelve sides of the circuit(s) vs. time are evaluated. The analysis requires solving twelve differential-algebraic intertwined symbolic equations. This is accomplished by applying a Computer Algebra System (CAS), specifically Mathematica. The needed codes are included. For a set of values assigned to the elements, the numeric results are depicted.

Energy model based sensorless estimation method for operational temperature of braking resistor onboard metro vehicles

Purpose–This study aims to improve the availability of regenerative braking for urban metro vehicles by introducing a sensorless operational temperature estimation method for the braking resistor(BR)onboard the vehicle,which overcomes the vulnerability of having conventional temperature sensor.Design/methodology/approach–In this study,the energy model based sensorless estimation method is developed.By analyzing the structure and the convection dissipation process of the BR onboard the vehicle,the energy-based operational temperature model of the BR and its cooling domain is established.By adopting Newton’s law of cooling and the law of conservation of energy,the energy and temperature dynamic of the BR can be stated.To minimize the use of all kinds of sensors(including both thermal and electrical),a novel regenerative braking power calculation method is proposed,which involves only the voltage of DC traction network and the duty cycle of the chopping circuit;both of them are available for the traction control unit(TCU)of the vehicle.By utilizing a real-time iterative calculation and updating the parameter of the energy model,the operational temperature of the BR can be obtained and monitored in a sensorless manner.Findings–In this study,a sensorless estimation/monitoring method of the operational temperature of BR is proposed.The results show that it is possible to utilize the existing electrical sensors that is mandatory for the traction unit’s operation to estimate the operational temperature of BR,instead of adding dedicated thermal sensors.The results also validate the effectiveness of the proposal is acceptable for the engineering practical.Originality/value–The proposal of this study provides novel concepts for the sensorless operational temperature monitoring of BR onboard rolling stocks.The proposed method only involves quasi-global electrical variable and the internal control signal within the TCU.

旋转部件温度参数同步无线测量技术研究

针对旋转部件温度参数原位同步测量和数据无线传输应用需求,研究了电能无线传输技术和空间光通信技术,设计了一套8通道小型温度参数遥测系统。该系统通过热电偶和铂电阻传感器实现8路温度参数的高精度准确测量,采用电磁感应和红外光通信技术实现电能和采集数据的同步无线传输。系统分析软件完成数据的实时存储、解析和可视化显示。搭建了20000 r/min的模拟旋转环境测试平台,进行系统功能和性能验证。系统温度采集精度优于0.15%,无线传输距离为15 mm,电能传输输出峰值功率可达5 V/400 mA,实测通信速率为10 Mbit/s,8通道同步采样速率为56 kHz。该系统实现了温度参数的分布式、高精度获取,为旋转部件的研制和维护提供了准确的温度依据。

计及杂散参数的柔性直流启动电阻冲击电压分布特性研究

针对柔性直流输电系统中启动电阻异常放电问题。首先,从启动电阻温升、绝缘水平、电流应力及冲击能量几方面进行校核分析;然后,对现场启动电阻进行拆解,定量分析启动电阻放电原因;最后,利用Ansys搭建电阻器杂散电容求解模型,根据分布电容求解结果,基于PSCAD搭建电阻塔的宽频等效模型,仿真分析启动电阻在冲击电压下的电位分布规律,验证启动电阻异常放电机理并提出优化改进措施。研究结果可为今后柔性直流输电系统启动电阻的选型设计提供参考。

基于MMC的分布式储能系统及其快速SOC均衡控制策略

提高基于模块化多电平换流器(modular multilevel converter,MMC)的分布式储能系统(distributed energy storage systems,DESS)的能量利用率,解决储能子模块(energy sub-module,ESM)荷电状态(state of charge,SOC)均衡问题至关重要。针对现有的SOC均衡控制策略的不足,提出内外分层的快速SOC均衡控制策略。外层针对桥臂间或相间的SOC差异,通过改进MMC模型预测控制(model predictive predictive control,MPC),配合自适应均衡系数,快速调整功率差额。内层引入自适应虚拟电阻法,根据ESM的SOC情况确定主导ESM,自适应调节各单元的虚拟电阻,产生相应的电压梯度,结合MMC排序算法使ESM按照各自SOC进行功率分配,从而实现ESM的SOC快速均衡,提高DESS能量利用率。通过在Matlab/Simulink构建仿真模型,证明了所提控制策略的有效性和可行性。

一种新型可移动TEM喇叭辐射波模拟器的模拟优化

为改善基于TEM喇叭的辐射波模拟器的低频辐射特性从而展宽其辐射近场半高宽,首次提出了在指数型TEM喇叭上/下两个极板的端口加上2个金属直板、并通过倾斜金属板和并联电阻相连的新型可移动模拟器的设计方案。基于FDTD方法模拟分析了该新型模拟器的特性参数对其近场辐射性能的影响,并给出了优化后的模拟器及其阵列的辐射特性。计算结果表明:尺寸为6 m×6 m×6.24 m的优化后的新型模拟器在距离口面3 m的中心位置的辐射近场脉宽能达到18.95 ns,而达到相同低频辐射性能的常规模拟器尺寸为9 m×12 m×6.8 m。且与常规模拟器相比,优化后的模拟器的场峰值更大。与前人的研究相比,优化后的模拟器场在保持高峰值的同时,时域波形后延震荡的幅度与主峰的比值明显减小。优化后的模拟器2×2阵列模型的测试平面中心点场峰值最大,且在测试平面上满足6 dB均匀性要求的有效测试区最大;有效测试区在横向上范围最大的是2×2阵列模型,其次是2×1阵列模型;在纵向上范围最大的是2×2阵列模型及1×2阵列模型。

某电源模块厚膜电阻硫化机理及防护对策

针对本单位某型电子产品内主板的电源模块上的厚膜电阻首次出现硫化的问题,开展了行业现状调研,研究了厚膜电阻硫化机理,分析了电源模块上厚膜电阻硫化的原因。从器件选型、设计优化、工艺改进三个方面提出了提升电源模块抗硫化能力的防护措施。重点论述了涂覆三防漆的改善措施,且经工艺验证可行,能够起到提升电源模块防硫化能力的作用。

基于运放的受控源实现方法

探讨四种受控源模型的实现方法及其应用,并利用Multisim软件验证电路实现结果的正确性。首先利用运放同相放大器实现电压控制电压源,在此基础上给出了负电阻实现电路设计的一种解释方法。利用电压控制电压源和负电阻实现电路,通过电路的等效变换给出了其他三种受控源的实现电路。所讨论的方法为实现一般二端口电路提供了一种设计思路。

硅压阻式压力敏感芯体应变电阻失效分析

通过对硅压阻式压力敏感芯体内部应变电阻失效故障的排查及定位分析,确立了应变电阻缺陷造成传感器失效机理,总结激发应变电阻缺陷暴露的检测方法,确定对压力敏感芯体进行1200 h常温电老炼的筛选方案。筛选试验结果表明:增加1200 h常温电老炼后,可剔除由于应变电阻缺陷造成敏感芯体输出漂移的失效元件。

一种基于PIN二极管的可切换吸透一体超材料设计

设计并验证了一种基于集总电阻和PIN二极管的可切换吸透一体超材料结构,以实现宽带透波和通带可开关特性。该超材料单元结构由连接集总电阻的交指谐振器、带通频率选择表面层以及加载PIN二极管的开关控制层组成。通过等效电路理论对单元结构与谐振频率之间的关系进行了分析。通过对单元结构的表面电流和电场分布的分析,揭示了其吸波机理。研究结果表明:当PIN二极管处于导通状态时,设计的结构在9.48~10.31GHz透波频段内插入损耗低于1d B,在5.34~8.08GHz和11.89~15.14GHz频段内具有90%以上的吸波率,并且在5.21~15.37GHz频带内整体反射系数低于-10d B,展现出良好的宽频隐身效果;而当PIN二极管处于截止状态时,原本的通带变为全反射带,反射系数大于-1d B。这一设计在隐身领域具有潜在应用价值。

基于FSR嵌入的智能泡沫在气动夹爪的应用

如何控制工业夹爪对易损物体的夹持力是一件具有挑战的任务,通常是利用有着力传感器的电动夹爪进行反馈控制,但这种方法昂贵且额外增加了夹爪的复杂程度。基于直书写3D打印,设计了一种内嵌力敏电阻器(FSR)的智能硅橡胶泡沫,安装在气动夹爪的指尖,不仅能监测夹持状态,还能在气压超过阈值后一定范围内,保持夹持力的恒定,以保护物体。实验结果表明:智能泡沫在4~12 N的工作范围内,误差不超过1.5N。当气压在450~560kPa范围内,能维持夹持力约14.6N。

船舶无刷相复励同步发电机励磁系统设计

以船舶无刷相复励同步发电机为研究对象。首先,介绍了其工作原理与励磁特性,推导了相复励输出电流计算式;然后,针对发电机调节特性无法全补偿励磁装置输出特性的问题,设计了合适的励磁电流过补偿系数,通过与分流电阻独特的工作机制相配合来实现端口电压的稳定;其次,根据该设计方案给出了主要元件参数的计算方法,并建立仿真模型,在稳态和动态两种负载工况下进行仿真验证;最后,根据已有电机参数与所提设计方案制造了一台25 kVA试验样机,试验结果表明所设计的可控励磁系统能够通过控制分流电阻的通断调整励磁电流大小,随着负载的波动仍能实现端口电压的稳定。将计算和仿真结果与试验测量结果进行对比分析,计算误差小于1%,验证了推导计算式的有效性;仿真误差小于3.5%,表明模型能够较好地反映样机的稳态与动态特性,验证了过补偿设计方案的合理性。

超宽带薄型频率选择表面吸波体设计

设计了一种新型集总电阻加载超宽带薄型频率选择表面(FSS)吸波体。该吸波体使用单层单谐振FSS损耗层结构,具有厚度薄、宽带吸波且极化稳定的特点。FSS损耗层单元结构采用非单元中心对称轴集总电阻加载方法,并结合非均匀金属导带宽度和圆顶枝节加载设计有效拓宽了吸波带宽。该吸波体的等效电路分析及全波仿真结果均表明该结构在6.0~26.77 GHz频段内对电磁波吸波率能够达到90%,相对带宽达到126.8%。该吸波体总厚度为0.086λ_(L)(λ_(L)为吸波频段最低频率对应波长),仅为Rozanov理论极限厚度的1.09倍。对该吸波体进行加工与测试,实测结果与仿真结果一致,验证了设计的有效性。

曲面电路中喷墨打印薄层电阻的可靠性

针对曲面电路中无法采用片式贴片电阻回流焊接的难题,创新地采用喷墨打印技术打印曲面薄层电阻,开展了高温环境对薄层电阻阻值变化的影响研究。经测试,喷墨打印曲面电路中薄层电阻在经过高温可靠性测试后,薄层电阻结合力和阻值变化均能达到设计要求,电阻阻值精度为±20%。论证了曲面电路中喷墨打印薄层电阻的可靠性,可有效用于射频曲面电路的快速制造和快速验证,并缩短了研发周期。

基于石英薄膜工艺的D波段固定衰减器设计及实现

薄膜电阻具有较为精确的电阻值,可用于微波固定衰减器设计。然而随着工作频率的升高,薄膜电阻的寄生参数随之增大,影响固定衰减器的衰减精度及回波性能。本文基于传统微波频段薄膜电阻等效电路模型,提出了一种十四元件等效电路模型。采用Ansys HFSS软件对薄膜电阻进行三维电磁场仿真并提取其S参数,通过S参数曲线拟合,最终确定各元件参数值。仿真结果表明,该等效电路模型在0.1~180.0 GHz可有效表征薄膜电阻的电气特性。在此基础上,采用石英薄膜工艺研制了三款不同衰减值的D波段(110~170 GHz)固定衰减器,并通过在片匹配电路补偿键合金丝和薄膜电阻寄生参量的影响。此外,还设计了波导-微带转换电路,将微带模式转换为标准波导模式进行衰减器性能的测量。测试结果表明,在110~170 GHz频带内,3 dB衰减器的衰减典型值为4 dB,回波损耗大于13.3 dB;6 dB衰减器的衰减典型值为5.5 dB,回波损耗大于11.4 dB;9 dB衰减器的衰减典型值为8 dB,回波损耗大于11.4 dB。研制的固定衰减器可将现有固定衰减器的工作频率拓宽至110 GHz以上,用于信号功率调节及改善器件级间回波的影响。