Single-phase-to-ground fault protection based on zero-sequence current ratio coefficient for low-resistance grounding distribution network

Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to their high settings of the action value when a high-impedance grounding fault occurs.In this study,the relationship between the zero-sequence currents of each feeder and the neutral branch was analyzed.Then,a grounding protection method was proposed on the basis of the zero-sequence current ratio coefficient.It is defined as the ratio of the zero-sequence current of the feeder to that of the neutral branch.Nonetheless,both zero-sequence voltage and zero-sequence current are affected by the transition resistance,The influence of transition resistance can be eliminated by calculating this coefficient.Therefore,a method based on the zero-sequence current ratio coefficient was proposed considering the significant difference between the faulty feeder and healthy feeder.Furthermore,unbalanced current can be prevented by setting the starting current.PSCAD simulation results reveal that the proposed method shows high reliability and sensitivity when a high-resistance grounding fault occurs.

High-Performance In0.23Ga0.77As Channel MOSFETs with High Current Ratio Ion/Ioff Grown on Semi-insulating GaAs Substrates by MOCVD

We demonstrate high-performance In0.23 Ga0.77 As channel metal-oxide-semiconductor field-effect transistors （ MOS- FETs） with high on-current to off-current （Ion/Ioff） ratio grown on semi-insulating GaAs wafers by metal-organic chemical vapor deposition （MOCVD）. The 2μm channel-length devices exhibit a peak extrinsic transeonductance of 150 mS/mm and a drain current up to 500 mA/mm. The maximum effective mobility is 1680 cm2/Vs extracted by the split C-V method. Furthermore, the Ion/Ioff ratio is significantly improved from approximately 4.5 × 10^3 up to approximately 4.32 × 10^4 by controlling the etch thickness of In0.49Ga0.51P, The high drain current and high Ion/Ioff ratio of the In0.23Ga0.77As channel MOSFETs are achieved due to the high effective mobility and the low gate leakage current density.

Location of Asymmetric Ground Fault Using Virtual Injected Current Ratio and Two-stage Recovery Strategy in Distribution Networks

Sparse measurements challenge fault location in distribution networks.This paper proposes a method for asymmetric ground fault location in distribution networks with limited measurements.A virtual injected current vector is formulated to estimate the fault line,which can be reconstructed from voltage sags measured at a few buses using compressive sensing(CS).The relationship between the virtual injected current ratio(VICR)and fault position is deduced from circuit analysis to pinpoint the fault.Furthermore,a two-stage recovery strategy is proposed for improving reconstruction accuracy of the current vector,where two different sensing matrixes are utilized to improve the incoherence.The proposed method is validated in IEEE 34 node test feeder.Simulation results show asymmetric ground fault type,resistance,fault position and access of distributed generators(DGs)do not significantly influence performance of our method.In addition,it works effectively under various scenarios of noisy measurement and line parameter error.Validations on 134 node test feeders prove the proposed method is also suitable for systems with more complex structure.

Flexible UV detectors based on in-situ hydrogen doped amorphous Ga_(2)O_(3) with high photo-to-dark current ratio

Amorphous Ga_(2)O_(3)(a-Ga_(2)O_(3))has been attracting more and more attention due to its unique merits such as wide bandgap(∼4.9 eV),low growth temperature,large-scale uniformity,low cost and energy efficient,making it a powerful competitor in flexible deep ultraviolet(UV)photodetection.Although the responsivity of the ever-reported a-Ga_(2)O_(3)UV photodetectors(PDs)is usually in the level of hundreds of A/W,it is often accompanied by a large dark current due to the presence of abundant oxygen vacancy(VO)defects,which severely limits the possibility to detect weak signals and achieve versatile applications.In this work,the VO defects in a-Ga_(2)O_(3)thin films are successfully passivated by in-situ hydrogen doping during the magnetron sputtering process.As a result,the dark current of a-Ga_(2)O_(3)UV PD is remarkably suppressed to 5.17×10^(-11) A at a bias of 5 V.Importantly,the photocurrent of the corresponding device is still as high as 1.37×10^(-3)A,leading to a high photo-to-dark current ratio of 2.65×107 and the capability to detect the UV light with the intensity below 10 nW cm^(-2).Moreover,the H-doped a-Ga_(2)O_(3)thin films have also been deposited on polyethylene naphtholate substrates to construct flexible UV PDs,which exhibit no great degradation in bending states and fatigue tests.These results demonstrate that hydrogen doping can effectively improve the performance of a-Ga_(2)O_(3)UV PDs,further promoting its practical application in various areas.

High peak-to-valley current ratio In_(0.53)Ga_(0.47)As/AlAs resonant tunneling diode with a high doping emitter

An In0.53Ga0.47As/AlAs resonant tunneling diode （RTD） with a high doping emitter is designed and fabricated using air bridge technology. The RTD exhibits a high peak-to-valley current ratio （PVCR） of more than 40 at room temperature, with a peak current density of 24 kA/cm2. The extraction of device parameters from DC and microwave measurements is presented together with an RTD equivalent circuit. The high PVCR RTD with small intrinsic capacitance is favorable for microwave/THz applications.

Relationship between the Current Account Balance Ratio and Salary Ratio in Japanese Municipal Hospitals

Background: While public municipal hospitals in Japan are supported by public financing and are less likely to fail than private hospitals, more than half are in financial deficit. Hospitals running at a deficit may have poorer outcomes and less investment in maintenance of human or physical capital, as well as increased rates of patient adverse events. We sought to clarify the relationship between municipal hospital surpluses or deficits and salary expenditures. Methods: We extracted financial data for 253 general hospitals of 300 beds or more from financial statements for the 2013 fiscal year available in the Yearbook of Public Firms, Edition for Hospital. From these data, we calculated account balance ratios and compared the average value of the ratio of labor to the output (salary ratio) for each group using analysis of variance (ANOVA). Results: The salary ratios of hospitals in the surplus group were significantly lower than the salary ratios of hospitals in the deficit group (55.5% vs. 49.4%;p p = 0.342). In the surplus group, the average value of salary ratios was different among the three-bed count groups (mean salary ratio: 53.0% vs. 48.5% vs. 47.4%;ANOVA p = 0.012). In addition, there was a significant difference in mean value between the 300-bed group and ≥500 beds group (mean salary ratio: 53.0% vs. 47.4%;p = 0.002). Conclusion: This study suggests that maintaining a favorable salary ratio to the current account balance is a useful proxy of fiscal health, and interventions to improve the salary ratio may be effective in improving municipal hospital management. Furthermore, among well-managed municipal hospitals, larger hospital size may confer some advantage in purchasing power.

Effect of Distortion Ratio on Local Scour Under Tidal Currents and Waves

Five generalized physical models of different distortion ratios were built according to DOU Guo-ren's similarity theory of total sediment transport modeling for estuarine and coastal regions. Experiments on local scour in front of groins were made under the actions of tidal currents and waves with clear and sediment entraining water. The scour depths under different dynamic actions are compared. The effect of the distortion ratio on the depth of scour hole is discussed. A relationship between scour depths for distorted and undistorted models is given.

一种优化开关磁阻电机换相区控制策略的高效率转矩分配函数

转矩分配函数被广泛应用于抑制开关磁阻电机的转矩脉动。然而,输入相转矩跟踪不足或者输出相产生较大的负转矩这两种情况通常会导致电机的转矩脉动难以得到有效抑制,并降低电机的运行效率。因此,为了能够有效降低电机的转矩脉动并提高电机的效率,提出了一种新型的转矩分配函数控制策略。在提出的转矩分配函数控制策略中,电机的换相区域分为两个区域。在前一区域中,通过降低输入相转矩分配的比例,可以实现输入相实际转矩快速跟踪参考转矩,电机的转矩脉动有效降低。同时由于在输入相电感变化率较低时减少输入相分配的转矩,从而输入相的峰值电流随之降低,电机的转矩电流比提高。在后一区域中,将输出相的电流在转子对齐位置附近处减小到0,以避免产生较大的负转矩。因此,在所提出的方案下,电机的转矩脉动得到有效抑制,电机的效率也得到了提高。为了验证该方法的有效性,在一台12/8三相开关磁阻电机上进行了仿真和实验。结果表明,所提出的转矩分配函数控制策略能有效降低开关磁阻电机转矩脉动,也能有效地提高开关磁阻电机的运行效率。

10 × 10 Ga_(2)O_(3)-based solar-blind UV detector array and imaging characteristic

A 10 × 10 solar-blind ultraviolet(UV) imaging array with double-layer wire structure was prepared based on Ga_(2)O_(3) film grown by atomic layer deposition. These single detection units in the array exhibit excellent performance at 3 V: photo-todark current ratio(PDCR) of 5.5 × 10^(5), responsivity(R) of 4.28 A/W, external quantum efficiency(EQE) of 2.1 × 10^(3)%, detectivity(D*) of 1.5 × 10^(14) Jones, and fast response time. The photodetector array shows high uniformity under different light intensity and low operating bias. The array also has good temperature stability. Under 300 ℃, it still presents clear imaging and keeps high R of 34.4 and 6.45 A/W at 5 and 1 V, respectively. This work provides a new insight for the large-scale array of Ga_(2)O_(3) solarblind UV detectors.

基于联合仿真的电励磁同步电机线性自抗扰控制

针对电励磁同步电机(EESM)在车用电机控制方向的研究,通过Maxwell设计EESM有限元模型,基于Simulink搭建电机控制系统模型。然后,根据凸极EESM的电机特性和电磁转矩分析,在控制系统中采用最大转矩电流比(MTPA)矢量控制方式在Simulink-Maxwell进行EESM控制系统的联合仿真验证。同时,控制系统电流环应用线性自抗扰控制(LADRC),基于电机已知参数在LADRC中设计模型辅助—扩张状态观测器(MA-LESO),以观测和消除系统扰动变量。仿真实验表明,采用MTPA矢量控制的电机在带载时转速波动降低,带载能力增强;在电流环中采用MA-LESO的LADRC控制器能使电机转速在稳态时波动更小,在带载时的抗干扰性能更强,电机运行过程相对稳定;电机负载转矩和定子电流在空载、负载时的波形更稳定,显著提升了电机运行性能。

多孔n-GaN/p-Zn_(x)Cu_(1-x)S异质结的制备及紫外探测性能研究

本文首先采用紫外光辅助电化学刻蚀(UV-EC)方法制备出了孔隙密度为1.51×10^(10)cm^(-2)、平均孔径为38 nm的多孔n-GaN薄膜;随后在其上通过水浴法沉积了一系列Zn_(x)Cu_(1-x)S复合薄膜,x为0.0、0.2、0.4、0.6、0.8、1.0,形成的多孔n-GaN/p-Zn_(x)Cu_(1-x)S异质结带隙在2.34~3.51 eV调控;最后基于这些异质结构建出p-n结型紫外探测器。I-V曲线结果表明这些探测器均具有良好的整流特性,特别是n-GaN/p-Zn_(0.4)Cu_(0.6)S探测器性能最优。在暗态下,I_(+3 V)/I_(-3 V)约为1.78×10~5;在偏压为-3 V、光功率密度为432μW/cm^(2)(365 nm)的条件下,光暗电流比超过10~3,上升/下降时间为0.09/39.8 ms,响应度(R)为0.352 A/W,外量子效率(EQE)为119.6%,探测率(D^(*))为3.21×10^(12)Jones。I-t曲线结果表明,多孔n-GaN/p-Zn_(x)Cu_(1-x)S异质结紫外探测器在连续开-关光循环过程中拥有稳定的光电流响应。该研究为制备异质结紫外探测器提供了一定的理论指导和实验数据。

Saturation Ion Current Densities in Inductively Coupled Hydrogen Plasma Produced by Large-Power Radio Frequency Generator

An experimental investigation of the saturation ion current densities （Jions） in hydrogen inductively coupled plasma （ICP） produced by a large-power （2-32 kW） radio frequency （RF） generator is reported, then some reasonable explanations are given out. With the increase of RF power, the experimental results show three stages： in the first stage （2-14 kW）, the electron temperature will rise with the increase of RF power in the ICP, thus, the Jions increases continually as the electron temperature rises in the ICP. In the second stage （14 20 kW）, as some H- ions lead to the mutual neutralization （MN）, the slope of Jio^s variation firstly decreases then increases. In the third stage （20-32 kW）, both the electronic detachment （ED） and the associative detachment （AD） in the ICP result in the destruction of H- ions, therefore, the increased amplitude of the Jions in the third stage is weaker than the one in the first stage. In addition, with the equivalent transformer model, we successfully Explain that the Jions at different radial locations in ICP has the same rule. Finally, it is found that the Jions has nothing to do with the outer/inner puffing gas pressure ratio, which is attributed to the high-speed movement of hydrogen molecules.

基于工程应用的CW-GMAW熔滴过渡形态表征

综述了涉及工程应用的冷丝熔化极气体保护焊(Cold wire gas metal arc welding,CW-GMAW)熔滴过渡形态特征。结果表明,在大电流、强规范、富氩混合气体保护下,CW-GMAW工艺的熔滴过渡形态呈喷射过渡;当电流较小、电弧电压较低时,可能为滴状过渡,甚至在弧压很低时,呈现短路过渡形态。该工艺电弧发生偏向冷丝的位移,弧长变短甚至发生短路,与冷丝送进速率比增高及冷丝在电弧中产生大量金属蒸气时弧柱电阻下降有关。在具有富氩混合保护气体的相同工艺参数下,CWGMAW转变电流比GMAW降低了4%~7%。焊接工艺参数对CW-GMAW和GMAW工艺熔滴过渡形态的影响规律大致相近,但前者因涉及冷丝送进速率比和电极焊丝送进速度,以及它们的匹配等,使焊接电流的影响更为复杂。

在等电位工作状态下校准多元感应分流器

提出了在等电位工作状态下校准多元感应分流器(multiple inductive current divider,MICD)的1种方法。在校准装置中加入由跟随器和电阻组成的I/V变换器,以使MICD各支路间的电流比例与其工作状态保持一致;用参考电流互感器(CT)提供独立的参考电流,以避免影响支路电流的比例关系。在20、55、400 Hz及1 kHz下对11支路MICD校准所得10:1电流比例的比值差合成标准不确定度优于0.2μA/A,相位差合成标准不确定度优于1.5μrad。

矿渣水泥基复合材料在杂散电流作用下的抗软水溶蚀机理研究

在轨道交通工程运营期间,复杂的服役环境导致混凝土结构耐久性下降。本文主要研究了在杂散电流与软水溶蚀耦合作用下,矿渣掺量、水胶比和杂散电流电压强度对矿渣水泥基复合材料微观结构的影响。结合X射线衍射、热重、扫描电子显微镜和压汞等方法,分析了矿渣水泥基复合材料经溶蚀90 d后的物相组成、Ca(OH)_(2)含量、微观形貌以及孔结构变化。研究结果表明:矿渣掺量越大,矿渣水泥基复合材料内部的Ca(OH)_(2)含量越少,材料的孔隙率越低,结构更均匀致密;随着杂散电流电压强度的增加,矿渣水泥基复合材料内部的Ca(OH)_(2)和AFt含量变少,且AFt和Ca(OH)_(2)等物相边界变得模糊不清;矿渣水泥基复合材料中C-(A)-S-H的含量略有增多,孔隙率略有下降;随着水胶比的增大,矿渣水泥基复合材料内部的Ca(OH)_(2)含量变少,剩余物相含量变少,微观结构变得松散多孔,孔径结构整体粗化,孔隙率增大。

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。

Experimental Study on Wire Melting Control Ability of Twin-Body Plasma Arc

The twin-body plasma arc has the decoupling control ability of heat transfer and mass transfer,which is beneficial to shape and property control in wire arc additive manufacturing.In this paper,with the wire feeding speed as a characteristic quantity,the wire melting control ability of twin-body plasma arc was studied by adjusting the current separation ratio(under the condition of a constant total current),the wire current/main current and the position of the wire in the arc axial direction.The results showed that under the premise that the total current remains unchanged(100 A),as the current separation ratio increased,the middle and minimum melting amounts increased approximately synchronously under the effect of anode effect power,the first melting mass range remained constant;the maximum melting amount increased twice as fast as the middle melting amount under the effect of the wire feeding speed,and the second melting mass range was expanded.When the wire current increased,the anode effect power and the plasma arc power were both factors causing the increase in the wire melting amount;however,when the main current increased,the plasma arc power was the only factor causing the increase in the wire melting amount.The average wire melting increment caused by the anode effect power was approximately 2.7 times that caused by the plasma arc power.The minimum melting amount was not affected by the wire-torch distance under any current separation ratio tested.When the current separation ratio increased and reached a threshold,the middle melting amount remained constant with increasing wire-torch distance.When the current separation ratio continued to increase and reached the next threshold,the maximum melting amount remained constant with the increasing wire-torch distance.The effect of the wire-torch distance on the wire melting amount reduced with the increase in the current separation ratio.Through this study,the decoupling mechanism and ability of this innovative arc heat source is more clearly.

Electrodeposition of Gold to Conformally Fill High-Aspect-Ratio Nanometric Silicon Grating Trenches: A Comparison of Pulsed and Direct Current Protocols

Filling high-aspect-ratio trenches with gold is a frequent requirement in the fabrication of X-ray optics as well as micro-electronic components and other fabrication processes. Conformal electrodeposition of gold in sub-micron-width silicon trenches with an aspect ratio greater than 35 over a grating area of several square centimeters is challenging and has not been described in the literature previously. A comparison of pulsed plating and constant current plating led to a gold electroplating protocol that reliably filled trenches for such structures.

采用MPC-MTPA的新能源车永磁同步电机控制研究

针对传统永磁同步电机控制器结构复杂,负载突变时动态响应速度慢,导致电机抗干扰能力差、工作效率低的问题,提出了一种模型预测控制(model predictive control,MPC)融合最大转矩比控制(maximum torque per ampere,MTPA)的电机非级联控制方法。构建MPC和MTPA控制器,利用MPC中的代价函数同时完成转矩控制和MTPA控制,在代价函数中引入动态分配的权重系数优化非级联MPC-MTPA控制器。仿真和试验结果表明:相比传统电机控制方法,提出的变权重系数非级联MPC-MTPA控制方法的稳定性提高约26%,动态响应特性提高约50%。

基于槽极比选择的切向永磁同步电机永磁体涡流损耗抑制措施

为抑制切向永磁同步电机的永磁体涡流损耗,基于麦克斯韦方程和本构方程,对永磁体形状进行近似假设,构建了永磁体涡流损耗的估算模型。使用一种基于卡特系数概念的磁导函数来估算由于定子开槽引起的槽下磁感应强度变化。基于五台槽极比分别为1.05、1.20、1.30、2.40和3.60的电机设计方案对理论分析结论进行了验证。在负载电流和两倍负载电流下,分析永磁体损耗,得到了每台电机的径向气隙磁密曲线及其谐波含量。考虑到增加槽极比对定子铁耗和永磁体涡流损耗的削弱效果,给出了电机槽极比选择策略。研究结果表明,增加槽极比能减弱定子槽下磁感应强度变化,从而抑制气隙磁场中低次谐波含量,减小永磁体涡流损耗,使电机运行更加可靠,但也会引入更多高次谐波,从而增加定子铁耗。