Application of fractal theory in detecting low current faults of power distribution system in coal mines

Single-phase low current grounding faults areoften seen in power distribution system of coal mines.These faults are difficult to reliably identify.We propose a new method of single-phase ground fault protection based upon a discernible matrix of the fractal dimension associated with line currents.The method builds on existing selective protection methods.Faulted feeders are distinguished using differences in the zero-sequence transient current fractal dimension.The current signals were first processed through a fast Fourier transform and then the characteristics of a faulted line were identified using a discernible matrix.The method of calculation is illustrated.The results show that the method involves simple calculations, is easy to do and is highly accurate.It is, therefore, suitable for distribution networks having different neutral grounding modes.

Numerical Simulation of Low Current Vacuum Arc Supersonic Flow

Based on a two-dimensional axisymmetric magneto-hydrodynamic （MHD） model, low current vacuum arc （LCVA） characteristics are studied. The influence of cathode process under different axial magnetic fields and different anode radii on LCVA characteristics is also simulated. The results show that the influence of both cathode process and anode radii on LCVA is significant. The sign of anode sheath potentials can change from negative to positive with the decrease of anode radii. The simulation results are in part verified by experimental results. Especially, as the effect of ion kinetic energy is considered, ion temperature is improved significantly; which is in agreement with experimental results.

Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

In this study, the influence of the initial jet angles （IJAs） and ion number densities （INDs） at the cathode side on the low current vacuum arc （LCVA） characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.

Organic X-Ray Image Sensors Using a Medium Bandgap Polymer Donor with Low Dark Current

The development of portable X-ray detectors is necessary for diagnosing fractures in unconscious patients in emergency situations.However,this is quite challenging because of the heavy weight of the scintillator and silicon photodetectors.The weight and thickness of X-ray detectors can be reduced by replacing the silicon layer with an organic photodetectors.This study presents a novel bithienopyrroledione-based polymer donor that exhibits excellent photodetection properties even in a thick photoactive layer(~700 nm),owing to the symmetric backbone and highly soluble molecular structure of bithienopyrroledione.The ability of bithienopyrroledione-based polymer donor to strongly suppress the dark current density(Jd~10−10 A cm^(−2))at a negative bias(−2.0 V)while maintaining high responsivity(R=0.29 A W−1)even at a thickness of 700 nm results in a maximum shot-noise-limited specific detectivity of D_(sh)^(*)=2.18×10^(13)Jones in the organic photodetectors.Printed organic photodetectors are developed by slot-die coating for use in X-ray detectors,which exhibit D_(sh)^(*)=2.73×10^(12)Jones with clear rising(0.26 s)and falling(0.29 s)response times upon X-ray irradiation.Detection reliability is also proven by linear response of the X-ray detector,and the X-ray detection limit is 3 mA.

An NMOS output-capacitorless low-dropout regulator with dynamic-strength event-driven charge pump

In this paper,an NMOS output-capacitorless low-dropout regulator(OCL-LDO)featuring dual-loop regulation has been proposed,achieving fast transient response with low power consumption.An event-driven charge pump(CP)loop with the dynamic strength control(DSC),is proposed in this paper,which overcomes trade-offs inherent in conventional structures.The presented design addresses and resolves the large signal stability issue,which has been previously overlooked in the event-driven charge pump structure.This breakthrough allows for the full exploitation of the charge-pump structure's poten-tial,particularly in enhancing transient recovery.Moreover,a dynamic error amplifier is utilized to attain precise regulation of the steady-state output voltage,leading to favorable static characteristics.A prototype chip has been fabricated in 65 nm CMOS technology.The measurement results show that the proposed OCL-LDO achieves a 410 nA low quiescent current(IQ)and can recover within 30 ns under 200 mA/10 ns loading change.

A novel electrical measurement method of peak junction temperature based on the excessive thermotaxis effect of low current

It has been a scientific and technological problem in the field of microelectronics for several decades that the electrical method is used to measure the peak junction temperature of power transistors. Based on the excessive thermotaxis effect of low current, a novel electrical measurement method of the peak junction temperature is presented in this paper. The method is called the thermal spectrum analysis method of transistors, simply designated TSA （thermal spectrum analysis method）. Unlike the common method which uses a single measuring current, TSA uses multi-step currents to measure temperature-sensitive parameters. Based on the excessive thermotaxis effect of low current and the sub-transistor parallel model, the peak junction temperature and non-uniform property of junction temperature distribution are analyzed successfully.

Single-mode low threshold current multi-hole vertical-cavity surface-emitting lasers

A multi-hole vertical-cavity surface-emitting laser （VCSEL） operating in stable single mode with a low threshold current was produced by introducing multi-leaf scallop holes on the top distributed Bragg-refleetor of an oxidation- confined 850 nm VCSEL. The single-mode output power of 2.6 mW, threshold current of 0.6 mA, full width of half maximum lasing spectrum of less than 0.1 nm, side mode suppression ratio of 28.4 dB, and far-field divergence angle of about 10% are obtained. The effects of different hole depths on the optical characteristics are simulated and analysed, including far-field divergence, spectrum and lateral cavity mode. The single-mode performance of this multi-hole device is attributed to the large radiation loss from the inter hole spacing and the scattering loss at the bottom of the holes, particularly for higher order modes.

An Ultra-Low Quiescent Current CMOS Low-Dropout Regulator with Small Output Voltage Variations

An ultra-low quiescent current low-dropout regulator with small output voltage variations and improved load regulation is presented in this paper. It makes use of dynamically-biased shunt feedback as the buffer stage and the LDO regulator can be stable for all load conditions. The proposed structure also employs a momentarily current-boosting circuit to reduce the output voltage to the normal value when output is switched from full load to no load. The whole circuit is designed in a 0.18 μm CMOS technology with a quiescent current of 550 nA. The maximum output voltage variation is less than 20 mV when used with 1 μF external capacitor.

Low-leakage-current AlGaN/GaN HEMTs on Si substrates with partially Mg-doped GaN buffer layer by metal organic chemical vapor deposition

High-performance low-leakage-current A1GaN/GaN high electron mobility transistors （HEMTs） on silicon （111） sub- strates grown by metal organic chemical vapor deposition （MOCVD） with a novel partially Magnesium （Mg）-doped GaN buffer scheme have been fabricated successfully. The growth and DC results were compared between Mg-doped GaN buffer layer and a unintentionally onμe. A 1μ m gate-length transistor with Mg-doped buffer layer exhibited an OFF-state drain leakage current of 8.3 × 10-8 A/mm, to our best knowledge, which is the lowest value reported for MOCVD-grown A1GaN/GaN HEMTs on Si featuring the same dimension and structure. The RF characteristics of 0.25-μ m gate length T-shaped gate HEMTs were also investigated.

Impact of the South China Sea Throughflow on the Pacific Low-Latitude Western Boundary Current:A Numerical Study for Seasonal and Interannual Time Scales

Prior studies have revealed that,as a part of the Pacific tropical gyre,the South China Sea throughflow（SCSTF） is strongly influenced by the Pacific low-latitude western boundary current（LLWBC）.In this study,ocean general circulation model（OGCM） experiments with and without connection to the South China Sea（SCS） were performed to investigate the impact of the SCSTF on the Pacific LLWBC.These model experiments show that if the SCS is blocked,seasonal variability of the Kuroshio and Mindanao Current becomes stronger,and the meridional migration of the North Equatorial Current（NEC） bifurcation latitude is enhanced.Both in seasonal and interannual time scales,stronger Luzon Strait transport（LST） induces a stronger Kuroshio transport combined with a southward shift of the NEC bifurcation,which is unfavorable for a further increase of the LST;a weaker LST induces a weaker Kuroshio transport and a northward shifting NEC bifurcation,which is also unfavorable for the continuous decrease of the LST.

A Novel Ultra Low Power High Performance Atto-Ampere CMOS Current Mirror with Enhanced Bandwidth

A novel CMOS atto-ampere current mirror （AACM） is proposed which reaches the minimum yet reported current range of 0.4 aA. Operation of this circuit is based on the source voltage modulation instead of the conventionally used gate voltage modulation which interestingly prevents usage of commonly required voltage shifting in those circuits. The proposed circuit has a simple structure prohibiting large chip area consumption which consumes extremely low power of 1.5 μW. It is thus the best choice for ultra low power low voltage （ULPLV） applications. By using a very simple frequency compensation technique, its bandwidth is widened to 15.8 kHz. Simulation results in SMIC （Semiconductor Manufacturing International Corporation） 0.18 μm CMOS technology with Hspice are presented to demonstrate the validation of the proposed current mirror.

Development of Surface Grating Distributed Feedback Quantum Cascade Laser for High Output Power and Low Threshold Current Density

We report on the room-temperature cascade laser （QCL） at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback （DFB） quantum optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4- mm-long laser, high wall-plug efficiency of 6% is obtained at 20℃ from a single facet producing over I W of ew output power. The threshold current density of DFB QCL is as low as 1.13kA/cm^2 at 10℃ and 1.34kA/cm2 at 30℃ in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in tile working temperature range of 20-50℃.

DIRECT SOLUTION BY 2-D AND 3-D FINITE ELEMENT METHOD ON FORWARD PROBLEM OF LOW FREQUENCY CURRENT FIELDS IN INHOMOGENEOUS MEDIA

The paper adopts finite element method to analyze the forward problem of low-frequency current fields in inhomogeneous media. Firstly, the direct solution of 2-D and 3-D scalar potential is given. Secondly, the technique of covering finite elements for problems with movement has been presented; namely, when the place of testing point moved, the meshing data will be produced automatically to avoid re-meshing and distortion of the mesh. Thirdly the free and prescribed potential method is used to make the finite element coefficient matrices. Then this paper provides the result of a validity test obtained by simulating the laterolog-3 logging, compared with the numerical model-matching method. Finally, the MLL response is calculated.

Temperature-Dependent Drain Current Characteristics and Low Frequency Noises in Indium Zinc Oxide Thin Fihn Transistors

The I-V characteristics and low frequency noises for indium zinc oxide thin film transistor are measured between 250 K and 430 K. The experimental results show that drain currents are thermally activated following the Meyer Neldel rule, which can be explained by the multiple-trapping process. Moreover, the field effect electron mobility firstly increases, and then decreases with the increase of temperature, while the threshold voltage decreases with increasing the temperature. The activation energy and the density of localized gap states are extracted. A noticeable increase in the density of localized states is observed at the higher temperatures.

MODEL AND MODELING OF LOW TEMPERATURE CURRENT GAIN OF POLYSILICON EMITTER BIPOLAR TRANSISTORS

A unified model of low temperature current gain of polysilicon emitter bipolar transistors based on effective recombination method is presented, incorporating band-gap narrowing, carrier freezing-out, tunneling of holes through polysilicon/silicon interface oxide layer and reduced mobility mechanism in polysilicon. The modeling results based on this model are in good agreement with experimental data.

Reactive Current Allocation and Control Strategies Improvement of Low Voltage Ride Though for Doubly Fed Induction Wind Turbine Generation System

为满足风电机组低电压穿越（low voltage ride through,LVRT）的测试要求及其电气模型一致性评估需要,提出考虑向电网注入无功电流的双馈风电机组LVRT的控制策略。在阐述风电机组LVRT测试要求及控制原理的基础上,推导双馈发电机（doubly fed induction generator,DFIG）定子侧及网侧变流器输出无功电流极限表达式,研究电网电压跌落深度和发电机总输出有功功率对其无功电流极限值的影响规律,进而提出DFIG在LVRT期间的无功电流分配算法和改进的有功、无功功率控制策略。最后,以某实际2 MW双馈风电机组为例,分别对风速为5和12 m/s、电网电压对称跌落至20%和50%工况下的LVRT运行性能进行仿真比较和样机测试。与传统LVRT控制方法的对比表明,所提改进控制策略能更好地满足风电机组LVRT的测试要求。样机测试结果进一步证明了改进控制策略和仿真模型的有效性。

Current Efficiency of Low Temperature Aluminum Electrolysis Studied by Neural Network

A prediction model for Current Efficiency (CE) of low temperature aluminum electrolysis (LTAE) with the low molar ratioelectfolyte of Na3AIF6-AIF3 - CaF2-MgF2-LiF -Al2O3 system was investigated based on artificial neural network principles. The nonlinearmapping between CE of LATE and various electrolytic conditions was obtained from a number of experimental data and used to predictCE of LATE. The trsined neural networks possessed high precision and resulted in a good predicting effect. As a result, attificial neuralnetworks as a new cooperating and predicting technology provide a new approach to the further studies on low temperature aluminumelectrolysis.

A New Current Conveyor Full-Wave Rectifier for Low Frequency/Small Signal Medical Applications

This paper presents a new current conveyor (CCII+) full-wave rectifier for low frequency/small signal medical applications. The proposed rectifier is based on the current conveyor full-wave rectifier proposed previously, but the proposed rectifier is better in view of no need diodes to rectify, and no need bias sources to overcome the zero crossing error. It needs only two CCII+s, two resistors, and three simple current mirrors, which is easy for IC implementation and for building in many countries. The PSPICE simulation with the current conveyor CCII+ in the current feedback opamp AD844 IC and the 2N2222 bipolar current mirror shows the good low frequency/small signal rectification, the operation voltage of down to 6 .

低频电压下含纤维素颗粒变压器油绝缘特性及影响因素

低频变压器是低频输电系统中的关键设备,低频电压下的绝缘特性对其设计及运行具有重要意义。该文为了研究低频电压下含纤维素颗粒的变压器油的绝缘特性,分别研究20、30、40、50 Hz四种频率交流电压下不同纤维素颗粒度(低、中、高)水平的变压器油击穿特性。同时,通过仿真及试验分析不同频率下变压器油中纤维素颗粒运动及积聚过程。研究结果表明,交流电压频率对变压器油中纤维素颗粒的成桥特性及击穿电压具有显著影响。随着频率的降低,纤维素颗粒向电极移动速度变慢并难以黏附在电极表面,减缓了纤维素颗粒在电极表面的积聚过程及杂质小桥的形成速度。相同频率交流电压下,变压器油击穿电压均随颗粒物浓度的升高而降低;相同纤维素颗粒浓度下,变压器油击穿电压随着频率的降低而增大。研究结果为低频变压器的设计及运行维护提供了基础数据支撑。

DESIGN OF LOW-VOLTAGE AND LOW-POWER FULLY INTEGRATED FILTER BASED ON LOG-DOMAIN CURRENT-MODE INTEGRATOR

In this paper a novel log-domain current-mode integrator based on MOS transistors in subthreshold is proposed. The integrator's time-constant is tunable by varying a reference bias current. By use of the integrator, a fifth-order Chebyshev lowpass filter with 0.1dB ripples is designed. The simulation results demonstrate that the proposed filter has such advantages as low power supply(1.5V), very low power dissipation (μW level), nearly ideal frequency response, very small sensitivity to components in passband, and adjustable cut-off frequency over a wide range.The circuit is composed of NMOS transistors and grounded capacitors which make it suitable for fully integrated circuit implementation.