Light-extraction efficiency and forward voltage in GaN-based light-emitting diodes with different patterns of V-shaped pits

We present a new method of making a textured V-pit surface for improving the light extraction efficiency in GaN- based light-emitting diodes and compare it with the usual low-temperature method for p-GaN V-pits. Three types of GaNbased light-emitting diodes （LEDs） with surface V-pits in different densities and regions were grown by metal-organic chemical vapor deposition. We achieved the highest output power and lowest forward voltage values with the p-InGaN V-pit LED. The V-pits enhanced the light output power values by 1.45 times the values of the conventional LED owing to an enhancement of the light scattering probability and an effective reduction of Mg-acceptor activation energy. Moreover, this new technique effectively solved the higher forward voltage problem of the usual V-pit LED.

Insight into the interaction between Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode and BF4--introducing electrolyte at 4.5V high voltage

Owing to the high specific capacity and high voltage,Ni-rich(LiNi0.8Co0.1Mn0.1O2,LNCM811)cathode has been considered as one of the most promising candidate cathode materials for next generation lithium ion batteries,whereas severe capacity fading greatly hinders its practical application.Notably,the compatibility of Ni-rich materials with LiBF4-containing electrolyte has not yet been realized.Herein,1 M LiPF6-based electrolyte with introducing 2 M LiBF4 is proposed to dramatically improve the cyclic stability of high voltage LNCM811/Li half-cell.Addition of high concentrated LiBF4 improves the moisture stability of electrolyte,which hinders the generation of harmful by-product HF,resulting in improved interfacial stability of LNCM811.Lithium plating/stripping reaction of Li/Li symmetric cell confirms that the enhanced cyclic stability is ascribed to the improved interfacial stability of LNCM811 instead of lithium electrode.Morphology and composition characterization results reveal that LiBF4 participates in the CEI film-forming reaction,resulting in suppressed oxidation of electrolyte and interfacial structural destruction of LNCM811.

Effect of strain rate difference between inside and outside groove in M-K model on prediction of forming limit curve of Ti6Al4V at elevated temperatures

The influence of initial groove angle on strain rate inside and outside groove of Ti6Al4V alloy was investigated.Based on the evolution of strain rate inside and outside groove,the effect of strain rate difference on the evolution of normal stress and effective stress inside and outside groove was also analyzed.The results show that when linear loading path changes from uniaxial tension to equi-biaxial tension,the initial groove angle plays a weaker role in the evolution of strain rate in the M-K model.Due to the constraint of force equilibrium between inside and outside groove,the strain rate difference makes the normal stress inside groove firstly decrease and then increase during calculation,which makes the prediction algorithm of forming limit convergent at elevated temperature.The decrease of normal stress inside groove is mainly caused by high temperature softening effect and the rotation of groove,while the increase of normal stress inside groove is mainly due to strain rate hardening effect.

Development of OPTO-LDR coupled timer based voltage to frequency converter

This paper describes the development of a timer based voltage to frequency converter(V FC).Timer LM555is used in astable multivibrator mode with two OPTO-LDRs(light dependent resistors)in the circuitry.The frequency of timer output waveform which is measured using a digital storage oscillator(DSO)is almost linearly proportional to the applied input voltage.Hence we obtain a linear relationship between the frequency of timer output waveform and the input voltage.Because of its quasi-digital output,the main advantages of this developed converter are linear input-output relationship,small size,easy portabilityand high cost performance.In addition,the timer output waveform can be directly interfaced with personal computer or microprocessor/microcontroller for further processing of the input voltage signal without intervening any analog-to-digital converter(ADC).

Automated Multi-Meter Method for the Scaling of Low AC Voltage from 200 mV to 2 mV

A set of seven single junction thermal converter Micropotentiometers (μPots) has been constructed at the National Institute for Standards (NIS), Egypt. This set has been built to cover the low ac voltage ranges from 2 mV to 200 mV at frequencies from 40 Hz up to 20 kHz. The construction of the μPots set has been presented and an adopted calibration method has been performed as well. This method has been performed by means of a step-down procedure using a Digital Multi-Meter (DMM). The scaling procedures have been carried out in sequential steps starting from the calibration of the 200 mV-μpot by using DMM that is accurately calibrated at its 200 mV ac voltage range down to 2 mV-μPot. Furthermore, a new automatic calibration system has been established to achieve the scaling procedures. This system has been specially designed using Laboratory Virtual Instrument Engineering Workbench (LabVIEW) software to overcome the deficiencies of manual methods. The automatic calibration has been investigated of all mPots at different frequencies. The ac-dc differences for the μPots and their uncertainty evaluation from 2 mV to 200 mV at different frequencies from 40 Hz to 20 kHz have been determined.

适用于光导开关触发的V/N气体开关设计与验证

为了满足多路精确同步触发开关要求,将光导开关(PCSS)与V/N气体开关结合,可充分发挥PCSS低触发阈值、低抖动和光电隔离以及V/N气体开关工作电压高、带载能力强等优势。两种开关结合的核心是V/N气体开关结构参数与PCSS触发回路的参数匹配。分析计算了V/N气体开关的结构电容、触发回路振荡参数、开关电场分布等,研究了V/N气体开关的结构电容与PCSS、串联电感等构成的振荡回路的匹配关系,通过实验获得了V/N气体开关自击穿电压曲线、导通延迟时间以及不同欠压比下的延迟时间抖动等,初步验证了适用于PCSS触发的V/N气体开关设计。

Dynamic electrostatic-discharge path investigation relied on different impact energies in metal-oxide-semiconductor circuits

Gate-grounded n-channel metal-oxide-semiconductor(GGNMOS)devices have been widely implemented as power clamps to protect semiconductor devices from electrostatic discharge stress owing to their simple construction,easy triggering,and low power dissipation.We present a novel I-V characterization of the GGNMOS used as the power clamp in complementary metal-oxide-semiconductor circuits as a result of switching the ESD paths under different impact energies.This special effect could cause an unexpected latch-up or pre-failure phenomenon in some applications with relatively large capacitances from power supply to power ground,and thus should be urgently analyzed and resolved.Transmission-linepulse,human-body-modal,and light-emission tests were performed to explore the root cause.

特高压直流输电线路直线塔V型悬垂绝缘子串选型

在特高压直流输电线路工程中,直线塔通常采用导线V型悬垂绝缘子串,由于该金具串形式多样,受力复杂,在选型时往往又存在粗放设计的情况,因此会使工程存在一定的资源浪费情况。文章利用受力平衡原理对直线塔V型悬垂绝缘子串选型的数学模型进行分析,得到V型悬垂绝缘子串选型计算方法,给出计算程序编写流程图,将程序应用于某±800 kV特高压直流输电线路工程中,验证了该方法的正确性和可行性。

V型球阀的米浆流量实验研究

建立一种符合实际生产的米浆流量模型对提高米粉生产标准化至关重要。对比以往的一次函数、二次函数和指数函数孔口流量模型,提出一种幂函数孔口流量模型,利用软件Origin的LMA算法的非线性最小二乘法拟合4种函数流量模型。结果表明:4种模型均通过了卡方检验及F检验,幂函数的调整R平方最高且残差平方和最小,说明幂函数流量模型拟合效果最好。为孔口流量模型提供了一种新的幂函数参考。

500 kV变电站直流融冰装置参数设计标准差异对比研究

针对变电站直流融冰装置参数工程设计问题,比较和分析不同标准、规范关于融冰电流计算公式的差异,以某500 kV变电站实际工程直流融冰装置参数设计为例,按照不同计算公式给出了最小融冰电流、最大融冰电流、1 h融冰电流、直流融冰压降、直流融冰装置容量等参数计算结果;通过对比分析给出实际工程中融冰装置参数设计公式选用的建议。

无源无线多功能传感器在低压600 V系统中的应用研究

该文提出了一种无源无线多功能传感器,能够利用电缆周围的电磁能量和热能进行供电,同时测量电缆的温度值和电流值,根据电缆的带电状态进行判断和报警。详细介绍该传感器的原理、结构、技术细节和工作流程,并以特高压换流站伴热带为例,展示该传感器的应用方案和效果。实验结果表明,该传感器能够实现对电缆的实时监测和分析,提高电缆运行的安全性和可靠性,节约能源和成本,简化安装和维护,适用于各种环境,具有较高的创新性和实用性。

改进型三相V/v牵引变压器及其综合补偿方法

三相V/v变压器在高速铁路中广泛使用。高速电力机车作为单相PWM负载,在电网产生严重的负序、3次谐波和频带较宽的高次谐波电流。该文提出由三相三绕组V/v变压器、无源滤波器和三相电压源逆变器(voltage source inverter,VSC)组成的综合补偿系统。三相V/v变压器带补偿绕组,补偿绕组采用零等值阻抗设计,直接匹配为VSC电压等级,省去两台降压变压器;无源滤波器采用感应滤波技术设计,包括3次单调谐滤波器和高通滤波器;VSC仅补偿负序电流,降低了开关频率。详细阐述了系统方案,利用等效电路分析基于感应滤波技术的谐波抑制原理,得出滤波器设计方法,推导负序电流补偿原理,并提出一种新的参考电流检测算法。该算法避免了检测网侧相电压而三相V/v变压器无网侧中性点的矛盾,采用准比例谐振VSC控制方法,在电网频率波动时仍有良好的电流跟踪效果。仿真与实验结果验证了所提方案和控制方法的正确性。

一种新的差值SVPWM调制方法

通过对传统SVPWM调制算法进行理论分析和算法推导,提出了一种新的差值SVPWM调制方法。该方法在每个控制周期内,直接采用三相电压差值来计算基本电压矢量作用时间,并由相电压之间从大到小排序来判定扇区,省去了传统实现方法中复杂的坐标矩阵变换、三角函数计算等矢量分解过程,简化了SVPWM算法步骤。进一步的仿真与实验,证明了该差值SVPWM算法正确、计算效率高、实时性强,节省CPU资源。

新型感应电机V/F控制系统稳定性方法

针对感应电机V／F控制系统在空载或轻裁时存在一个持续振荡的稳定性问题，提出一种改善感应电机V／F控制系统稳定性的方法。根据感应电机的数学模型，研究了系统振荡与无功电流波动之间的关系。并基于定子电压定向对电流进行分解，通过控制无功电流恒定调节输出电压来抑制电机振荡，提高系统的稳定性。实验结果表明：该方法不依赖电机参数，鲁棒性高，使系统在0～50Hz内都能平稳运行，电机的振荡得到了抑制，有效地提高了系统的稳定性。

基于V形曲线的定子电流限制改进方法

首先通过分析现有典型定子电流限制器动作对系统电压稳定的影响,指明其存在无法保护发电机主设备安全且加剧系统电压崩溃的隐形缺陷。然后基于单机无穷大系统V形曲线特性分析,提出利用发电机机端功率因数角小于系统外功角识别发电机定子电流最小值点的判据,并给出改善定子电流限制涉网特性的控制方法及系统阻抗整定建议。最后,通过实际装置的测试结果验证了所提定子电流限制优化方法的有效性。

一种基于V-I特性的节点电压稳定快速判断方法

将简单系统基于V-I特性的电压稳定判别法成功地应用于复杂系统,推导出了判断负荷节点静态电压稳定性的公式。只需对系统进行两次常规潮流计算,即可根据公式迅速判断系统每一个节点的电压稳定性,同时计算出各个节点的电压稳定裕度。该方法简单、快速,可用于实时在线判断电压稳定性、确定系统的薄弱节点和薄弱区域,为分析控制电压稳定提供指导。系统算例验证了该方法的有效性。

1100kV变压器套管抗震性能研究

通过对某型1 100 kV变压器套管(A型)的抗震计算,发现瓷件圆弧处的应力比瓷根部直线部分的应力大的现象。在另一种结构的1 100 kV变压器套管(B型)的抗震试验中,证实了计算中遇见的瓷件圆弧处的应力比直线部分应力大的现象,因此仅以瓷根处直线部分的应力作为抗震试验通过与否的标准并不准确,如何判断抗震试验是否通过还需进一步的探讨。

基于恒定导通时间的V^2控制方法研究

恒定导通时间控制的Buck电路瞬态响应速度快,控制电路简单,但其电压调整率差,影响了其在电压调整模块(VRM)中的应用。为了提高其电压调整率,本文首先分析了基于恒定导通时间控制的Buck电路电压调整率差的原因,提出并分析了基于恒定导通时间的V2控制,通过仿真和实验对比了这两种控制方法,结果证明了基于恒定导通时间的V2控制方法具有快速的瞬态响应,而且提高了电压调整率,与恒定导通时间控制相比更适合应用在电压调整模块中。

一种用于V形钳位多电平变换器的IGBT吸收电路方案

只有公共直流侧电容的V形钳位多电平变换器(VMC)在中压、大功率电能变换的场合具备良好的应用价值。但当VMC电平数较高时,其换流回路电感不可避免地增大,使IGBT开关器件的关断过电压问题凸显。为此,该文提出一种简单的VMC吸收电路方案。依据VMC的运行原理,将其开关器件区分为主开关器件和辅助开关器件。主开关器件动作并切换电流通路,在每一对互补的主开关器件两端添加吸收电容(构成类似半桥开关能量缓冲单元),以抑制其关断过电压。而主开关器件相对应的辅助开关器件则先开通、后关断,仅提供静态电压支撑的功能,因此无需吸收电路保护。该文以七电平VMC为例,对所提的吸收电路方案进行了分析和研究。实验结果表明,所提的VMC吸收电路方案能够显著抑制开关器件的关断电压尖峰。并且,该方案仅需少量吸收电容与主开关一起构成类似半桥开关能量缓冲单元的形式即可实现所有开关器件的关断过电压保护,其成本低、可靠性高,具有良好的工程实用性。

特高压变电站带跳线V形耐张瓷绝缘子串的均压特性

1000 kV特高压交流试验示范工程变电站内均采用盘形瓷绝缘子串。由于特高压变电站电压等级高,上下层构架复杂,且绝缘子串组装形式多样,导线排布方式各异,导致上下层构架之间以及相与相之间相互均存在一定的影响,因此使得绝缘子串的分布电压和高压侧的电场分布极不均匀,需要对其均压特性进行研究。为此,运用三维有限元法,考虑了跳线、均压环等金具、上下层构架塔之间和三相相互的影响,仿真计算了1000 kV变电站内带跳线V形耐张瓷绝缘子串的电位和电场分布,研究了均压环对其均压特性的影响,并对均压环结构形式和配置参数进行了优化,给出了适用于带跳线V形耐张瓷绝缘子串的均压环配置方案。该研究成果对提高1000 kV交流变电站绝缘子的安全运行可靠性具有重要意义,已经成功应用于我国特高压交流试验示范工程,效果良好。