100kA快响应精密冲击分流器研制及特性分析

冲击电流为暂态电流波形,持续时间短且波形不可重复,测量误差影响因素众多难以评估。研制快响应精密冲击分流器,采用同轴管式结构,分析分流器的测量原理及尺寸设计。研究分流器的瞬态响应过程,将输出信号焊接至电阻体外侧,消除趋肤效应的影响。分流器的稳态电阻测量值为0.9697mΩ,杂散电感为32nH,测量额定电流时,电阻温升小于36℃。研制方波电流源测量分流器的动态特性,阶跃响应时间小于4ns,并利用卷积积分的方法计算动态特性引起的峰值和时间参数测量误差。冲击电流波形8/20μs下,进行分流器线性度、稳定性等特性试验。研究冲击电流测量装置的不确定度评定方法,分析不确定度影响因素,峰值参数测量不确定度为0.4%(k=2),时间参数测量不确定度0.8%(k=2)。说明该测量装置可作为标准测量装置用于电流传感器的校准。     

智能型冲击峰值电压电流表的设计

由于目前国内外生产的测量冲击电压峰值的峰值表,其准确度为1%~3%,不能满足最新国家标准的要求,所以,要研制更高等级的冲击峰值电压电流表(以下简称峰值表)。该设计主要由输入衰减器、正反相极性峰值检波采样保持电路、A/D转换器(7135型芯片)、单片机系统、触摸液晶显示屏、锁存保持电路、复位/测量设置电路以及供电电源等部分组成。该设计可以直接测量其峰值电压不大于2kV的冲击电压,当外接用于测量冲击电流的同轴分流器时,被测的冲击电流通过分流器实现电流/电压转换,将冲击电流转化为冲击电压,实现测量峰值电流的功能。经过稳定性考核,可以分析得出准确度可以达到0.5%,完全满足实际使用的要求。     

电流监测器灵敏度误差的校准

提出以无感电阻为标准器,电流通过电流监测器及无感标准电阻,监测器输出端电压与无感标准电阻两端的电压差由示波器测得,即为电流监测器灵敏度的误差。以型号为2100的电流监测器为例,分别对稳态电流信号和暂态电流信号下监测器的灵敏度误差进行了校准。     

雷电冲击电流测试系统研究

目的 研究雷电冲击电流测试系统，方法 用无感电阻网络分流器测量雷电冲击电流，并进测量重复性、线性度试验和阶跃波响应试验。结果与结论 所研制的无感电阻网络分流器符合国家标准GB/T7626.5-1999和国际电工委员会标准IEC61000-4-5的要求，且可用于KV级脉冲大电流的测量和雷电浪涌（冲击）模拟器短路电流的波形校准。     

基于采样原理的直流电能表校准装置

介绍了一套自行研制的直流电能表校准装置,对输出的直流功率信号中的电压、电流分别变换后进行采样并卷积,得到一段时间内的平均功率标准值,采用相同的外触发信号同步采样测量被检直流电能表的脉冲输出,得到与被检直流电能表输出相关的频率值,并用LabVIEW编写了自动测试计算软件得到测量结果。该方法利用3458A数字多用表直流信号采样准确度高的特性,有效地克服了测量信号稳定性、测量噪声和分流器发热不稳对测量结果的影响,为建立高准确度的标准直流电能表校准装置提供了一种技术解决方案,为直流电能量值溯源提供了技术保障。     

并网供电模拟系统

本装置核心部分由两个额定输出功率均为16W的8VDC/DC模块并联构成,利用电压、电流负反馈来调节两支路电流的大小和比例,稳定输出电压。利用霍尔电流传感器采样两支路电流大小,利用精密分压电阻采样输出电压,传送到控制部分(MCU)进行计算、判断,控制部分输出PWM控制信号到DC/DC模块输入端,来实现调节模块输出的目的。     

电网功率因数监测模拟装置

设计了一种电网功率因数模拟监测装置。该装置以AT89C51单片机为核心,通过采集交流电流电压波形之间的相位差来得到电路功率因数。首先对被测电路的电压、电流进行采样,通过整流电路将正弦波信号转化为方波信号,再将两方波信号送入双D触发器中,输出得到一路整合的方波,然后检测出一个周期内该方波的上升沿与下降沿,同时启动定时器计数,那么上升沿与下降沿之间定时器的计数值经过换算即可得到电压与电流的相位差,最后利用单片机计算出功率因数。实践表明该方案测量方便,结果可靠,易于实现。     

基于LabVIEW的脉冲大电流测试系统

基于图形化编程语言Lab VIEW,采用高速采样算法,搭建了脉冲大电流测试系统。系统主要通过程序控制数字多用表等仪器对同轴分流器上脉冲电压的参数进行数据采样,计算得到脉冲大电流具体参数。该系统同时考虑了采样时延、采样速率等因素,降低了测量不确定度。经实验验证,本测试系统可靠性强,测量准确度高。     

利用真有效值交流电压表和A40分流器测量交流电流

本文介绍了利用A40系列分流器和具有交流电压真有效值测量功能的数字多用表通过与直流标准电流的比较得到被测交流电流的实际值 ,解决了使用传统热转换标准测量交流电流工作效率低、测量范围窄和操作过程复杂等问题。     

数字微差补偿器及其在电流比较仪电桥中的应用

设计一种能够在四象限内对输出信号进行调节的数字微差补偿器,核心器件为16 位串行输入乘法型数模转换器,以正弦电压信号作为参考,可根据接收的数字编码分别调节输出补偿信号的同相分量和正交分量。提出一款计算机控制的电流比较仪电桥线路,应用数字微差补偿器和牛顿迭代算法实现电流比较仪磁势的自动平衡。利用研制的电桥对双螺线型计算电阻进行测量,结果表明,该电桥在1592 Hz频率范围内的标准测量不确定度为2×10^-7,能够满足交流电阻量值传递要求。     

基于高低压电源切换的双环恒流控制电磁流量计励磁控制系统

为了提高电磁流量计高频方波励磁性能,基于励磁恒流控制仿真分析,采用外环高低压电源切换和内环电流微调的双环励磁恒流控制方式,以保证电磁流量计高频方波励磁时一次仪表输出信号零点稳定、电源利用效率高。设计方波励磁控制系统,以实现高频方波精确励磁。仿真结果表明,高压源电压越高越有利于拓宽励磁频率范围。实验结果表明,系统在高频方波励磁时,励磁电流响应速度快且电磁流量计传感器输出信号零点稳定。     

照明用大功率无桥LED驱动电路输入电流谐波分析

对作者介绍的照明用大功率无桥LED驱动电路的输入交流工频电流波形在设定电路条件后的频谱和谐波含量进行了分析和计算,其结果是,在电路最低工作频率以下的频率范围内基本不存在谐波成分,电路输入电流的总谐波含量THD随最小输入电流脉冲宽度T₀(min) 增大而上升,随电路的输出直流电压与输入交流电压有效值的比U_o/U_i的增大而下降.并指出在电路的输入端需要一个滤波电路,分析了滤波电路的滤波效果,给出了滤波电路的设计方法.     

基于改进型匹配网络的宽带高效率E类功放的设计

为了解决E类功放工作带宽过窄的问题,对E类功放的输入、输出匹配网络提出了一种改进方案.该方案中输出匹配网络采用微带线结构与切比雪夫低通匹配网络相结合的方法,在较宽的工作带宽内有效地抑制了谐波;并采用阻抗变换方法设计了含闭式解的宽带带通输入匹配网络,明显增强了输入匹配网络设计的灵活性.利用该方案,同时采用多谐波双向牵引技术得到功率管的最佳源阻抗和负载阻抗,基于CGH40010F功率管设计了一款应用于L波段的宽带高效率E类功放.测试结果表明,在输入功率为28dBm,漏极偏置电压VDS=28V,栅极电压VGS=-3.3V时,在整个L波段频率范围内漏极工作效率大于65%,最高达到83%,输出功率为39~41.1dBm,增益为11~13.1dB,增益平坦度为±1dB.这一结果验证了该改进方案的有效性,使得E类功放具有宽带宽、高效率的性能.     

Proposal of DC shield reactor type superconducting fault current limiter

Saturated DC reactor type superconducting fault current limiter (SFCL) had been proposed two years ago. It was classified to rectifier type SFCL. The changing inductance value with the operating mode has superior characteristics to reduce voltage sag during step increase of the load current. But it has the disadvantage of its weight. In this paper, rectifier type SFCL with shielded reactor has been proposed. The reactor which has superconducting ring or tube inside its winding is substituted to the DC link of the rectifier. The configuration looks like an air core transformer with secondary short winding. When the current through the bulk shield-ring reaches to a certain level, the flux penetrates to the shield body and finite impedance appears in the primary winding. In other words, when the surface flux density exceeds its critical flux density, the flux penetrates into the bulk superconductor, and increases equivalent inductance. The equivalent transient resistance of the shield was represented as a function of exponential of the time. Using this equivalent transient resistance, the transient impedance was expressed. The transient wave analysis using EMTDC (electro-magnetic transients in DC systems) has been described. Simulated waveforms are shown considering the source inductance, the leakage inductance, the coupling coefficient and the forward voltage drop of the semiconductor. And voltage sag was also investigated with 50% step load increase.Preliminary design was also performed. The coil size and number of turns are designed to obtain adequate inductance for the current limitation, and the central magnetic field of the coils are calculated. There is optimal aspect ratio to minimize the magnetic field with restriction in outer diameter of the coil.     

不同负载对太阳能电池输出功率的影响

利用直流电子负载对太阳能电池进行了恒压、恒流和恒阻三种模式下的测试,得到了太阳能电池的输出功率响应曲线,又用陶瓷电阻进行了恒阻模式下的测试和对比.实验结果表明,太阳能电池的输出特性随不同类型的负载变化趋势基本一致.通过比较得出了在利用直流电子负载进行太阳能电池特性测试时,恒压、恒流模式下的测试结果比较可信,恒阻模式下的测试结果存在突变现象,输出响应存在问题,不推荐使用;而在纯电阻的恒阻模式下,太阳能电池的输出特性与恒压、恒流模式下的测试结果一样可信.     

Chopped Radiation Measurements With Large Area Si Photodiodes

Frequency dependent response characteristics of photocurrent meters using large area, radiometric quality Si photodiodes have been analyzed. The current responsivity, the voltage noise and drift amplification, and the gain and bandwidth of the photocurrent-measuring analog control loop were calculated. The photodiodes were selected for high shunt resistance. The effect of the photodiode junction capacitance on the response characteristics was also analyzed. As a result of photocurrent gain dependent frequency compensations, the noise boosting effect was minimized at the output of the current meter. The loop gain and bandwidth were maximized. High-accuracy photocurrent measurements can be achieved using the described procedures for both dc and modulated optical radiation.     

Harmonic reduction in capacitive micromachined ultrasonic transducers by gap feedback linearization

The nonlinear relationship between the electrical input signal and electrostatic force acting on the capacitive micromachined ultrasonic transducer (CMUT) membrane limits its harmonic imaging performance. Several input shaping methods were proposed to compensate for the nonlinearity originating from the electrostatic force's dependence on the square of the applied voltage. Here, we analyze harmonic generation in CMUTs with a time-domain model. The model explains the basis of the input shaping methods and suggests that the nonlinearity resulting from gap dependence of the electrostatic force is also significant. It also suggests that the harmonic distortion in the output pressure can be eliminated by subharmonic ac-only excitation of the CMUT in addition to scaling the input voltage with the instantaneous gap. This gap feedback configuration can be approximated by the simple addition of a series impedance to the CMUT capacitance. We analyze several types of series impedance feedback topologies for gap feedback linearization. We show that for subharmonic ac excitation, although resistive and capacitive impedances result in a trade-off between input voltage and harmonic distortion for a desired pressure output, harmonic generation can be suppressed while increasing the Pa/V transmit sensitivity for proper series inductance and resistance feedback. We experimentally demonstrate the feedback method by reducing harmonic generation by 10 dB for the same output pressure at the fundamental frequency by using a simple series resistor feedback with a CMUT operating at a center frequency of 3 MHz. The proposed methods also allow for utilization of the full CMUT gap for transmit operation and, hence, should be useful in high-intensity ultrasonic applications in addition to harmonic imaging.     

蓄电池内阻测量及其去干扰方法研究

为测试蓄电池的欧姆内阻和极化内阻,并提高其测量精度,提出一种由方波发生器构成的测试电路进行测试的方法。为消除浮充状态下充电器纹波电压对内阻测量数据的干扰,提出一种欧姆内阻测量的抑制纹波电压干扰的方法,即对多个测量数据求平均值的方法。欧姆内阻测量方法的特点是:不必等测试电路达到稳态,因而节省测试时间,避免能量浪费;与传统的测量方法相比,采用较小的测试电流即可获得精确的欧姆内阻测量结果。