共查询到20条相似文献,搜索用时 31 毫秒
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光伏组件热斑对发电性能的影响 总被引:1,自引:0,他引:1
针对光伏电池上的热斑问题,分析了热斑生成的原因和对发电性能的影响,介绍了红外热像仪检测热斑的方法,并探讨了用旁路二极管解决热斑危害的可能性,以提高光伏电池组件的寿命。 相似文献
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针对三维有限元方法分析轴向磁场盘式开关磁阻电机时计算机配置要求高、耗时长及不适于电机的优化设计和基于定转子极中心线对齐位置和定子极中心线和转子槽中心线对齐位置这两个关键位置的磁路法计算精确度不高等问题,对转子齿前沿和定子齿前沿重叠位置即临界重叠位置处磁化曲线进行解析计算.利用三相6/4极和12/8极轴向磁场盘式开关磁阻电机的有限元仿真结果及磁阻最小原理划分该位置处磁链并进行计算,推导出该种电机临界重叠位置处磁化曲线,并与三维有限元方法的计算结果进行对比.分析结果表明,此种解析法的计算精确度符合要求.计算结果验证了解析分析计算的正确性. 相似文献
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Kawano K. Kohtoku M. Okamoto H. Itaya Y. Naganuma M. 《IEEE journal of selected topics in quantum electronics》1997,3(6):1351-1360
The coupling and conversion characteristics of four types of spot-size converter integrated laser diodes (SS-LDs) to a single-mode fiber (SMF) in the 1.3-μm-wavelength region are numerically clarified. The SS-LDs are categorized into types with vertical tapers and types with a combination of a lateral taper and a thin-film core. The eigenmodes are obtained by the finite-element method (FEM). The semivectorial 3-D finite-difference (FD) beam propagation method (BPM) is used to calculate the propagating beams 相似文献
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Musumeci S. Raciti A. Frisina F. Melito M. Saggio M.G. 《Industry Applications, IEEE Transactions on》2007,43(3):636-647
In this paper, standard-cell Schottky rectifiers along with silicon-based merged p-i-n-Schottky (MPS) and p-i-n diodes, which are realized using a super junction technology, have been analyzed and compared by conducting extensive device and mixed-mode simulations through a 2-D finite-element grid. The main issues that concern these devices, such as the forward voltage drop, the leakage characteristic, and the reverse recovery, are treated, and the superior performances exhibited by the MPS rectifier with respect to the p-i-n diodes are experimentally validated. First, the basics on the used technology are reported by focusing on the high voltage capability of the new devices along with the low forward voltage drop during the on -state conduction. The reverse-recovery behavior belonging to the MPS diode has been analyzed by exploring through several simulations the internal plasma dynamics. 2-D simulations of the turn-on behavior relative to the Schottky, p-i-n, and MPS rectifiers have been carried out in order to analyze the effects of the voltage overshoot phenomenon eventually occurring in the three diode structures 相似文献
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红外热成像技术是一种探测与识别目标温度的重要手段。由于目前红外热像仪均采用红外焦平面传感器作为成像核心部件,其成本极其高昂且工作独立性差。针对上述问题,采用阵列式红外传感器作为核心部件,以ARM作为计算协处理单元,以FPGA作为图像核心处理单元,通过设计基于温度值的灰度图像生成与增强算法,在保证实现系统功能的同时降低了系统的复杂度和成本。实验结果表明系统测温精度可达0.1℃,刷新帧率稳定在30Hz,验证了算法的有效性和系统设计的合理性。 相似文献
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Charalambos M. Andreou Julius Georgiou 《International Journal of Circuit Theory and Applications》2016,44(5):1029-1038
A low‐voltage, low‐power, low‐area, wide‐temperature‐range CMOS voltage reference is presented. The proposed reference circuit achieves a measured temperature drift of 15 ppm/°C for an extremely wide temperature range of 190 °C (?60 to 130 °C) while consuming only 4 μW at 0.75 V. It performs a high‐order curvature correction of the reference voltage while consisting of only CMOS transistors operating in subthreshold and polysilicon resistors, without utilizing any diodes or external components such as compensating capacitors. A trade‐off of this circuit topology, in its current form, is the high line sensitivity. The design was fabricated using TowerJazz semiconductor's 0.18‐µm standard CMOS technology and occupies an area of 0.039 mm2. The proposed reference circuit is suitable for high‐precision, low‐energy‐budget applications, such as mobile systems, wearable electronics, and energy harvesting systems. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Improved output performance of high-power VCSELs 总被引:5,自引:0,他引:5
Miller M. Grabherr M. King R. Jager R. Michalzik R. Ebeling K.J. 《IEEE journal of selected topics in quantum electronics》2001,7(2):210-216
The intention of this paper is to report on state-of-the-art high-power vertical-cavity surface-emitting laser diodes (VCSELs), single devices as well as two-dimensional (2-D) arrays. Both approaches are studied in terms of electrooptical characteristics, beam performance, and scaling behavior. The maximum continuous wave (CW) output power at room temperature of large-area bottom-emitting devices with active diameters up to 320 μm is as high as 0.89 W, which is to our knowledge the highest value reported for a single device. Measurements under pulsed conditions show more than 10-W optical peak output power. Also, the CW performance of 2-D arrays has been increased from 0.56 W for 23 elements to 1.55 W for 19 elements due to significantly improved heat sinking. The extracted power densities spatially averaged over the area close to the honeycomb-like array arrangement raised from 0.33 kW/cm2 to 1.25 kW/cm2. Lifetime measurements have proven acceptable reliability for over 10000 h at a degradation rate of less than 1% per 1000 h. The emission wavelength of bottom-emitting devices is restricted to about 900 nm or higher due to fundamental absorption in the GaAs substrate. Windowing of the substrate has been studied to allow for shorter wavelength emission 相似文献
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975-nm single-mode laser source: external coherent combining of two pigtailed laser diodes 总被引:3,自引:0,他引:3
Sabourdy D. Desfarges-Berthelemot A. Kermene V. Barthelemy A. 《IEEE journal of selected topics in quantum electronics》2004,10(5):1033-1038
We report on the efficient coherent combining up to 85% of two single-mode fiber coupled laser diodes emitting at 975 nm. The combining is performed by an external feedback on the two laser diode cavities through an all-fiber interferometric arrangement based on standard components. 相似文献
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Uchida S. Takeya M. Ikeda S. Mizuno T. Fujimoto T. Matsumoto O. Goto S. Tojyo T. Ikeda M. 《IEEE journal of selected topics in quantum electronics》2003,9(5):1252-1259
The property of GaInN-AlGaN heterostructures and GaInN multiple quantum well (MQW) gain GaInN laser diodes with low internal loss are described. GaInN blue-violet laser diodes have been developed as a light source for optical disk recording. However, the threshold current density of these diodes has been difficult to reduce and remains high at around 3-4 kA/cm/sup 2/. This is thought to be due to the large transparency current density Jt and the large optical internal loss /spl alpha//sub i/. Recently, the internal loss was successfully reduced to 13.6 cm/sup -1/ by optimizing the design of the near active region and achieved stable continuous operation under 50-mW continuous wave at 70/spl deg/C. Other laser characteristics such as far-field patterns and laser noise have also been improved for optical disk use. 相似文献
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Dustin A Heldman Wei Wang Sherwin S Chan Daniel W Moran 《IEEE transactions on neural systems and rehabilitation engineering》2006,14(2):180-183
In this paper, intracortical local field potentials (LFPs) and single units were recorded from the motor cortices of monkeys (Macaca fascicularis) while they preformed a standard three-dimensional (3-D) center-out reaching task. During the center-out task, the subjects held their hands at the location of a central target and then reached to one of eight peripheral targets forming the corners of a virtual cube. The spectral amplitudes of the recorded LFPs were calculated, with the high-frequency LFP (HF-LFP) defined as the average spectral amplitude change from baseline from 60 to 200 Hz. A 3-D linear regression across the eight center-out targets revealed that approximately 6% of the beta LFPs (18-26 Hz) and 18% of the HF-LFPs were tuned for velocity (p-value < 0.05), while 10% of the beta LFPs and 15% of the HF-LFPs were tuned for position. These results suggest that a multidegree-of-freedom brain-machine interface is possible using high-frequency LFP recordings in motor cortex. 相似文献
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基于计算机视觉的金属板带材表面缺陷检测是冶金工业领域的研究热点,金属板带材制造行业对其表面质量的高标准要求自动化视觉检测系统及其算法性能不断提升。通过回顾关于钢板钢带、铝板铝带和铜板铜带等典型金属板带材产品的110余篇文献,对基于二维和三维机器视觉的表面检测技术进行了系统综述。根据算法性质和图像特征,将现有二维缺陷检测技术分为基于统计、谱、模型和机器学习的4类方法,根据三维数据获取方式,将三维缺陷检测技术分为立体视觉测量、激光扫描仪测量法和结构光测量方法。对经典算法和新近方法进行了介绍、分析和比较。最后,对缺陷视觉检测仍存在的挑战和未来研究趋势进行了讨论与展望。 相似文献
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《Device and Materials Reliability, IEEE Transactions on》2009,9(4):557-562
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Nielsen P. Blaabjerg F. Pedersen J.K. 《Industry Applications, IEEE Transactions on》1999,35(5):1150-1161
Induction motors are traditionally controlled by standard pulsewidth modulation voltage-source inverters. An alternative is the matrix converter, which consists of nine bidirectional switches. This converter has benefits compared to a standard inverter, like sinusoidal input current and bidirectional power flow. The main disadvantage is the lack of a bidirectional switch, because such a switch may be done by two transistors and two diodes. An important topic is protection of the matrix converter, and this paper proposes two new protection circuits for matrix converters with a reduced number of components. The number of protection diodes is reduced by six. Design expressions of the protection circuit are calculated and validated by simulation. The standard protection circuit and the new circuits are demonstrated by simulation to have the same performance. Experimental results on an 8 kVA matrix converter show the design expressions are correct. It is concluded that it is possible to reduce the necessary power components in a matrix converter 相似文献
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Kanhere N.K. Birchfield S.T. 《Intelligent Transportation Systems, IEEE Transactions on》2008,9(1):148-160
We present a method for segmenting and tracking vehicles on highways using a camera that is relatively low to the ground. At such low angles, 3-D perspective effects cause significant changes in appearance over time, as well as severe occlusions by vehicles in neighboring lanes. Traditional approaches to occlusion reasoning assume that the vehicles initially appear well separated in the image; however, in our sequences, it is not uncommon for vehicles to enter the scene partially occluded and remain so throughout. By utilizing a 3-D perspective mapping from the scene to the image, along with a plumb line projection, we are able to distinguish a subset of features whose 3-D coordinates can be accurately estimated. These features are then grouped to yield the number and locations of the vehicles, and standard feature tracking is used to maintain the locations of the vehicles over time. Additional features are then assigned to these groups and used to classify vehicles as cars or trucks. Our technique uses a single grayscale camera beside the road, incrementally processes image frames, works in real time, and produces vehicle counts with over 90% accuracy on challenging sequences. 相似文献
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Kawano K. Kohtoku M. Wada M. Okamoto H. Itaya Y. Naganuma M. 《IEEE journal of selected topics in quantum electronics》1996,2(2):348-354
In order to develop spotsize-converter-integrated laser diodes (SS-LDs) with high efficiency and large-misalignment tolerances in the 13-μm-wavelength region, spotsize converters (SSCs), which consist of lateral taper, thin-film core and ridge, are investigated employing the three-dimensional (3-D) semivectorial finite-difference beam propagation method (FD-BPM) with nonequidistant discretization. The sum of the spot-conversion loss and coupling loss between the laser diode (LD) eigenmode and the single-mode fiber (SMF) eigenmode are calculated for various structural parameters. Small loss of around 1.5 dB can be achieved by introducing a nonlinear taper. The fabrication tolerances for the SSCs are also clarified. The calculated results agree well with the results for actually fabricated SS-LD's. It is also shown that the radiation loss and coupling characteristics of the SS-LDs with a buried thin-film core structure can be improved using a nonlinear taper 相似文献