融合前沿研究的液体电介质击穿教学研究

针对《高电压与绝缘技术》课程中液体电介质的教学难点，提出了融合前沿研究的液体电介质击穿教学方法。基于前沿的液体放电应用背景与先进的液体放电研究平台，形象地展示液体电介质的动态击穿过程，在教学内容、教学方法、考核方式等方面进行科教融合改进，实施“以学生为中心”理念的课程教学设计。该教学方式取得了较好的教学效果，能够为其它知识点的教学质量提升提供参考。     

基于小波时频图和卷积神经网络的断路器故障诊断分析

高压断路器操动机构振动信号为非平稳性信号,蕴含着丰富的操动机构工作状态的信息,对操动机构工作状态的检验辨识具有重大意义。提出一种基于小波时频图和卷积神经网络的断路器故障诊断方法。对操动机构振动信号进行连续小波变换生成时频图(CWT),并对时频图进行统一压缩预处理;将预处理后的时频图作为特征图输入卷积神经网络AlexNet模型;通过对网络参数的调整,逐步改进网络模型,有监督地实现对操动机构故障状态的辨识诊断。结果表明,该方法能够有效地运用于断路器操动机构故障辨识诊断,与小波频带能量-RBF、小波频带能量-SVM的故障识别相比,故障识别准确率最高。     

Experimental investigation on the voltage uniformity for a PEMFC stack with different dynamic loading strategies

The operating life of the proton exchange membrane fuel cell stack is mainly decided by performances of its weakest single cell because of the “Buckets effect”, thus high voltage uniformity during a dynamic loading process is key to the stack durability. In this work, a 3-kW stack is examined experimentally on its voltage uniformity (voltage coefficient variation (Cv)) under conditions of loading from open-circuit state (0 A) to nominal current (165 A) and stack temperatures of 30 °C, 45 °C and 65 °C. Different dynamic loading strategies, namely constant loading rate strategy, decreasing loading rate strategy, and increasing loading rate (square/cube increasing loading rate) strategy, are examined and compared. Results display that during the loading process, (a) the voltage uniformity rises abruptly and goes down quickly when the loading current is small (e.g. from 0 A to 22 A), (b) the voltage uniformity under a small loading current is better than that under the open-circuit state, and (c) voltage uniformity decreases as the loading current increases from a small value to the nominal current. Comparisons of different current loading strategies show that as the stack temperature rises from 30 °C to 65 °C, the stack Cv value under the open-circuit state increases from 1.12 to 1.84 and decreases from 3.85 to 2.45 in the nominal current state. The maximum Cv for the decreasing loading rate strategy decreases from 16.25 to 9.49 and that of the constant loading rate strategy also decreases from 5.85 to 4.96. Cv values of the square current increasing loading rate strategy keep below 3.85 under conditions of the three stack temperatures and display a slight fluctuation during the whole current loading process, which indicates that the strategy can effectively make the stack being of an excellent voltage uniformity during the instantaneous response process.     

车门内饰板优化分析及模具设计

利用CAE分析软件Moldex3D先找出整个设计是否存在缺陷,为了增加优化效率,采用田口实验设计法规划控制因子与配置。L9(34)直交表来求得成型条件的最佳化参数组别,观察结果并找出最佳成型条件,以降低成型后所发生的体积收缩率以及翘曲位移量。由S/N因子反应表可看出对于Z轴变形量在塑料温度209℃、保压时间11.025 s、冷却时间17.85 s时较优良。Z轴的翘曲从1.64 mm降低到1.04 mm,整体改善了36.5%,最终根据优化结果进行了模具设计。     

小议经济型异构播出系统

电视播出系统的稳定性与安全性直接关系到电视播出的效果。结合实践经验,对经济型异构播出系统的构建进行介绍。     

电压降法在水平定向钻穿越管道外涂层评价中的应用研究

介绍了电流-电位法、电流密度法在水平定向钻穿越管道外涂层评价中的应用,联合电压降法计算管内电流值,并结合实际案例对穿越管道两端连头之后外涂层性能进行评价。     

基于经验模态分解方法的拉曼光谱信号处理研究

经验模态分解(EMD)方法是一个以信号内在物理频率成分为对象的自适应时频分析方法,而常见的非平稳信号分析方法,比如小波分析,它需要选择小波基,不同小波基的分析结果不同;拉曼光谱信号是典型的非线性和非平稳信号,EMD方法充分地保留了信号本身的非线性和非平稳的特征,适应于拉曼光谱信号的分析。实验在自行研制的拉曼光谱测试平台上获得了原始的拉曼光谱信号,并通过经验模态分解将信号分解成不同频率的10个本征模式分量,信号能量集中在750cm^-1和1500cm^-1左右,最后进行了频率成分分析和去噪处理,并和小波分析方法进行了对比,验证了EMD方法的有效性和实用性,该方法在拉曼光谱信号分析中有较好的应用前景。     

High performance multi-layer varistor (MLV) from doped ZnO nanopowders by water based tape casting: Rheology,sintering, microstructure and properties

In this work, we report the fabrication of a high performance multi-layer varistor (MLV) via water based tape casting method using novel compositions of nanomaterials. Bi₂O₃, CaO and Co₃O₄ doped ZnO nanopowders were prepared by solution combustion synthesis (SCS) route, calcined at different temperatures (550, 650, 750 and 850?°C) and characterized by TEM, XRD, SEM and AFM. The nanopowder (crystallite size ~30?nm) calcined at 650?°C for 1?h was used as the starting material for MLV fabrication. Compositions of the slurry containing doped ZnO nanopowders, binder and plasticizer in water solvent were optimized for the fabrication of thick film. The rheological properties of the slurries having different solid loadings were analysed and thick films of various thicknesses (50–500?µm) were prepared by varying the feeding rate of tape casting. The film roughness of 38.3?nm for the thick film made from 40?wt% solid slurry was found to be superior compared to other samples due to the presence of reduced crack and shrinkage. MLV fired at 950?°C for 1.5?h exhibited a coefficient of nonlinearity of 18 and breakdown voltage of 291.5?V that yields superior properties compared to commercial MLVs.     

Direct model-based predictive control scheme without cost function for voltage source inverters with reduced common-mode voltage

This paper presents a direct model-based predictive control scheme for voltage source inverters (VSIs) with reduced common-mode voltages (CMVs). The developed method directly finds optimal vectors without using repetitive calculation of a cost function. To adjust output currents with the CMVs in the range of –V_dc/6 to +V_dc/6, the developed method uses voltage vectors, as finite control resources, excluding zero voltage vectors which produce the CMVs in the VSI within ±V_dc/2. In a model-based predictive control (MPC), not using zero voltage vectors increases the output current ripples and the current errors. To alleviate these problems, the developed method uses two non-zero voltage vectors in one sampling step. In addition, the voltage vectors scheduled to be used are directly selected at every sampling step once the developed method calculates the future reference voltage vector, saving the efforts of repeatedly calculating the cost function. And the two non-zero voltage vectors are optimally allocated to make the output current approach the reference current as close as possible. Thus, low CMV, rapid current-following capability and sufficient output current ripple performance are attained by the developed method. The results of a simulation and an experiment verify the effectiveness of the developed method.