带谐波抑制策略的三电平脉冲整流器仿真研究

以城轨牵引供电系统中网侧变流器为研究对象,根据单相三电平脉冲整流器等效数学模型,应用瞬态电流控制策略,加入中点电位平衡策略,给出控制策略数学模型和控制方程.并根据脉冲整流器低次谐波消除原理,对该控制策略下,加入整理器低次谐波消除策略前后,脉冲整流器网侧和直流侧输入输出状态进行仿真研究.     

500kV断路器因空气压力低告警导致断路器控制保护回路断线分析

针对天生桥换流站500kV三菱断路器因空气压力低告警导致断路器控制保护回路断线这一情况,根据工作站中出现的信号,结合断路器的控制、保护二次回路,对信号及其出现的缘由进行分析,评估断路器控制保护回路断线时,可能出现的安全生产风险,发现目前存在的问题,并对这些问题提出解决方案。     

Effects of silicone oil and polymeric modifiers on the mechanical properties of highly filled LLDPE

The effects of coupling agents, silicone oil, and three types of polymeric modifiers on the mechanical properties of linear low density polyethylene (LLDPE) composites highly filled with aluminium hydroxide [Al(OH)₃] were studied. Polymeric modifiers that contain polar groups, such as silane‐grafted polyethylene (Si‐g‐PE) and acrylic‐acid‐grafted ethylene‐vinyl acetate copolymer (AA‐g‐EVA), improve the mechanical properties dramatically, while nonpolar modifiers improve them to some extent. When Al(OH)₃ was treated using a titanate coupling agent, the silicone oil increased the impact strength and elongation at break of the LLDPE/Al(OH)₃ composites. Introduction of a polymeric modifier containing polar groups destroys the beneficial effects of silicone oil on film mechanical properties, while the introduction of a nonpolar elastomeric polymeric modifier retains the high impact strength and elongation at break. SEM analyses provide the indirect evidence of the encapsulation of silicone oil around the filler. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 121–128, 2002     

Thermal expansion of an SiC particle-reinforced aluminum composite

Using a push-rod dilatometer, we measured between 76 and 390 K the thermal expansion of a particle-reinforced-composite wrought plate obtained by powdermetallurgy methods. The particles, 30% by volume, consisted of monocrystals of -SiC with sizes near 10 m. The matrix consisted of a 6061 aluminum alloy with original particle sizes near 20 m. We found the perpendicular thermal expansivity, ₃, higher by 26% than the in-plane thermal expansivity, ₁-₂. These values differ from a rule-of-mixture prediction by –3 and –23%, respectively. All three _i, components lie outside the Rosen-Hashin bounds. Levin's isotropic model agrees within 10% with the ₁-₂-₃ average. Both the anisotropy and the bounds violation result from microstructural nonhomogeneity arising from processing. Rosen and Hashin's transverse-isotropicsymmetry relationships account approximately for these effects by introducing the anisotropic elastic constants. Using neutron diffraction, we determined that the SiC particles are textureless.Paper presented at the Tenth International Thermal Expansion Symposium, June 6–7, 1989, Boulder, Colorado, U.S.A.     

Design of a broadband dielectric resonator antenna and its application in low sensitivity frequency beam‐scanning array with wide scanning angle and suppressed sidelobes

In this paper, a broadband dielectric resonator antenna (DRA) with a simple H‐slot feeding structure is proposed. The broad bandwidth (~45%) and uni‐directional radiation enable this DRA suitable to work as a radiation element in the construction of a beam‐scanning array with not only low frequency sensitivity which is important for accurate angle estimation of in‐coming targets, but also a wide scanning range. Moreover, stable coupling coefficients are established around all the above three resonances with respect to its corresponding feeding line, ensuring a low sidelobe level (SLL) across the whole operating frequency range. In order to realize such a DRA, a latticed rectangular structure is utilized to generate the lower two resonances, while the upper resonance is generated by its H‐shaped feeding slot. The shape of the latticed dielectric resonator is also modified according to a 3‐D printed fixing structure for an accurate installation. A 20‐element beam‐scanning prototype is demonstrated and manufactured. The range of scanning angle is from ?36° to +13° within the bandwidth of 10 to 16 GHz, corresponding to a frequency sensitivity of only 122.5 MHz/^o. The achieved SLL are smaller than 19 dB for all scanning beams. The above performance indicates that, this array is very suitable for near‐range radar systems requiring an accurate angle estimation.     

数学形态学在数字图像处理中的应用研究

传统边缘检测算法由于对噪声敏感,难以准确提取图像边缘,导致图像处理效果不佳.基于传统数学形态学算法中结构算子的方向性和尺寸几何的基础上进行算法改进.针对抗噪型碰撞腐蚀形态学边缘检测算子结构元素特征,采用不同大小结构元素组合来提取边缘特征,有效保证了图像细节的同时去掉较大噪声点.根据结构元素的方向性,利用同向结构元素图像的匹配来检测各边缘信息,确保不同向边缘信息的完整度.通过比较文本改进算法与传统的边缘检测算法对图像边缘检测效果表明:本文提出的改进算子在处理较大图像边缘检测时具有更快的检测速度,且图像边缘光滑,细节清晰,具备了更强的抗噪性能.     

基于稳健设计的SGNS算法的超参数调优方法

通常给定超参数的若干取值选取性能最大的为最优组合(称为直接选优法),但是此方法的稳健性差。为此,提出了一种基于稳健设计的超参数调优方法(称为稳健调优法)。具体地,以SGNS算法中的超参数调优为例,在词语推断任务上实验并得出:经方差分析得到SGNS算法中的七个超参数中的五个对算法预测性能有显著影响,确定为主控因子,其余两个确定为噪声因子,且主控因子中有三个对性能估计的方差有显著影响,因此,调优中仅从期望最大来直接选优是不合理的;稳健调优法与直接选优法两者在预测性能上没有显著差异,但稳健调优法对噪声因子具有较好的稳健性。稳健调优法对一般的深度神经网络的调参有实际的借鉴意义。     

IETCAM:基于信息熵的低功耗TCAM分类器

目前,三态内容寻址器被广泛应用于数据平面的高速转发,但现有的索引式TCAM在降低功耗和运行时间等方面仍存在问题.针对这些不足,提出了一种基于信息熵的低功耗索引式TCAM分类器,利用了信息熵技术,有效地解决了规则集在TCAM子块中分布不均、功耗较大的问题.实验表明,在2k大小的规则集下,该算法相较于经典的SmartPC算法平均可以提高63％的功耗降低率,运算时间更新速度缩小了97％,存储开销仅增加了10％.     

基于局部概率抽样的标签噪声过滤方法

分类学习任务中,在获取数据的过程中会不可避免地产生噪声,特别是标签噪声的存在不仅使得学习模型更复杂,而且容易造成过拟合并导致分类器泛化能力的下降。标签噪声过滤算法虽然在一定程度上可以解决上述问题,但是仍然存在噪声识别能力较差、分类效果不够理想以及过滤效率低等问题。针对这些问题,提出一种基于标签置信度分布的局部概率抽样方法来进行标签噪声过滤。首先利用随机森林分类器对样本的标签进行投票,从而获取每个样本的标签置信度;然后根据标签置信度的大小,将样本划分为易识别样本和难识别样本;最后分别采用不同的过滤策略对样本进行过滤。实验结果表明,在标签噪声存在的情况下,所提方法在大多数案例上能够保持较高的噪声识别能力,并且在分类泛化性能上也具有明显优势。     

Design of the low power wake-up receiver for internet of things communication

A wake-up receiver with high energy efficiency and low power consumption is proposed for solving the power consuming problems of wireless nodes communication in the Internet of Things. The proposed wake-up receiver based on the wake-up mechanism can effectively schedule the network nodes communication, and use the simple envelope detection structure to achieve frequency down-conversion, which can flexibly manage energy and reduce power consumption. Based on UMC 65nm CMOS process technology, the wake-up receiver is designed and simulated. The results show that it can achieve S₁₁ of -21dBm and a sensitivity of -75dBm at a data rate of 1Mb/s, when operating at the central frequency of 780MHz and input signal adopting an on-off keying (OOK) modulation, and the power consumption is 82μW at 1.2V voltage supply.