单级功率因数校正变换器的拓扑研究

简单介绍了国内外的单级功率因数校正变换器电路。对其主要电路拓扑进行了适当分类。同时提出一种新型的单级AC/DC 变换器电路,并对电路的工作原理进行了分析和实验研究,得到了较为满意的实验结果。     

非理想条件下CCM模式Boost变换器的分析

本文以工作于电流连续模式下的Boost型变换器为例,根据能量守恒原理并用三端开关器件模型法建立了考虑电路元件的寄生效应以及开关元件的非理想开关特性时的大信号平均模型、DC和小信号电路模型.对寄生参数的存在给系统性能带来的影响进行了理论分析和仿真实验,分析与实验结果对进一步优化Boost型变换器性能具有很高的参考价值.     

直驱型风电系统大容量Boost PFC拓扑及控制方法

直驱型风力发电系统因其在风力机和发电机之间省去了增速装置,从而提高了系统的效率和可靠性,降低了系统维护费用和直接成本,并以其良好的低电压适应能力而受到越来越广泛的关注.然而,传统直驱系统采用三相不可控整流桥与带有大容量电容器的电压源电流控制型逆变器并网发电.这种结构向永磁同步发电机中注入了大量低频谐波,增加了系统损耗,进而减少了系统功率容量.针对其中的大容量Boost环节,提出一种将三个三相单管Boost型PFC电路并联,并采用载波相移技术加以控制的方案.仿真结果表明,在支路电流均工作于DCM模式的情况下,合成电流近似工作于CCM模式.实现了对永磁同步发电机的输出进行功率因数校正、降低发电机电流的谐波含量、改善永磁同步发电机的谐波特性、提高发电机有功功率输出能力和系统效率的目标.     

协同特征造型系统中细胞元模型动态分割和增量编辑*

针对基于瘦客户端结构的协同特征造型系统需要在服务器和客户端之间持续地传输庞大的数据模型,网络代价很高,提出一种基于细胞元模型的增量编辑方法。在服务器端对细胞元模型进行动态分割,识别并提取出一个很小变化的细胞元模型(CCM),然后传输到客户端并嵌入到编辑前的细胞元模型中。由于客户端向服务器发送的是造型指令和参数,而服务器反馈回客户端的是一个很小的变化的细胞元模型,从而降低了网络负荷,提高了更新效率。     

Generalizing intersection kernel support vector machines for color texture based recognition

This paper presents a novel recognition approach in which the component-adaptive color co-occurrence matrices (CACCMs) are designed to characterize color and texture cues in the images, while histogram intersection kernel support vector machines (HIKSVMs) are generalized to the version compatible to color co-occurrence matrix (CCM), called CCM intersection kernel support vector machines (CIKSVMs). An ensemble learning framework is proposed for synchronously training the optimal marginal CIKSVMs and corresponding CACCMs’ extractors. This learning architecture is applicable to an arbitrary color space employed for image coding, while we pay utmost attention to a perceptual uniform color space for the prominent potential in image proprieties’ display. For the formulation of recognition algorithm, the set of multi-channel CACCMs (CAMCMs) of per sample is utilized to get a balance between discriminative power and computational efficiency, while multiple marginal CIKSVMs are combined by weighted majority voting. The effectiveness of our approach is validated by promising results obtained from four experimental datasets.     

CCM 模式下的多输出DC􀀁DC 分析

多输出是DC-DC电路发展的一个重要趋势。在分析常规的多输出DC-DC结构及其工作原理基础上，系统研究了SIMO结构，该结构只使用一个电感，以各输出支路分时工作实现多输出。但由于电感共享，输出支路之间存在严重的交叉影响。若输出支路严格工作于DCM/PCCM模式下，可抑制这种交叉影响。在此基础上，提出了一个新的控制方式，在没有交叉影响CCM模式下实现SIMO工作。     

2 MeV proton channeling contrast microscopy of LEO GaN thin film structures

The recent development of blue and green light emitting diodes (LED) based on single quantum well structures made from GaN and related materials (AlGaN, InGaN) has created large efforts to optimise the growth methods used in their production. Rutherford Backscattering (RBS), in combination with channeling analysis, is a powerful tool for the quantitative characterization of the depth profile and the crystallinity of such structures. New growth modes, e.g. lateral overgrowth processes, are being rapidly developed. Channeling contrast microscopy (CCM), which employs a focused ion beam in order to obtain laterally resolved channeling yield data, is ideally suited to determine micro structural characteristics, (e.g. defect densities, tilts in lattice planes, strain) of such samples. Here we report results from proton channeling contrast measurements of laterally overgrown GaN thin films. Such measurements require a sub-micron ion beam focus size as well as an highly stable accelerator system, both of which are available at the Research Centre for Nuclear Microscopy at the National University of Singapore, where an ultrastable Singletron accelerator was recently installed.     

关于涟钢厂1#步进冷床升降油缸断裂原因的探讨

针对涟钢三炼钢#步进冷床数次发生升降油缸断裂、油管裂开、平衡阀冲坏的事故,从受力角度进行简单分析,采取加装安全阀等措施,取得了良好的效果.     

胶料连续混炼新技术

介绍了倍耐力公司最新推出的胶料连续混炼新技术CCM，它主要由两台双螺杆挤出机和为之服务的多大通精密输送、配料及投料装置组成。生产成本低，每小时可产胶料250kg，混炼胶质量好，设备占地面积小，其与传统炼胶法比较，除需造粒外，优势显而易见。     

QPR and duty ratio feed‐forward control for vienna rectifier of HVDC supply system

The grid current of a Vienna rectifier will change from the continuous conduction mode (CCM ) to the discontinuous conduction mode (DCM ) when the load current or the inductance decreases. This deteriorates the grid current. Therefore, a strategy based on the variable duty ratio feed‐forward and quasi‐proportional‐resonant (QPR ) combined control is put forward, by introducing the needed duty ratio to the original output of current inner loop, whereby the pressure of the inner loop is effectively reduced. The working mechanism of the Vienna rectifier is first analyzed. The transfer functions of CCM and DCM between duty ratio and grid current are then built. At the same time, the parallel multi‐QPR harmonic compensators are adopted in the current inner loop to effectively eliminate the specific harmonic pollution. To verify the correctness and effectiveness of the proposed strategy, a 5.3‐kW prototype under digital control is established. The simulation and experimental results show that both the steady and transient performance of the proposed strategy are better under the fixed current inner loop parameters, the current zero crossing distortion can be eliminated, and the current quality acquired under the transformation between CCM to DCM can be further improved.