Multilevel inverter using cascaded 3-phase transformers with common-arm configuration

In multilevel inverter development for 3-phase applications, total number of transformer in the circuit can be reduced by using of cascaded 3-phase transformer circuit instead of single-phase transformer circuit. In the scheme, total number of switching components in the circuit is still a drawback to achieve lower cost and smaller size of the inverter compared with conventional multilevel inverter. This paper includes a challenging method to reduce total switching components in the multilevel inverter by adopting common-arm structure.The proposed inverter has been operated by two control schemes, Newton-Raphson and Equal-area method. After theoretical and experimental comparison of the methods, we found that Newton-Raphson method is useful to eliminate a specific harmonic order. However, the method has a shortcoming in real time operation which is performed by iterative calculation of the nonlinear equations. With Equal-area method, we can easily find the switching angles by calculating a trigonometric function. It can sufficiently minimize Total Harmonic Distortion (THD) of output voltage in real time operation of Digital Signal Processor (DSP).     

High-quality low-complexity wavelet-based compression algorithm for audio signals

Wavelets have recently emerged as a powerful tool for signal compression, particularly in the areas of image, video, and audio compression. In this paper, we present a low-complexity wavelet-based audio compression algorithm that is capable of handling fairly arbitrary audio sources. The algorithm transforms the incoming audio data into the wavelet domain, and compresses data by exploring redundancy in the wavelet coefficients and exploiting the large runs of zeros in the transformed signal. Also there is a possibility of applying a threshold to the non-zero coefficients, thus a further increase in the number of zeros is expected. The audio signal is first preprocessed to scale down the wavelet coefficients. Then the preprocessed signal is wavelet transformed using a bi-orthogonal discrete wavelet transform (DWT) and threshold by applying energy compaction strategy. Encoding represents the threshold coefficients in compact form. A new encoding technique that is easy to implement, and that provides a reasonable compression ratio for a certain acceptable distortion level has been developed to encode the threshold DWT. So, a bit rate can be controlled such that the algorithm operates at virtually any pre-selected bit rate. The motivation of using the bi-orthogonal wavelet transform is that it permits the use of a much broader class of filters, and this class includes symmetric linear phase filters. The superior performance of this algorithm is also demonstrated by comparing it with two other popular audio compression techniques and this meets the requirements of multimedia computing.     

多绕组高频变压器隔离式多电平变换器研究

为在高压大功率变换领域中省去工频变压器,并实现隔离、功率平衡和能量双向流动,提出了一种高频变压器隔离式级联型多电平变换器拓扑。级联H桥整流器和级联型逆变器的各个直流母线与采用多绕组高频变压器的隔离单元相连接,可通过多绕组变压器简单地实现各级负载不均衡时的功率平衡。本文给出了多绕组高频变压器隔离式多电平变换器的拓扑结构,并给出了包括级联H桥整流器控制和高频隔离单元控制的控制策略。实验结果验证了本文提出的拓扑和控制策略的正确性。     

Mathematical model of five-level ac/dc converter in abc reference frame

This paper proposes a mathematical model for three-phase multilevel diode clamped ac/dc converter (DCC) in abc-reference frame, in order to study dynamic responses and stability of the system, where multilevel converters are employed. An attempt is made to model the converter adopting 5-level DCC and can be easily extended to DCC with any number of levels. The converter output and dc capacitor voltages are expressed in terms of input source currents and switching functions; which are basic inputs provided to a converter. Connection and capacitor currents of the converter have been analyzed. The effectiveness of the proposed mathematical model is verified by the computer simulations and experimental results. The obtained mathematical model has been validated with the physical converter model in MATLAB/Simulink environment and the prototype model using dSPACE DS under closed loop control system. The developed mathematical model equations are able to represent the physical converter with similar characteristics.     

电压电流双闭环瞬时值控制级联逆变器研究

本文第一部分对单相级联型逆变器的几种PWM调制技术较详细的理论和仿真对比分析，找出它们的内在联系，并从中找出单相级联型逆变器的最佳调制方案。第二部分针对该种调制方案应用电压电流双闭环瞬时值反馈技术制作了一台原理样机，瞬时值控制技术的采用可以加快系统的动态响应和提高非线性负载适应能力。在电流控制环中，用电容电流反馈取代传统的电感电流反馈可以显著提高系统的外特性硬度。仿真和试验验证了电压电流双闭环瞬时值控制级联逆变器具有优良的稳态和动态性能。     

一种新型单相不对称五电平逆变器

该文对一种新型单相不对称五电平逆变器进行研究，这种新型逆变器是通过将半桥二极管钳位逆变器和传统两电平半桥逆变器共享同一直流母线而获得的。针对这种新型拓扑结构该文分析了一种方波合成与消谐波三角载波PWM相结合的控制方法，在这种控制方法下，新型逆变器允许开关速度较快的器件和耐压值较高的器件工作在一起。文中将这种逆变器与其它三种单相五电平逆变器进行了比较。最后本文对一个单相五电平不对称逆变器电路进行了实验验证，并给出相关结论。     

一种光斑图像的阈值分割和光斑中心坐标的计算方法

工业测量中经常需要从获取的光斑图像中提取光斑区域．计算光斑中心的坐标。针对光斑图像具有背景区域较暗且面积大,目标（光斑）区域较亮且面积小的特点,提出了一种适用于光斑图像的阈值分割方法．计算单个光斑中心坐标的重心法．以及采用连通区域标记和区域大小排序计算多个光斑中心坐标的方法。与其他闽值分割方法比较后的实验结果表明,所提出的方法可更好地分割光斑图像。与期望的人工选取的闽值最接近．计算得到的光斑中心坐标准确．且运行时间较短。     

Individual internet usage and the availability of online content of local interest: A multilevel approach

This paper illustrates whether the availability of online content of local interest affects the likelihood of individuals to connect to the internet and spend more time online. While the literature demonstrates a number of factors which push or enable individuals to spend more time online, we know little about the conditions that pull or attract individuals online. Although we know that individuals use the internet to access information, we do not know whether such attraction forces are relevant at the local scale too. Gaining a better understanding of how such mechanisms work at the local scale can assist our efforts to bridge digital divides, which tend to be geographically clustered. To explore this we utilise innovative data, which contain all the archived webpages under the UK top level domain name (.uk) and we calculate the volume of internet content of local interest at the neighbourhood level using the geolocation information included in the text of these webpages. Specifically, we calculate the radius of gyration for every archived website using the different postcodes included in the archived webpages and then we create an aggregated measure at the neighbourhood level discounting websites that have less of a local focus. We merge this measure of Local Internet Content (LIC) with a large population survey, which contains information about the frequency of internet usage in the UK and estimate the effect of LIC on the likelihood of an individual being a frequent internet user. Multilevel models are employed to utilise both individual and geographical level characteristics. Our results indicate that even after controlling for the individual and geographical characteristics, which according to previous studies affect internet usage, the availability of internet content of local interest still attracts individuals online.     

红外图像统计闭值分割方法

经典的统计阈值方法采用某种形式的类方差和作为阈值选择的准则,未考虑实际图像的特性,对目标和背景具有相似统计分布的图像的分割效果不甚理想。为此,利用阈值分割后两个类的标准偏差定义了一个新的阈值选择准则,并通过最小化此准则选择出最佳分割阈值。通过一系列实际图像上的实验结果表明,与现有的几种经典阈值分割方法相比,本方法分割图像的效果更好,尤其是对红外图像分割的效果更为明显。     

A structured marketplace for arbitrary services

Creating simple marketplaces with common rules, that enable the dynamic selection and consumption of functionality, is the missing link to allow small businesses to enter the cloud, not only as consumers, but also as vendors. In this paper, we present the concepts behind a hybrid service and process repository that can act as the foundation for such a marketplace, as well as a prototype that allowed us to test various real-world scenarios. The advantage of a hybrid service and process repository is that, it not only holds a flat list of services, but also exposes a generic set of use cases, that it obtains information on how specific services can be used to implement the use cases as well as information to select services at run-time according to customer’s goal functions.