改进的正弦脉宽调制控制算法综述

正弦脉宽调制(SPWM)是逆变电路常采用的调制方法。合理的采用SPWM控制算法,能够减少逆变电路的低次谐波含量,降低总谐波系数(THD),提高直流电压的利用率,对改善逆变电路的输出性能具有重要意义。在介绍正弦脉宽调制(SPWM)基本原理的基础上,根据目前SPWM波形主要由各种微处理器在软件支持下产生的特点,对一些改进的算法进行研究,详细分析了面积中心等效法、切线法、峰值型采样方式几种典型的改进控制算法,并讨论了各自的优缺点探讨了这些方法在不同领域的应用。     

A novel simulation technique for the analysis of digitalasynchronous pulse width modulation

A digital simulation technique based on single Fourier series is used to predict the spectra, including the nonintegral harmonics, generated by digital asynchronous pulse width modulation invertors. The results, with an accuracy of 70 dB, are superior to the results obtained with fast Fourier transform techniques, and offer an alternative to the complex methods based on double Fourier integration and Bessel functions. The technique is applicable to any choice of reference waveform. Output distortion with the introduction of minimum pulse and dead time is studied     

Spectrum of a frequency modulated pulse width modulation signal

In power electronics, the switching elements are controlled by pulse width modulated (PWM) signals making their currents on and off repeatedly. This might cause electromagnetic interference (EMI) problems especially in switched mode power supplies. One method for mitigating the EMI is to use the frequency modulation technique in the control signal of the switching metal–oxide–semiconductor field‐effect transistor. According to this approach, frequency of the PWM signal is modulated in order to spread its spectrum and hence reduce the EMI levels. This paper presents the theoretical analysis for the spectrum of a frequency modulated PWM signal. Copyright © 2013 John Wiley & Sons, Ltd.     

Programmed PWM techniques to eliminate harmonics: a criticalevaluation

Programmed pulsewidth modulators (PWMs) eliminating several lower-order harmonics generate high-quality output spectra, which in turn result in minimum current ripple and reduced torque pulsations, thereby satisfying several performance criteria and contributing to overall improved performance. Several programmed PWM switching patterns to eliminate harmonics in the output spectra of single-phase and three-phase inverters are possible. Each of these leads to a specific advantage in single- and three-phase inverters, depending on the application. First, the superiority of programmed PWM techniques over the conventional carrier-modulated PWMs is established. Next, a critical evaluation of the programmed PWM schemes on the basis of applications for single- and three-phase inverters is used to provide a framework and guidelines for the selection of the appropriate technique for each application area. Evaluation criteria include harmonic loss factor and total harmonic distortion factors defined at the input and output of the inverter terminals. Finally, a simple low-cost solution for obtaining the required PWM switching points is proposed. Selected results are verified experimentally     

Buck变换器跨周期调制(PSM)同步开关映射模型

跨周期高制(PSM)模式作为优良的调制模式，在小功率智能集成苡片设计中得到逐步应用，与PWM调制模式相比，PSM调制模式具有静态功耗小，轻负载系统转换效率高等优点。状态空间平无法能够分析PSM变换器的动态特性，但只适用于分析低频特性，对于工作在较高频率的功率集成芯片，需要建立PSM工作模式下的大信号模型。本文根据建军立的同步开关映射模型，对离散导通模式的Buck变换器的非线性特性进行分析，从输出电压负载电阻变化关系图中直接得到PSM调制模式跨周期数目的变化规律，通过电路信真验证模型的正确。     

A novel variable frequency modulation technique to improve light‐load efficiency for multiphase synchronous rectified VRM

A novel variable frequency modulation technique for multiphase synchronous rectified voltage regulator module (VRM) is proposed in this paper. The proposed technique provides zero voltage switching (ZVS) for high‐side and low‐side power switches under both light‐ and heavy‐load conditions, thereby increasing the efficiency as compared to the conventional approach. The dependency of switching frequency on the load condition for the proposed modulation technique and the related conduction loss are analyzed. It will be shown that the frequency increases for light‐load condition in order to retain ZVS and decrease the conduction loss. Although the switching loss will slightly increase due to the increase of switching frequency, the analysis and experimental results will show that the contribution of frequency increasing can cover this additional loss. Experimental results derived from a single‐phase and an eight‐phase synchronous rectified VRM show that the proposed modulation technique is superior to the conventional one and compared to conventional constant switching frequency techniques with 250 and 550thinspacekHz, the efficiency can be increased up to 17 and 5% for single‐phase VRM and 8 and 4% for eight‐phase VRM under various load conditions. Even an off‐the‐shelf controller with an additional simple and cheap control circuit comprising one switch, two operational amplifiers and several resistors is used to realize the proposed technique, that is, a very low cost and small circuitry is attached to gain the significant benefit. Copyright © 2011 John Wiley & Sons, Ltd.     

新型平板热管的传热性能研究

为了提高普通蒸汽腔平板热管的机械强度和传热性能，提出了一种热端与冷端之间设有液态工质回流柱的新型平板热管，并对以该种平板热管为热扩散基板的集成模块的传热性能进行了实验研究。研究结果表明，在热耗散功率较大时，平板热管基板模块的结壳热阻、管芯至基板间热阻均比纯铜基板模块小，而且其结壳热阻分别比同厚度和同重量的纯铜基板模块的结壳热阻小30％和40％。该结果说明新型平板热管比纯铜基板具有更好的热扩散性能，适合于大功率模块设计     

新型单相应急电源(EPS)的研制

针对目前EPS(Emergency Power Supply,EPS)应急电源切换速度慢的问题,提出了一种快速切换的单相应急电源的数字化解决方案.基于锁相原理,令EPS输出电压和市电电压的大小、频率、相位保持一致,用DSP实现了EPS的快速切换技术,同时提出了一种简单的蓄电池在线监测系统硬件实现方式.并设计了一台50 Hz,220 V/1.5 kVA的EPS应急电源,采用继电器切换,从市电出现异常时刻开始到切换完成时刻止,切换时间小于10 ms.     

过程控制软件标准接口剖析(3)——COM组件开发方法

COM应用主要是 Server/Client (客户 /服务器 )模式 ,开发 COM组件既可以使用 MFC,也可以使用 ATL,由于使用基于模板库的 ATL 框架开发 COM组件应用具有独特的优势 ,因此本文以一个简单例子详细介绍了如何利用 ATL创建 COM组件与 COM客户 ,进一步阐明了 COM服务器组件的二进制兼容性。     

The application of novel polypropylene to the insulation of electric power cable (3)

Having a higher melting temperature than polyethylene, polypropylene has been expected to be an insulation material for power cables. But isotactic polypropylene (i‐PP) used generally is unsuitable as cable insulation because it shows poor flexibility, low breakdown strength due to growing spherulites, and so on. But stereoregular syndiotactic polypropylene (s‐PP) newly developed with metallocene catalyst shows quite different properties than i‐PP. In our previous paper, we investigated the basic properties of s‐PP and the initial properties as a cable which was manufactured using s‐PP insulation. It was revealed that s‐PP had superior thermal and electrical properties to cross‐linked polyethylene and the s‐PP insulation table showed satisfactory initial properties. However, in order to apply to an actual cable, the properties must be maintainable over 30 years after construction. In this paper, we estimated the long‐term remaining properties for s‐PP insulation table. A series of experiments on long‐term properties gave the following results: (1) s‐PP cable shows longer life over 30 years; (2) the breakdown strength of s‐PP cable after a long‐term experiment equal to 30 years is slightly lower than the initial breakdown strength, but it is sufficient as a remaining property. Furthermore, water‐tree resistivity of s‐PP was investigated and it was revealed that s‐PP significantly suppressed the water tree propagation compared with XLPE. These results suggested that s‐PP cable would serve as a next‐generation cable. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 1–8, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20114     

Laser intensity modulation method (LIMM): review of the fundamentals and a new method for data analysis

The laser intensity modulation method (LIMM) is widely used for the determination of the spatial distribution of polarization in ceramics, single crystals and polymers. A brief history of the origin and development of LIMM during the past 20 years is presented. The experimental technique and the derivation of the LIMM equation are described. The data analysis requires the numerical solution of a Fredholm integral equation of the 1st kind. This is an illposed problem that has multiple and very different solutions. In this paper, a new technique is proposed that gives the polarization distribution in the form of a special 8th-degree polynomial. Both simulated and experimental data are analyzed with the new technique.     

Crosstalk noise analysis of coupled on-chip interconnects using a multiresolution time domain (MRTD) technique

Journal of Computational Electronics - In this paper, crosstalk noise analysis of coupled on-chip interconnects is presented. The multiresolution time domain (MRTD) method is used to analyze the...     

Optimal location and sizing of Unified Power Flow Controller (UPFC) to improve dynamic stability: A hybrid technique

In this paper a hybrid technique based optimal location and sizing of UPFC to improve the dynamic stability is proposed. Here, the maximum power loss bus is identified at the most favorable location for fixing the UPFC, because the generator outage affects the power flow constraints such as power loss, voltage, real and reactive power flow. The optimum location has been determined using the Artificial Bees Colony (ABC) algorithm. Depending on the violated power flow quantities the Gravitational Search Algorithm (GSA) optimizes the required quantity of the UPFC to recover the initial operating condition. Then the proposed work is implemented in the MATLAB/simulink platform and the performance is evaluated by using the comparison, at different techniques like ABC and GSA. The comparison results demonstrate the superiority of the proposed approach and confirm its potential to solve the problem.     

Enhancement of ferroelectricity in gadolinium (Gd) and transition metal (Ni, Co, Cr) Co-doped BiFeO3 thin films via a chemical solution deposition technique

The BiFeO₃ (BFO) and the gadolinium and transition metal ions co-doped (Bi_0.9Gd_0.1)(Fe_0.975 TM _0.025)O_3-δ (TM?=?Ni, Co and Cr, BGFNi, BGFCo and BGFCr) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Compared to the pure BFO, improved electrical and ferroelectric properties were observed in the co-doped (Bi_0.9Gd_0.1)(Fe_0.975 TM _0.025)O_3-δ thin films. Among the thin films, the BGFCr thin film exhibited large remnant polarization (2P _r ), low coercive field (2E _c ), and reduced leakage current density, which are 136 μC/cm², 1360 kV/cm at 1470 kV/cm, and 5.14?×?10^-6 A/cm² at 100 kV/cm, respectively.     

改性含氮杂环聚醚砜酮绝缘漆的合成、表征及应用研究

以合成的含二氮杂萘酮结构的聚醚砜酮(PPESK)为基础,然后对其进行羟基化改性,用FT-IR和^1H-NMR表征分子链结构,并和小分子量的聚氨脂发生交联反应制成了性能良好的绝缘漆。     

Electrical Stimulation of the Proprioceptive Cortex (Area 3a) Used to Instruct a Behaving Monkey

A growing number of brain-machine interfaces have now been developed that allow movements of an external device to be controlled using recordings from the brain. This work has been undertaken with a number of different animal models, as well as several human patients with quadriplegia. The resulting movements, whether of computer cursors or robotic limbs, remain quite slow and unstable compared to normal limb movements. It is an open question, how much of this instability is the result of the limited forward control path, and how much has to do with the total lack of normal proprioceptive feedback. We have begun preliminary studies of the effectiveness of electrical stimulation in the proprioceptive area of the primary somatosensory cortex (area 3a) as a potential means to deliver an artificial sense of proprioception to a monkey. We have demonstrated that it is possible for the monkey to detect brief stimulus trains at relatively low current levels, and to discriminate between trains of different frequencies. These observations need to be expanded to include more complex, time-varying waveforms that could potentially convey information about the state of the limb.     

Enhancing the design and performance of a gate-all-around (GAA) charge plasma nanowire field-effect transistor with the help of the negative-capacitance technique

A gate-all-around charge plasma nanowire field-effect transistor (GAA CP NW FET) device using the negative-capacitance technique is introduced, termed the GAA CP NW negative-capacitance (NC) FET. In the face of bottleneck issues in nanoscale devices such as rising power dissipation, new techniques must be introduced into FET structures to overcome their major limitations. Negative capacitance is an efficient effect that can be incorporated into a device to enhance its performance for low-power applications and help to reduce the operating voltage. The Landau–Khalatnikov equation can be applied in such cases to obtain the effective bias. To determine the effects of negative capacitance, lead zirconate titanate (PZT) ferroelectric material, a ceramic material with perovskite properties, is adopted as a gate insulator. This approach diminishes the supply voltage and reduces the power dissipation in the device. Excluding their polarization properties, ferroelectric materials are similar to dielectric materials, and PZT offers abundant polarization with improved reliability and a higher dielectric capacitance. Without proper tuning of the thickness of the PZT material, hysteresis behavior mat occur. Hence, the thickness of the PZT material (t_FE) is an essential parameter to optimize the device performance and achieve a reduced threshold voltage for the GAA CP NW NC-FET device proposed herein. Furthermore, varying the thickness of the PZT ferroelectric material can also enhance the performance. When using the highest values of t_FE, improved outcomes with an analogously lower operating voltage are observed. The effects of varying t_FE on the performance characteristics of the device including the drain current, transconductance, polarized charge, etc. are also interpreted herein.

     

关于(a,b,s)-临界图的邻域条件(英文)

设G是一个n阶的图.设a,b和s是整数,使得b>a≥1.设δ(G)是G的最小度.证明了:如果δ(G)≥(k-1)a+s,n≥(a+b)(k(a+b)-2)/b,并且|NG(x1)∪NG(x2)∪…∪NG(xk)|≥an/(a+b)+s对V(G)任意的独立子集{x1,x2,…,xk}都成立,这里k≥2,则G是一个(a,b,s) 临界图.这个结果在某种意义上是最好的.     

Solid state NMR, MRI and Sir Peter Mansfield: (1) from broad lines to narrow and back again; and (2) a highly tenuous link to landmine detection

The contributions of Sir Peter Mansfield to MRI are rooted in solid state NMR. I summarize some of the important contributions of Sir Peter to that field, provide a glimpse of the state of the art in multiple-pulse line-narrowing in the early 1970s, and indicate how the earliest MRI efforts at Nottingham flowed from solid state NMR. These line-narrowing methods, providing control over the Hamiltonian governing the dynamics of nuclear spins, continue to evolve and to find new uses. I indicate how some methods and ideas from solid state NMR of the 1970s are at present applied to the detection of explosives in landmines by nuclear quadrupole resonance (NQR). In honor of Sir Peter Mansfield     

我国的检验检测市场距离中介检验检测市场还有多远(续完)

2．4检验检测任务来源单一，检验检测市场需求不足，本末倒置，检验检测市场呈现“供大干求”状况 政府投资建立的检验检测机构，在检验检测市场竞争中，除了靠政府部门授权的名称，还依赖政府下达的强制性监督检验检测任务，CCC认证检验检测和生产许可证检验检测虽然没有指定唯一的检验检测机构承担检验检测任务，但供企业选择的余地也不多。在技术监督、农业、卫生几个主要领域，其检验检测机构的业务收入中委托检测业务呈上升趋势，但其中60％来自或者间接来自政府政策的影响。