Table-based PWM for all-digital RF transmitters

In this paper, a novel pulse-width modulator (PWM) for an all-digital PWM transmitter based on switching amplification is presented. In this approach, each symbol is represented by a sequence of pre-computed PWM pulse widths stored in a table that results in reduced error vector magnitude (EVM). A high-resolution pulse former is then used to build the bipolar radio frequency (RF) signal. Simulations and comparisons to other approaches reported in the literature under different oversampling ratios and finite time resolutions are presented. The impact of nonlinearities in the variable duty-cycle generator is also analyzed to demonstrate the robustness of the proposed technique.     

Spatial power combining for high-power transmitters

This article surveys recent progress in the development of high-power microwave and millimeter-wave solid-state sources using spatial power-combining techniques. Several promising topologies are discussed, and four technology demonstrations are presented that have emerged from recent research in academia and industry. We also include a brief discussion of potential applications and systems insertion issues     

Efficient wavelength selective soliton switching using fibergratings in single and cascaded nonlinear optical loop mirrors

The soliton switching performance of the nonlinear optical loop mirror (NOLM) with inserted fiber Bragg grating is examined numerically in this paper. The relationships between various grating designs to the self-switching characteristics of the device are presented, including cases where low switching powers and rapid switching transitions are observed. Particular attention is paid to the bandpass nonlinear switching behavior of the NOLM, introduced with the inclusion of the grating. This analysis is extended to consider a novel cascaded loop configuration, in which the gratings in each loop are tuned to a different wavelength. A three-channel simulation of a two-loop cascade is presented with a discussion on the suitability of the NOLM device to wavelength-division-multiplexing (WDM) applications     

晋城电力通信程控交换系统组网技术方案

数字程控交换系统作为电力通信网络的中枢节点在目前的通信网络中仍然发挥着不可替代的作用,文章针对晋城供电公司根据通信现状和用户需求,提出了采用C&C08B交换机与Hartis20-20LH交换机并列运行方式组建晋城程控交换系统网络,达到了地调和各县局用户进行各种业务互不影响的需求,基本实现了全网的统一出口、统一计费、统一管理,大大提高通信网的可靠性和先进性.     

Photonics for switching and routing

The ongoing growth of data traffic from existing and new applications poses a challenge to the packet-switched network infrastructure. High-capacity transport can be achieved in such networks by using dense wavelength-division-multiplexed systems, and reconfigurable optical add-drop multiplexers allow the optical layer to provision wavelength-based circuits between routing nodes. However, construction of the high-capacity packet routers provides significant scaling issues due to complexity, interconnect, and thermal limits. In this paper we will not seek to cover all aspects of optical packet switching and routing but outline some of the challenges facing the construction of such future routers and describe the role photonics can have in overcoming some of these issues. We will discuss how photonics' primary role will be to provide interconnection between racks of electronic routing elements and describe how fast wavelength switching can provide a high-capacity distributed switch fabric that will allow these packet routers to scale to higher capacities. The fast wavelength switching can be seen as the packet analog of wavelength-based circuit switching of today's transparent optical networks.     

主变备自投及过载切负荷装置的应用

分析了主变备自投及过载切负荷装置在应用过程中存在的问题,针对该装置的特点,结合实际,提出了相应的解决方案。     

Fiber parametric amplifiers for wavelength band conversion

By using a loop configuration formed by a polarization beam splitter, we experimentally demonstrate that the existing wavelength-division multiplexing (WDM) sources in C-band can be wavelength converted to the S-band with low polarization sensitivity and low crosstalk. Using a fiber parametric amplifier as a band converter, we achieve experimentally <0.65-dB polarization sensitivity and >4.7-dB conversion efficiency over 30-nm conversion bandwidth in 315 m of fiber. Compared to the conventional straight fiber wavelength conversion scheme, a more than 2-dB improvement in polarization sensitivity is measured. In addition to the polarization insensitivity, channel crosstalk is measured to be <-27 dB in 315 m of high nonlinearity fiber. In a detailed experimental study, the pattern of crosstalk in longer fiber lengths and the coupling between the polarization sensitivity and crosstalk are measured. For example, with a 430-m fiber length, we measure the degradation in polarization sensitivity to be ~4 dB for 12-dB increased signal power. The experimental results are also confirmed by theoretical calculations. Moreover, in a 32 channels systems simulation, the signal-to-noise ratio (SNR) of the converted signals after 800-km propagation is calculated to be only 0.8-dB degraded compared to using laser diodes with the same initial SNR values. Furthermore, we calculate the effect of pump noise and show that the relative intensity noise of the pump is transferred to the converted signals with an additional 8-dB/Hz degradation     

静止同步补偿器的开关函数建模与仿真

针对目前静止同步补偿器(Static Synchronous Compensator,STATCOM)输出建模和拓扑建模等方法的不足,通过引入单极性二值逻辑开关函数,建立了基于变换器物理特性和拓扑结构的开关函数模型.该模型的参数都是装置实际的物理参数,易于确定,更具一般性.对380V两机系统进行的仿真计算证明了所提模型和方法的正确性和有效性,并验证了STATCOM对系统无功补偿和电压稳定具有重要作用.     

Optimal routing and wavelength assignment for survivable multifibre WDM networks

Multifibre optical networks use a bundle of fibres to realize a link between two optical nodes. Such networks can offer significant economic benefits over single-fibre networks because of their ability to relax the restrictions imposed by the wavelength continuity constraint and their potential for handling future growth. This paper introduces two new and efficient integer linear program (ILP) formulations for dynamic wavelength allocation in survivable multifibre wavelength-division multiplexing (WDM) networks, using dedicated and shared protection. Single-fibre networks, both with and without wavelength conversion, can be treated as a special case of these formulations. The new formulations have been tested on several well-known WDM networks, and the results have been compared to those for single-fibre networks. A simple heuristic for dynamic lightpath allocation is also proposed, and its performance is validated by a comparison of the results to optimal solutions generated by the ILPs. Experimental results demonstrate that the new ILPs are feasible for current networks under low-to-medium traffic. For very large or highly congested networks, the heuristic can be used.     

Optimum nonblocking networks for photonic switching

We systematically minimize the number of elements in a N×N crossconnect consisting of 2×2 elements. The derivation covers all cases of interest, including dilated arrangements with negligible crosstalk. The relationship between number of elements and important parameters such as crosstalk, depth, and width is obtained. If N is not too large, and if stringent requirements are imposed on loss and crosstalk, then we show that the N×N arrangement is best realized using binary trees. The derivation also applies to arrangements including wavelength routers and channel adding/dropping filters     

开关变换器双频率控制技术

提出并研究一种开关变换器非线性控制策略,双频率控制技术.研究电压型和电流型双频率控制开关变换器的实现方式及特点,对比分析电压型和电流型双频率控制开关变换器的工作特性和控制规律.理论分析、仿真及实验结果表明:电压型和电流型双频率控制具有相同的稳态工作特性;而在动态响应方面,电流型双频率控制具有比电压型双频率控制更为优越的性能.此外,与电压型双频率控制相比,电流型双频率控制具有自动限流功能和更为平稳的启动特性.     

Minimum switching control for adaptive tracking

The switching adaptive control method has been used for quite a few years to solve the adaptive stabilization and model reference adaptive control problems. However, a serious problem with the switching control method is that the number of ‘candidate’ controllers can potentially be very large, especially for multi‐input–multi‐output systems. In this paper, we consider a class of minimum‐phase multi‐input–multi‐output plants with some mild compactness assumptions. Given any polynomial reference input, we provide a switching control law which guarantees exponentially stability of the closed‐loop system with exponential tracking performance. The main contribution of the paper is that we give the minimum number of candidate controllers required for switching. In particular, the number is equal to 2 for single‐input–single‐output plants (one for each sign of the high‐frequency gain), and is equal to 2^m for m‐input–m‐output plants. That is, the number is independent of the degree and the relative degree of the plant. Copyright © 2006 John Wiley & Sons, Ltd.     

Threshold conditions for an ultraviolet wavelength GaN quantum-welllaser

This paper describes an analysis of the threshold conditions for a GaN-AlGaN strained quantum-well (QW) laser. Gain spectra are computed using a many-body microscopic laser theory. The spontaneous emission rates are extracted from the gain spectra using a phenomenological expression based on energy conservation arguments. From the gain and spontaneous emission spectra, threshold current densities are estimated. Inhomogeneous broadening due to spatial variations in QW thickness are included in the analysis. Gain-current characteristics are determined for a number of laser heterostructure designs where the GaN QW width and Al composition of the AlGaN barrier material are varied     

A one-room-schoolhouse plan for engineering education

The one room schoolhouse plan for education, which stipulates that one lead professor works with a small group of students in most of their major courses during their junior, senior, and graduate years, is proposed. The program would rely on regular courses and faculty to supply the technical content of some major courses and all the minor courses. The intent is to have a dedicated and strongly interactive group that will overcome the distracting effects of today's information explosion, technology explosion, and expanded curricula. To this end, the relevant curriculum factors (course selection, course priorities, and course contents) will be more efficiently managed, taught, and coordinated. Within the limitations of time and energy, the students should cover more effectively and widely the disparate curriculums of both major and minor courses in the program     

Corrective switching algorithm for relieving overloads and voltage violations

It is widely known that corrective switching, including transmission line switching, bus-bar switching, and shunt element switching, may change the states of the power systems, and consequently, affect the distribution of power flows, transmission losses, short circuit currents, voltage profiles as well as transient stability of power systems. In this paper, a new algorithm is developed to find the best line and bus-bar switching action for relieving overloads and voltage violations caused by system contingencies based on a sparse inverse technique and fast decoupled power flow with limited iteration count. A general model of bus-bar switching action is also presented such that the new algorithm can simulate any kind of complicated bus-bar switching action. Furthermore, on the basis of a newly proposed voltage distribution factor by multiple iterations in power flow calculation, a novel algorithm for corrective voltage control by shunt switching is developed. These two algorithms are then integrated into a corrective switching algorithm. Simulation results on the WECC 179-bus system indicate that the new corrective switching algorithm proposed in this paper can effectively solve certain problems of line overloads and voltage violations. The computation time required is also satisfactory.     

双路供电固体静态切换开关控制策略

在介绍用于电压暂降抑制的双路供电固体静态切换开关(SSTS)工作原理的基础上,给出了兼备快速性和可靠性的电压暂降检测方法.利用dq变换瞬时检测主供电回路及备用供电回路的电压有效值,经低通滤波器滤除噪声干扰.所得结果与敏感负荷暂降极限电压值比较决定切换指令的发送.在讨论BBM和MBB切换控制策略的基础上.提出了综合考虑快速性和安全性的新型BBM切换方法,通过检测晶闸管压降判断主电源侧晶闸管导通状况,依据导通状况分别控制备用电源侧各相不同方向的晶闸管,通过施加反向电压,强迫原导通晶闸管的快速关断,达到既不形成环流又能快速切换的目的.基于电磁暂态的数字仿真验证了所提切换控制策略的正确性及有效性.开关时间可限定在5ms内,不会引起敏感性负荷的故障.     

Improved calculations for no-load transformer switching surges

This paper deals with a modeling of components and calculation of transient overvoltages that build up on the transformer primary terminals after the transformer has been switched off by a vacuum circuit breaker (VCB). The transformer is connected to the circuit breaker by a cable. The transient overvoltages are calculated for different cable lengths, and the cumulative probability of different arc angles is investigated. In this study two cases are considered: transient overvoltages due to steady-state magnetizing current switching, and transient overvoltages due to inrush current switching. It is shown that the case of inrush current switching is worse, as virtual current chopping is possible. The cable is modeled by pi sections, whereas the transformer model is based on a terminal impedance. The VCB re-ignitions are modeled by means of withstand voltage characteristics and high-frequency quenching capability. Due to shortage of field tests, this work uses only literature references to compare the results with actual measurements